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+---
+title: "Artificial gravity"
+chunk: 1/4
+source: "https://en.wikipedia.org/wiki/Artificial_gravity"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:12.372756+00:00"
+instance: "kb-cron"
+---
+
+Artificial gravity is the creation of an inertial force that mimics the effects of a gravitational force, usually by rotation. 
+Artificial gravity, or rotational gravity, is thus the appearance of a centrifugal force in a rotating frame of reference (the transmission of centripetal acceleration via normal force in the non-rotating frame of reference), as opposed to the force experienced in linear acceleration, which by the equivalence principle is indistinguishable from gravity.
+In a more general sense, "artificial gravity" may also refer to the effect of linear acceleration, e.g. by means of a rocket engine.
+Rotational simulated gravity has been used in simulations to help astronauts train for extreme conditions. 
+Rotational simulated gravity has been proposed as a solution in human spaceflight to the adverse health effects caused by prolonged weightlessness. 
+However, there are no current practical outer space applications of artificial gravity for humans due to concerns about the size and cost of a spacecraft necessary to produce a useful centripetal force comparable to the gravitational field strength on Earth (g).
+Scientists are concerned about the effect of such a system on the inner ear of the occupants. The concern is that using centripetal force to create artificial gravity will cause disturbances in the inner ear leading to nausea and disorientation. The adverse effects may prove intolerable for the occupants.
+
+== Centrifugal force ==
+
+In the context of a rotating space station, it is the radial force provided by the spacecraft's hull that acts as centripetal force. Thus, the "gravity" force felt by an object is the centrifugal force perceived in the rotating frame of reference as pointing "downwards" towards the hull.
+By Newton's third law, the value of little g (the perceived "downward" acceleration) is equal in magnitude and opposite in direction to the centripetal acceleration. It was tested with satellites like Bion 3 (1975) and Bion 4 (1977); they both had centrifuges on board to put some specimens in an artificial gravity environment.
+
+=== Differences from normal gravity ===
+
+From the perspective of people rotating with the habitat, artificial gravity by rotation behaves similarly to normal gravity but with the following differences, which can be mitigated by increasing the radius of a space station.
+
+Centrifugal force varies with distance: Unlike real gravity, the apparent force felt by observers in the habitat pushes radially outward from the axis, and the centrifugal force is directly proportional to the distance from the axis of the habitat. With a small radius of rotation, a standing person's head would feel significantly less gravity than their feet. Likewise, passengers who move in a space station experience changes in apparent weight in different parts of the body.
+The Coriolis effect gives an apparent force that acts on objects that are moving relative to a rotating reference frame. This apparent force acts at right angles to the motion and the rotation axis and tends to curve the motion in the opposite sense to the habitat's spin. If an astronaut inside a rotating artificial gravity environment moves towards or away from the axis of rotation, they will feel a force pushing them in or against the direction of spin. These forces act on the semicircular canals of the inner ear and can cause dizziness. Lengthening the period of rotation (lower spin rate) reduces the Coriolis force and its effects. It is generally believed that at 2 rpm or less, no adverse effects from the Coriolis forces will occur, although humans have been shown to adapt to rates as high as 23 rpm.
+Changes in the rotation axis or rate of a spin would cause a disturbance in the artificial gravity field and stimulate the semicircular canals (refer to above). Any movement of mass within the station, including a movement of people, would shift the axis and could potentially cause a dangerous wobble. Thus, the rotation of a space station would need to be adequately stabilized, and any operations to deliberately change the rotation would need to be done slowly enough to be imperceptible. One possible solution to prevent the station from wobbling would be to use its liquid water supply as ballast which could be pumped between different sections of the station as required.
+
+=== Human spaceflight ===
+The Gemini 11 mission attempted in 1966 to produce artificial gravity by rotating the capsule around the Agena Target Vehicle to which it was attached by a 36-meter tether. They were able to generate a small amount of artificial gravity, about 0.00015 g, by firing their side thrusters to slowly rotate the combined craft like a slow-motion pair of bolas. The resultant force was too small to be felt by either astronaut, but objects were observed moving towards the "floor" of the capsule.
+
+==== Health benefits ====

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+title: "Artificial gravity"
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+source: "https://en.wikipedia.org/wiki/Artificial_gravity"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:12.372756+00:00"
+instance: "kb-cron"
+---
+
+Artificial gravity has been suggested as a solution to various health risks associated with spaceflight. In 1964, the Soviet space program believed that a human could not survive more than 14 days in space for fear that the heart and blood vessels would be unable to adapt to the weightless conditions. This fear was eventually discovered to be unfounded as spaceflights have now lasted up to 437 consecutive days, with missions aboard the International Space Station commonly lasting 6 months. However, the question of human safety in space did launch an investigation into the physical effects of prolonged exposure to weightlessness. In June 1991, the Spacelab Life Sciences 1 on the Space Shuttle flight STS-40 flight performed 18 experiments on two men and two women over nine days. In an environment without gravity, it was concluded that the response of white blood cells and muscle mass decreased. Additionally, within the first 24 hours spent in a weightless environment, blood volume decreased by 10%. Long periods of weightlessness can cause brain swelling and eyesight problems. Upon return to Earth, the effects of prolonged weightlessness continue to affect the human body as fluids pool back to the lower body, the heart rate rises, a drop in blood pressure occurs, and there is a reduced tolerance for exercise.
+Artificial gravity, for its ability to mimic the behavior of gravity on the human body, has been suggested as one of the most encompassing manners of combating the physical effects inherent in weightless environments. Other measures that have been suggested as symptomatic treatments include exercise, diet, and Pingvin suits. However, criticism of those methods lies in the fact that they do not fully eliminate health problems and require a variety of solutions to address all issues. Artificial gravity, in contrast, would remove the weightlessness inherent in space travel. By implementing artificial gravity, space travelers would never have to experience weightlessness or the associated side effects. Especially in a modern-day six-month journey to Mars, exposure to artificial gravity is suggested in either a continuous or intermittent form to prevent extreme debilitation to the astronauts during travel.
+
+==== Proposals ====
+
+Several proposals have incorporated artificial gravity into their design:
+
+Kosmos 936: A collaborative medical research satellite launched in 1977 by the Soviet Union that included experiments studying the effects of centrifugal artificial gravity on rats. The rats in the centrifuges did have higher bone density upon return than those that were not in centrifuges, but not as high as those that remained on earth.
+Discovery II: a 2005 vehicle proposal capable of delivering a 172-metric-ton crew to Jupiter's orbit in 118 days. A very small portion of the 1,690-metric-ton craft would incorporate a centrifugal crew station.
+Multi-Mission Space Exploration Vehicle (MMSEV): a 2011 NASA proposal for a long-duration crewed space transport vehicle; it included a rotational artificial gravity space habitat intended to promote crew health for a crew of up to six persons on missions of up to two years in duration. The torus-ring centrifuge would utilize both standard metal-frame and inflatable spacecraft structures and would provide 0.11 to 0.69 g if built with the 40 feet (12 m) diameter option.
+ISS Centrifuge Demo: a 2011 NASA proposal for a demonstration project preparatory to the final design of the larger torus centrifuge space habitat for the Multi-Mission Space Exploration Vehicle. The structure would have an outside diameter of 30 feet (9.1 m) with a ring interior cross-section diameter of 30 inches (760 mm). It would provide 0.08 to 0.51 g partial gravity. This test and evaluation centrifuge would have the capability to become a Sleep Module for the ISS crew.
+Mars Direct: A plan for a crewed Mars mission created by NASA engineers Robert Zubrin and David Baker in 1990, later expanded upon in Zubrin's 1996 book The Case for Mars. The "Mars Habitat Unit", which would carry astronauts to Mars to join the previously launched "Earth Return Vehicle", would have had artificial gravity generated during flight by tying the spent upper stage of the booster to the Habitat Unit, and setting them both rotating about a common axis.
+The proposed Tempo3 mission rotates two halves of a spacecraft connected by a tether to test the feasibility of simulating gravity on a crewed mission to Mars.
+
+The Mars Gravity Biosatellite was a proposed mission meant to study the effect of artificial gravity on mammals. An artificial gravity field of 0.38 g (equivalent to Mars's surface gravity) was to be produced by rotation (32 rpm, radius of ca. 30 cm). Fifteen mice would have orbited Earth in LEO(Low Earth orbit) for five weeks and then land alive. However, the program was canceled on 24 June 2009, due to a lack of funding and shifting priorities at NASA.
+Vast Space is a private company that proposes to build the world's first artificial gravity space station using the rotating spacecraft concept.

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+title: "Artificial gravity"
+chunk: 3/4
+source: "https://en.wikipedia.org/wiki/Artificial_gravity"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:12.372756+00:00"
+instance: "kb-cron"
+---
+
+==== Issues with implementation ====
+Some of the reasons that artificial gravity remains unused today in spaceflight trace back to the problems inherent in implementation. One of the realistic methods of creating artificial gravity is the centrifugal effect caused by the centripetal force of the floor of a rotating structure pushing up on the person. In that model, however, issues arise in the size of the spacecraft. As expressed by John Page and Matthew Francis, the smaller a spacecraft (the shorter the radius of rotation), the more rapid the rotation that is required. As such, to simulate gravity, it would be better to utilize a larger spacecraft that rotates slowly. 
+The requirements on size about rotation are due to the differing forces on parts of the body at different distances from the axis of rotation. If parts of the body closer to the rotational axis experience a force that is significantly different from parts farther from the axis, then this could have adverse effects. Additionally, questions remain as to what the best way is to initially set the rotating motion in place without disturbing the stability of the whole spacecraft's orbit. At the moment, there is not a ship massive enough to meet the rotation requirements, and the costs associated with building, maintaining, and launching such a craft are extensive.
+In general, with the small number of negative health effects present in today's typically shorter spaceflights, as well as with the very large cost of research for a technology which is not yet really needed, the present day development of artificial gravity technology has necessarily been stunted and sporadic.  
+As the length of typical space flights increases, the need for artificial gravity for the passengers in such lengthy spaceflights will most certainly also increase, and so will the knowledge and resources available to create such artificial gravity, most likely also increase.  In summary, it is probably only a question of time, as to how long it might take before the conditions are suitable for the completion of the development of artificial gravity technology, which will almost certainly be required at some point along with the eventual and inevitable development of an increase in the average length of a spaceflight.
+
+==== In science fiction ====
+Several science fiction novels, films, and series have featured artificial gravity production.
+
+In the movie 2001: A Space Odyssey, a rotating centrifuge in the Discovery spacecraft provides artificial gravity to the astronauts within it. The entirety of Space Station 5 rotates to provide artificial 1g downforce in the shirtsleeve environment of its outer rings; the central docking hub remains closer to zero gravity.
+The 1999 television series Cowboy Bebop, a rotating ring in the Bebop spacecraft creates artificial gravity throughout the spacecraft.
+In the novel The Martian, the Hermes spacecraft achieves artificial gravity by design; it employs a ringed structure, at whose periphery forces around 40% of Earth's gravity are experienced, similar to Mars' gravity.
+In the novel Project Hail Mary by the same author, weight on the titular ship Hail Mary is provided initially by bioengine thrust, as the ship is capable of constant acceleration up to 2 ɡ and is also able to separate, turn the crew compartment inwards, and rotate to produce 1 ɡ while in orbit.
+The movie Interstellar features a spacecraft called the Endurance that can rotate on its central axis to create artificial gravity, controlled by retro thrusters on the ship.
+The 2021 film Stowaway features the upper stage of a launch vehicle connected by 450-meter long tethers to the ship's main hull, acting as a counterweight for inertia-based artificial gravity.
+The series The Expanse utilizes both rotational gravity and linear thrust gravity in various space stations and spaceships. Notably, Tycho Station and the Generation ship LDSS Nauvoo use rotational gravity. Linear gravity is provided by a fictitious 'Epstein Drive', which killed its creator Solomon Epstein during its maiden flight due to high gravity injuries.
+In the television series For All Mankind, the space hotel Polaris, later renamed Phoenix after being purchased and converted into a space vessel by Helios Aerospace for their own Mars mission, features a wheel-like structure controlled by thrusters to create artificial gravity, whilst a central axial hub operates in zero gravity as a docking station.
+
+== Linear acceleration ==

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+title: "Artificial gravity"
+chunk: 4/4
+source: "https://en.wikipedia.org/wiki/Artificial_gravity"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:12.372756+00:00"
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+---
+
+Linear acceleration is another method of generating artificial gravity, by using the thrust from a spacecraft's engines to create the illusion of being under a gravitational pull. A spacecraft under constant acceleration in a straight line would have the appearance of a gravitational pull in the direction opposite to that of the acceleration, as the thrust from the engines would cause the spacecraft to "push" itself up into the objects and persons inside of the vessel, thus creating the feeling of weight. This is because of Newton's third law: the weight that one would feel standing in a linearly accelerating spacecraft would not be a true gravitational pull, but simply the reaction of oneself pushing against the craft's hull as it pushes back. Similarly, objects that would otherwise be free-floating within the spacecraft if it were not accelerating would "fall" towards the engines when it started accelerating, as a consequence of Newton's first law: the floating object would remain at rest, while the spacecraft would accelerate towards it, and appear to an observer within that the object was "falling".
+To emulate artificial gravity on Earth, spacecraft using linear acceleration gravity may be built similar to a skyscraper, with its engines as the bottom "floor". If the spacecraft were to accelerate at the rate of 1 g—Earth's gravitational pull—the individuals inside would be pressed into the hull at the same force, and thus be able to walk and behave as if they were on Earth.
+This form of artificial gravity is desirable because it could functionally create the illusion of a gravity field that is uniform and unidirectional throughout a spacecraft, without the need for large, spinning rings, whose fields may not be uniform, not unidirectional with respect to the spacecraft, and require constant rotation. This would also have the advantage of relatively high speed: a spaceship accelerating at 1 g, 9.8 m/s2, for the first half of the journey, and then decelerating for the other half, could reach Mars within a few days. Similarly, a hypothetical space travel using constant acceleration of 1 g for one year would reach relativistic speeds and allow for a round trip to the nearest star, Proxima Centauri. As such, low-impulse but long-term linear acceleration has been proposed for various interplanetary missions. For example, even heavy (100 ton) cargo payloads to Mars could be transported to Mars in 27 months and retain approximately 55 percent of the LEO vehicle mass upon arrival into a Mars orbit, providing a low-gravity gradient to the spacecraft during the entire journey.
+This form of gravity is not without challenges, however. At present, the only practical engines that could propel a vessel fast enough to reach speeds comparable to Earth's gravitational pull require chemical reaction rockets, which expel reaction mass to achieve thrust, and thus the acceleration could only last for as long as a vessel had fuel. The vessel would also need to be constantly accelerating and at a constant speed to maintain the gravitational effect, and thus would not have gravity while stationary, and could experience significant swings in g-forces if the vessel were to accelerate above or below 1 g. Further, for point-to-point journeys, such as Earth-Mars transits, vessels would need to constantly accelerate for half the journey, turn off their engines, perform a 180° flip, reactivate their engines, and then begin decelerating towards the target destination, requiring everything inside the vessel to experience weightlessness and possibly be secured down for the duration of the flip.
+A propulsion system with a very high specific impulse (that is, good efficiency in the use of reaction mass that must be carried along and used for propulsion on the journey) could accelerate more slowly producing useful levels of artificial gravity for long periods of time. A variety of electric propulsion systems provide examples. Two examples of this long-duration, low-thrust, high-impulse propulsion that have either been practically used on spacecraft or are planned in for near-term in-space use are Hall effect thrusters and Variable Specific Impulse Magnetoplasma Rockets (VASIMR). Both provide very high specific impulse but relatively low thrust, compared to the more typical chemical reaction rockets. They are thus ideally suited for long-duration firings which would provide limited amounts of, but long-term, milli-g levels of artificial gravity in spacecraft.
+In a number of science fiction plots, acceleration is used to produce artificial gravity for interstellar spacecraft, propelled by as yet theoretical or hypothetical means.
+This effect of linear acceleration is well understood, and is routinely used for 0 g cryogenic fluid management for post-launch (subsequent) in-space firings of upper stage rockets.
+Roller coasters, especially launched roller coasters or those that rely on electromagnetic propulsion, can provide linear acceleration "gravity", and so can relatively high acceleration vehicles, such as sports cars. Linear acceleration can be used to provide air-time on roller coasters and other thrill rides.
+
+== Simulating lunar gravity ==
+
+In January 2022, China was reported by the South China Morning Post to have built a small (60 centimetres (24 in) diameter) research facility to simulate low lunar gravity with the help of magnets. The facility was reportedly partly inspired by the work of Andre Geim (who later shared the 2010 Nobel Prize in Physics for his research on graphene) and Michael Berry, who both shared the Ig Nobel Prize in Physics in 2000 for the magnetic levitation of a frog.
+
+== Graviton control or generator ==
+
+== Speculative or fictional mechanisms ==
+
+In science fiction, artificial gravity (or cancellation of gravity) or "paragravity" is sometimes present in spacecraft that are neither rotating nor accelerating. At present, there is no confirmed technique as such that can simulate gravity other than actual rotation or acceleration. There have been many claims over the years of such a device. Eugene Podkletnov, a Russian engineer, has claimed since the early 1990s to have made such a device consisting of a spinning superconductor producing a powerful "gravitomagnetic field." In 2006, a research group funded by ESA claimed to have created a similar device that demonstrated positive results for the production of gravitomagnetism, although it produced only 0.0001 g.
+
+== See also ==
+
+== References ==
+
+== External links ==
+
+List of peer review papers on artificial gravity
+TEDx talk about artificial gravity
+Overview of artificial gravity in Sci-Fi and Space Science Archived May 27, 2010, at the Wayback Machine
+NASA's Java simulation of artificial gravity
+Variable Gravity Research Facility (xGRF), concept with tethered rotating satellites, perhaps a Bigelow expandable module and a spent upper stage as a counterweight

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+---
+title: "Breakthrough Propulsion Physics Project"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Breakthrough_Propulsion_Physics_Project"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:13.631400+00:00"
+instance: "kb-cron"
+---
+
+The Breakthrough Propulsion Physics Project (BPP) was a research project funded by NASA from 1996 to 2002 to study various proposals for revolutionary methods of spacecraft propulsion that would require breakthroughs in physics before they could be realized. The project ended in 2002, when the Advanced Space Transportation Program was reorganized and all speculative research (less than Technology readiness level 3) was cancelled.
+During its six years of operational funding, this program received a total investment of $1.2 million.  
+The Breakthrough Propulsion Physics project addressed a selection of "incremental and affordable" research questions towards the overall goal of propellantless propulsion, hyperfast travel, and breakthrough propulsion methods. It selected and funded five external projects, two in-house tasks and one
+minor grant.
+At the end of the project, conclusions into fourteen topics, including these funded projects, were summarized by program manager Marc G. Millis. Of these, six research avenues were found to be nonviable, four were identified as opportunities for continued research, and four remain unresolved.
+
+
+== Non-viable approaches ==
+One in-house experiment tested the Schlicher thruster antenna, claimed by Schlicher to generate thrust.  No thrust was observed.
+Another experiment examined a gravity shielding mechanism claimed by Podkletnov and Nieminen.  Experimental investigation on the BPPP and other experiments found no evidence of the effect.
+Research on quantum tunneling was sponsored by the BPPP.  It was concluded that this is not a mechanism for faster-than-light travel.
+Other approaches categorized as non-viable are oscillation thrusters and gyroscopic antigravity, Hooper antigravity coils, and coronal blowers.
+
+
+== Unresolved approaches ==
+A theoretical examination of additional atomic energy levels (deep Dirac levels) was carried out.  Some states were ruled out, but the problem remains unsolved.
+Experiments tested Woodward's theory of inducing transient inertia by electromagnetic fields.  The small effect could not be confirmed.  Woodward continued refining the experiments and theory.  Independent experiments also remained inconclusive.
+A possible torsion-like effect in the coupling between electromagnetism and spacetime, which may ultimately be useful for propulsion, was sought in experiments. The experiments were insufficient to resolve the question.
+Other theories listed in Millis's final assessment as unresolved are Abraham–Minkowski electromagnetic momentum, interpreting inertia and gravity quantum vacuum effects, and the Podkletnov force beam.
+
+
+== Space drives ==
+One of the eight tasks funded by the BPP program was to define a strategy towards space drives.  
+As a motivation, seven examples of hypothetical space drives were described at the onset of the project.  These included the gravity-based pitch drive, bias drive, disjunction drive and diametric drive; the Alcubierre drive; and the vacuum energy based differential sail.
+The project then considered the mechanisms behind these drives.  At the end of the project, three mechanisms were identified as areas for future research.  One considers the possibility of a reaction mass in seemingly empty space, for example in dark matter, dark energy, or zero-point energy.  Another approach is to reconsider Mach's principle and Euclidean space.  A third research avenue that might ultimately prove useful for spacecraft propulsion is the coupling of fundamental forces on sub-atomic scales.
+
+
+== Quantum vacuum energy experiments ==
+One topic of investigations was the use of the zero-point energy field. As the Heisenberg uncertainty principle implies that there is no such thing as an exact amount of energy in an exact location, vacuum fluctuations are known to lead to discernible effects such as the Casimir effect. The differential sail is a speculative drive, based on the possibility of inducing differences in the pressure of vacuum fluctuations on either side of a sail-like structure — with the pressure being somehow reduced on the forward surface of the sail, but pushing as normal on the aft surface — and thus propel a vehicle forward.
+The Casimir effect was investigated experimentally and analytically under the Breakthrough Propulsion Physics project.  This included the construction of MicroElectroMechanical
+(MEM) rectangular Casimir cavities. Theoretical work showed that the effect could be used to create net forces, although the forces would be extremely small. At the conclusion of the project, the Casimir effect was categorized as an avenue for future research.
+
+
+== Legacy ==
+After funding ended, program manager Marc G. Millis was supported by NASA to complete documentation of results. The book Frontiers of Propulsion Science was published by the AIAA in February 2009, providing a deeper explanation of several propulsion methods.
+
+
+=== Tau Zero Foundation ===
+Following program cancellation in 2002, program manager Marc G. Millis and others, such as Paul Gilster (aerospace chronist and author of the website and book Centauri Dreams: Imagining and Planning for Interstellar Flight, 2004), founded the Tau Zero Foundation.
+
+
+== See also ==
+Field propulsion
+Wormhole
+
+
+== References ==

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+title: "Chandler Scientific School"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Chandler_Scientific_School"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:09.172264+00:00"
+instance: "kb-cron"
+---
+
+Abiel Chandler School of Science and the Arts was established in 1852 by Abiel Chandler, a Boston commission merchant and New Hampshire native. The school was as a separate undergraduate college at Dartmouth College comparable to the earlier Lawrence Scientific School (1847) at Harvard University and the later Sheffield Scientific School (1854) at Yale University.
+Chandler students established their own fraternities: Phi Zeta Mu (later Eta Eta chapter of Sigma Chi, now The Tabard) and Sigma Delta Pi (later Beta Theta Pi); sat in their own pews for morning services in the Old Chapel in Dartmouth Hall; and had their own sports teams.  Classes took place in Chandler Hall, which stood between Parkhurst Hall and the Blunt Alumni Center.  The building, built by Moor's Charity School in 1835 and designed by Ammi B. Young, was remodeled with a Mansard roof by Chandler mathematics professor Frank Asbury Sherman in 1871 and received a rear addition in 1898, designed by Charles Alonzo Rich, a Chandler graduate of 1876 and designing partner of the New York architects Lamb & Rich.
+Dartmouth absorbed the Chandler Scientific School in 1893 and continued as the Departments of Zoology, Botany, and Geology. The Chandler Fund continues to be administered by appointed Visitors and was valued at about $1.3 million in 2000.
+
+
+== References ==

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+title: "Cryonics"
+chunk: 1/3
+source: "https://en.wikipedia.org/wiki/Cryonics"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:15.099798+00:00"
+instance: "kb-cron"
+---
+
+Cryonics (from Greek: κρύος kryos, meaning "cold") is the low-temperature freezing (usually at −196 °C or −320.8 °F or 77.1 K) and storage of human remains in the hope that resurrection may be possible in the future. Cryonics is regarded with skepticism by the mainstream scientific community. It is generally viewed as a pseudoscience, and its practice has been characterized as quackery.
+Cryonics procedures can begin only after the "patients" are clinically and legally dead. Procedures may begin within minutes of death, and use cryoprotectants to try to prevent ice formation during cryopreservation. It is not possible to reanimate a corpse that has undergone vitrification (ultra-rapid cooling), as this damages the brain, including its neural circuits. The first corpse to be frozen was that of James Bedford, in 1967. As of 2014, remains from about 250 bodies had been cryopreserved in the United States, and 1,500 people had made arrangements for cryopreservation of theirs.
+Even if the resurrection promised by cryonics were possible, economic considerations make it unlikely cryonics corporations could remain in business long enough to deliver. The "patients", being dead, cannot continue to pay for their own preservation. Early attempts at cryonic preservation were made in the 1960s and early 1970s; most relied on family members to pay for the preservation and ended in failure, with all but one of the corpses cryopreserved before 1973 being thawed and disposed of.
+
+== Conceptual basis ==
+Cryonicists argue that as long as brain structure remains intact, there is no fundamental barrier, given our current understanding of physics, to recovering its information content. Cryonics proponents go further than the mainstream consensus in saying that the brain does not have to be continuously active to survive or retain memory. Cryonicists controversially say that a human can survive even within an inactive, badly damaged brain, as long as the original encoding of memory and personality can be adequately inferred and reconstituted from what remains.
+Cryonics uses temperatures below −130 °C, called cryopreservation, in an attempt to preserve enough brain information to permit the revival of the cryopreserved person. Cryopreservation is accomplished by freezing with or without cryoprotectant to reduce ice damage, or by vitrification to avoid ice damage. Even using the best methods, cryopreservation of whole bodies or brains is very damaging and irreversible with current technology.
+Cryonicists call the human remains packed into low-temperature vats "patients". They hope that some kind of presently nonexistent nanotechnology will be able to bring the dead back to life and treat the diseases that killed them. Mind uploading has also been proposed.
+
+== Cryonics in practice ==
+As of 2018, the cost of preparing and storing corpses using cryonics ranged from US$28,000 to $200,000.
+At high concentrations, cryoprotectants can stop ice formation completely. Cooling and solidification without crystal formation is called vitrification. In the late 1990s, cryobiologists Gregory Fahy and Brian Wowk developed the first cryoprotectant solutions that could vitrify at very slow cooling rates while still allowing whole organ survival, for the purpose of banking transplantable organs. This has allowed animal brains to be vitrified, thawed, and examined for ice damage using light and electron microscopy. No ice crystal damage was found; cellular damage was due to dehydration and toxicity of the cryoprotectant solutions.
+Costs can include payment for medical personnel to be on call for death, vitrification, transportation in dry ice to a preservation facility, and payment into a trust fund intended to cover indefinite storage in liquid nitrogen and future revival costs. As of 2011, U.S. cryopreservation costs can range from $28,000 to $200,000, and are often financed via life insurance. KrioRus, which stores bodies communally in large dewars, charges $12,000 to $36,000 for the procedure. Some customers opt to have only their brain cryopreserved ("neuropreservation"), rather than their whole body.
+As of 2014, about 250 corpses have been cryogenically preserved in the U.S., and around 1,500 people have signed up to have their remains preserved. As of 2022, five facilities retained cryopreserved bodies: three in the U.S., one in Russia, and one in Berlin.
+It seems extremely unlikely that any cryonics company could exist long enough to take advantage of the supposed benefits offered; historically, even the most robust corporations have only a one-in-a-thousand chance of lasting 100 years. Many cryonics companies have failed; as of 2018, all but one of the pre-1973 batch had gone out of business, and their stored corpses have been defrosted and disposed of.
+
+== Obstacles to success ==
+
+=== Preservation damage ===
+Medical laboratories have long used cryopreservation to maintain animal cells, human embryos, and even some organized tissues, for periods as long as three decades, but recovering large animals and organs from a frozen state is not considered possible now. Large vitrified organs tend to develop fractures during cooling, a problem worsened by the large tissue masses and very low temperatures of cryonics. Without cryoprotectants, cell shrinkage and high salt concentrations during freezing usually prevent frozen cells from functioning again after thawing. Ice crystals can also disrupt connections between cells that are necessary for organs to function.
+Some cryonics organizations use vitrification without a chemical fixation step, sacrificing some structural preservation quality for less damage at the molecular level. Some scientists, like João Pedro Magalhães, have questioned whether using a deadly chemical for fixation eliminates the possibility of biological revival, making chemical fixation unsuitable for cryonics.
+Outside of cryonics firms and cryonics-linked interest groups, many scientists are very skeptical about cryonics methods. Cryobiologist Dayong Gao has said, "we simply don't know if [subjects have] been damaged to the point where they've 'died' during vitrification because the subjects are now inside liquid nitrogen canisters." Based on experience with organ transplants, biochemist Ken Storey argues that "even if you only wanted to preserve the brain, it has dozens of different areas which would need to be cryopreserved using different protocols".

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+---
+title: "Cryonics"
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+date_saved: "2026-05-05T03:51:15.099798+00:00"
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+---
+
+=== Revival ===
+Revival would require repairing damage from lack of oxygen, cryoprotectant toxicity, thermal stress (fracturing), and freezing in tissues that do not successfully vitrify, followed by reversing the cause of death. In many cases, extensive tissue regeneration would be necessary. This revival technology remains speculative.
+
+=== Legal issues ===
+Historically, people had little control over how their bodies were treated after death, as religion held jurisdiction over the matter. Later, secular courts began to exercise jurisdiction over corpses and use discretion in carrying out deceased people's wishes. Most countries legally treat preserved bodies as deceased persons because of laws that forbid vitrifying someone who is medically alive. In France, cryonics is not considered a legal mode of body disposal; only burial, cremation, and formal body donation to science are allowed, though bodies may legally be shipped to other countries for cryonic freezing. As of 2015, British Columbia prohibits the sale of arrangements for cryonic body preservation. In Russia, cryonics falls outside both the medical industry and the funeral services industry, making it easier than in the U.S. to get hospitals and morgues to release cryonics candidates.
+In 2016, the English High Court ruled in favor of a mother's right to seek cryopreservation of her terminally ill 14-year-old daughter, as the girl wanted, contrary to the father's wishes. The decision was made on the basis that the case represented a conventional dispute over the disposal of the girl's body, although the judge urged ministers to seek "proper regulation" for the future of cryonic preservation after the hospital raised concerns about the competence and professionalism of the team that conducted the preservation procedures. In Alcor Life Extension Foundation v. Richardson, the Iowa Court of Appeals ordered the disinterment of Richardson, who was buried against his wishes, for cryopreservation.
+A detailed legal examination by Jochen Taupitz concludes that cryonic storage is legal in Germany for an indefinite period.
+
+== Ethics ==
+Writing in Bioethics in 2009, David Shaw examined cryonics. The arguments he cited against it included changing the concept of death, the expense of preservation and revival, lack of scientific advancement to permit revival, temptation to use premature euthanasia, and failure due to catastrophe. Arguments in favor of cryonics include the potential benefit to society, the prospect of immortality, and the benefits associated with avoiding death. Shaw explores the expense and the potential payoff, and applies an adapted version of Pascal's Wager to the question. He argues that someone who bets on cryonic preservation risks losing "a bit of money" but potentially gains a longer life and perhaps immortality. Shaun Pattinson responds that Shaw's calculation is incomplete because "being revived only equates to winning the wager if the revived life is worth living. A longer life of unremitting suffering, perhaps due to irreparable nerve damage or even the actions of an evil reviver, is unlikely to be considered preferable to non-revival". 
+In 2016, Charles Tandy wrote in support of cryonics, arguing that honoring someone's last wishes is seen as a benevolent duty in American and many other cultures.
+
+== History ==
+
+Cryopreservation was applied to human cells beginning in 1954 with frozen sperm, which was thawed and used to inseminate three women. The freezing of humans was first scientifically proposed by Michigan professor Robert Ettinger in The Prospect of Immortality (1962). In 1966, the first human body was frozen—though it had been embalmed for two months—by being placed in liquid nitrogen and stored at just above freezing. The middle-aged woman from Los Angeles, whose name is unknown, was soon thawed and buried by relatives.
+The first body to be cryopreserved and then frozen in hope of future revival was that of James Bedford. Alcor's Mike Darwin says Bedford's body was cryopreserved around two hours after his death by cardiorespiratory arrest (secondary to metastasized kidney cancer) on January 12, 1967. Bedford's corpse is the only one frozen before 1974 still preserved today. In 1976, Ettinger founded the Cryonics Institute; his corpse was cryopreserved in 2011. In 1981, Robert Nelson, "a former TV repairman with no scientific background" who led the Cryonics Society of California, was sued for allowing nine bodies to thaw and decompose in the 1970s; in his defense, he claimed that the Cryonics Society had run out of money. This lowered the reputation of cryonics in the U.S.
+In 2018, a Y-Combinator startup called Nectome was recognized for developing a method of preserving brains with chemicals rather than by freezing. The method is fatal, performed as euthanasia under general anesthesia, but the hope is that future technology will allow the brain to be physically scanned into a computer simulation, neuron by neuron.
+
+== Demographics ==
+According to The New York Times, cryonicists are predominantly non-religious white men, outnumbering women by about three to one. According to The Guardian, as of 2008, while most cryonicists used to be young, male, and "geeky", recent demographics have shifted slightly toward whole families.
+In 2015, Du Hong, a 61-year-old female writer of children's literature, became the first known Chinese national to have her head cryopreserved.

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+title: "Cryonics"
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+date_saved: "2026-05-05T03:51:15.099798+00:00"
+instance: "kb-cron"
+---
+
+== Reception ==
+Cryonics is generally regarded as a fringe pseudoscience. Between 1982 and November 2018, the Society for Cryobiology rejected members who practiced cryonics, and issued a public statement saying that cryonics "is an act of speculation or hope, not science", and as such outside the scope of the Society.
+Russian company KrioRus is the first non-U.S. vendor of cryonics services. Yevgeny Alexandrov, chair of the Russian Academy of Sciences commission against pseudoscience, said there was "no scientific basis" for cryonics, and that the company was based on "unfounded speculation".
+Scientists have expressed skepticism about cryonics in media sources, and the Norwegian philosopher Ole Martin Moen has written that the topic receives a "minuscule" amount of attention in academia.
+While some neuroscientists contend that all the subtleties of a human mind are contained in its anatomical structure, few will comment directly on cryonics due to its speculative nature. People who intend to be frozen are often "looked at as a bunch of kooks". Cryobiologist Kenneth B. Storey said in 2004 that cryonics is impossible and will never be possible, as cryonics proponents are proposing to "overturn the laws of physics, chemistry, and molecular science". Neurobiologist Michael Hendricks has said, "Reanimation or simulation is an abjectly false hope that is beyond the promise of technology and is certainly impossible with the frozen, dead tissue offered by the 'cryonics' industry".
+Anthropologist Simon Dein writes that cryonics is a typical pseudoscience because of its lack of falsifiability and testability. In his view, cryonics is not science, but religion: it places faith in nonexistent technology and promises to overcome death.
+William T. Jarvis has written, "Cryonics might be a suitable subject for scientific research, but marketing an unproven method to the public is quackery".
+According to cryonicist Aschwin de Wolf and others, cryonics can often produce intense hostility from spouses who are not cryonicists. James Hughes, the executive director of the pro-life-extension Institute for Ethics and Emerging Technologies, has not personally signed up for cryonics, calling it a worthy experiment but saying, "I value my relationship with my wife."
+Cryobiologist Dayong Gao has said, "People can always have hope that things will change in the future, but there is no scientific foundation supporting cryonics at this time." While it is universally agreed that personal identity is uninterrupted when brain activity temporarily ceases during incidents of accidental drowning (where people have been restored to normal functioning after being completely submerged in cold water for up to 66 minutes), one argument against cryonics is that a centuries-long absence from life might interrupt personal identity, such that the revived person would "not be themself".
+Maastricht University bioethicist David Shaw raises the argument that there would be no point in being revived in the far future if one's friends and families are dead, leaving them all alone, but he notes that family and friends can also be frozen, that there is "nothing to prevent the thawed-out freezee from making new friends", and that a lonely existence may be preferable to none at all.
+
+== In fiction ==
+
+Suspended animation is a popular subject in science fiction and fantasy settings. It is often the means by which a character is transported into the future. The characters Philip J. Fry in Futurama and Khan Noonien Singh in Star Trek exemplify this trope.
+A survey in Germany found that about half of the respondents were familiar with cryonics, and about half of those familiar with it had learned of it from films or television.
+
+== In popular culture ==
+The town of Nederland, Colorado, hosts an annual Frozen Dead Guy Days festival to commemorate a substandard attempt at cryopreservation.
+
+== Notable people ==
+
+Corpses subjected to the cryonics process include those of baseball players Ted Williams and his son John Henry Williams (in 2002 and 2004, respectively), engineer and doctor L. Stephen Coles (in 2014), economist and entrepreneur Phil Salin, and software engineer Hal Finney (in 2014).
+People known to have arranged for cryonics upon death include PayPal founders Luke Nosek and Peter Thiel, Oxford transhumanists Nick Bostrom and Anders Sandberg, and transhumanist philosopher David Pearce. Larry King once arranged for cryonics but, according to Inside Edition, changed his mind.
+Sex offender and financier Jeffrey Epstein wanted to have his head and penis frozen after death.
+The corpses of some are mistakenly believed to have undergone cryonics. The urban legend that Walt Disney's remains were cryopreserved is false; they were cremated and interred at Forest Lawn Memorial Park Cemetery. Timothy Leary was a long-time cryonics advocate and signed up with a major cryonics provider, but changed his mind shortly before his death and was not cryopreserved.
+
+== See also ==
+Aldehyde-stabilized cryopreservation
+Brain in a vat
+Cryptobiosis
+Deep hypothermic circulatory arrest
+Emergency Preservation and Resuscitation
+Embryo cryopreservation
+Extropianism
+Hibernation
+Life extension
+Organ cryopreservation
+Supercooling
+Targeted temperature management
+Tissue cryopreservation
+Technological utopianism
+
+== References ==
+
+=== Footnotes ===
+
+=== Citations ===
+
+== Further reading ==
+"Mistakes Were Made". This American Life. Episode 354. 18 April 2008. The Public Radio Exchange (PRX). WBEZ Chicago. Transcript.
+
+== External links ==

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+title: "Extraterrestrial life"
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+source: "https://en.wikipedia.org/wiki/Extraterrestrial_life"
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+
+Extraterrestrial life, or alien life (colloquially aliens), is life that originates from another world rather than on Earth. No extraterrestrial life has yet been scientifically or conclusively detected. Such life might range from simple forms such as prokaryotes to intelligent beings, possibly bringing forth civilizations that might be far more, or far less, advanced than humans. The Drake equation speculates about the existence of sapient life elsewhere in the universe. The science of extraterrestrial life is known as astrobiology.
+Speculation about inhabited worlds beyond Earth dates back to antiquity. Early Christian writers, including Augustine, discussed ideas from thinkers like Democritus and Epicurus about countless worlds in the vast universe. Pre-modern writers typically assumed extraterrestrial "worlds" were inhabited by living beings. William Vorilong, in the 15th century, acknowledged the possibility Jesus could have visited extraterrestrial worlds to redeem their inhabitants. In 1440, Nicholas of Cusa suggested Earth is a "brilliant star"; he theorized that all celestial bodies, even the Sun, could host life. Descartes wrote that there were no means to prove the stars were not inhabited by "intelligent creatures", but their existence was a matter of speculation.
+In comparison to the life-abundant Earth, the vast majority of intrasolar and extrasolar planets and moons have harsh surface conditions and disparate atmospheric chemistry, or lack an atmosphere. However, there are many extreme and chemically harsh ecosystems on Earth that do support forms of life and are often hypothesized to be the origin of life on Earth. Examples include life surrounding hydrothermal vents, acidic hot springs, and volcanic lakes, as well as halophiles and the deep biosphere.
+Since the mid-20th century, researchers have searched for extraterrestrial life and intelligence. Solar system studies focus on Venus, Mars, Europa, and Titan, while exoplanet discoveries now total 6,022 confirmed planets in 4,490 systems as of October 2025. Depending on the category of search, methods range from analysis of telescope and specimen data to radios used to detect and transmit interstellar communication. Interstellar travel remains largely hypothetical, with only the Voyager 1 and Voyager 2 probes confirmed to have entered the interstellar medium. The concept of extraterrestrial life, especially intelligent life, has greatly influenced culture and fiction. A key debate centers on contacting extraterrestrial intelligence: some advocate active attempts, while others warn it could be risky, given human history of exploiting other societies.
+
+== Context ==

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+title: "Extraterrestrial life"
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+
+Using Big Bang models for the timeline of the universe, it was too hot for life for the first 15 million years and the elements of organic life, created through stellar fusion, did not exist until at least 50 million years. The first organic compounds may have formed in the protoplanetary disk of dust grains that would eventually create rocky planets like Earth. Although Earth was in a molten state after its birth and may have burned any organics that fell on it, it would have been more receptive once it cooled down. Once the right conditions on Earth were met, life started by a chemical process known as abiogenesis.
+During most of its stellar evolution, stars combine hydrogen nuclei to make helium nuclei by stellar fusion, and the comparatively lighter weight of helium allows the star to release the extra energy. The process continues until the star uses all of its available fuel, with the speed of consumption being related to the size of the star. During its last stages, stars start combining helium nuclei to form carbon nuclei. The larger stars can further combine carbon nuclei to create oxygen and silicon, oxygen into neon and sulfur, and so on until iron. Ultimately, the star blows much of its content back into the stellar medium, where it would join clouds that would eventually become new generations of stars and planets. Many of those materials are the raw components of life on Earth. As this process takes place in all the universe, said materials are ubiquitous in the cosmos and not a rarity from the Solar System.
+Earth is a planet in the Solar System, a planetary system formed by a star at the center, the Sun, and the objects that orbit it: other planets, moons, asteroids, and comets. The sun is part of the Milky Way, a galaxy. The Milky Way is part of the Local Group, a galaxy group that is in turn part of the Laniakea Supercluster. The universe is composed of all similar structures in existence. The immense distances between celestial objects are a difficulty for studying extraterrestrial life. So far, humans have only set foot on the Moon and sent robotic probes to other planets and moons in the Solar System. Although probes can withstand conditions that may be lethal to humans, the distances cause time delays: the New Horizons took nine years after launch to reach Pluto. No probe has ever reached extrasolar planetary systems. The Voyager 2 left the Solar System at a speed of 50,000 kilometers per hour; if it headed towards the Alpha Centauri system, the closest one to Earth at 4.4 light years, it would reach it in 100,000 years. Under current technology, such systems can only be studied by telescopes, which have limitations. It is estimated that dark matter has a larger amount of combined matter than stars and gas clouds, but as it plays no role in the stellar evolution of stars and planets, it is usually not taken into account by astrobiology. 
+There is an area around a star, the circumstellar habitable zone or "Goldilocks zone", wherein water may be at the right temperature to exist in liquid form at a planetary surface. This area is neither too close to the star, where water would heated to steam, nor too far away, where water would be frozen to ice. However, although useful as an approximation, planetary habitability is complex and defined by several factors. Being in the habitable zone is not enough for a planet to be habitable, not even to actually have such liquid water. Venus is located in the solar system's habitable zone, but does not have liquid water because of the conditions of its atmosphere. In contrary, a planetary mass moon such as Europa that is beyond the circumstellar habitable zone of the Solar System has been speculated to contain liquid water under the moon’s frozen surface, as it is theorised that heat from tidal flexing causes the subsurface ocean to remain liquid. Jovian planets or gas giants are not considered habitable even if they orbit close enough to their stars as hot Jupiters, due to crushing atmospheric pressures. The actual distances for the habitable zones vary according to the type of star, and even the solar activity of each specific star influences the local habitability. The type of star also defines the time the habitable zone will exist, as its presence and limits will change along with the star's stellar evolution.
+The Big Bang occurred 13.8 billion years ago, the Solar System was formed 4.6 billion years ago, and the first hominids appeared 6 million years ago. Life on other planets may have started, evolved, given birth to extraterrestrial intelligences, and perhaps even faced a planetary extinction event millions or billions of years ago. When considered from a cosmic perspective, the brief times of existence of Earth's species may suggest that extraterrestrial life may be equally fleeting under such a scale.
+During a period of about 7 million years, from about 10 to 17 million years after the Big Bang, the background temperature was between 373 and 273 K (100 and 0 °C; 212 and 32 °F), allowing the possibility of liquid water if any planets existed. Avi Loeb (2014) speculated that primitive life might in principle have appeared during this window, which he called "the Habitable Epoch of the Early Universe".
+Life on Earth is quite ubiquitous across the planet and has adapted over time to almost all the available environments in it, extremophiles and the deep biosphere thrive at even the most hostile ones. As a result, it is inferred that life in other celestial bodies may be equally adaptive. However, the origin of life is unrelated to its ease of adaptation and may have stricter requirements. A celestial body may not have any life on it, even if it were habitable.
+
+== Likelihood of existence ==

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+
+The search and study of extraterrestrial life became a science of its own, astrobiology. Also known as exobiology, this discipline is studied by the NASA, the ESA, the INAF, and others. Astrobiology studies life from Earth as well, but with a cosmic perspective. For example, abiogenesis is of interest to astrobiology, not because of the origin of life on Earth, but for the chances of a similar process taking place in other celestial bodies. Many aspects of life, from its definition to its chemistry, are analyzed as either likely to be similar in all forms of life across the cosmos or only native to Earth. Astrobiology, however, remains constrained by the current lack of extraterrestrial life-forms to study, as all life on Earth comes from the same ancestor, and it is hard to infer general characteristics from a group with a single example to analyse.
+The 20th century came with great technological advances, speculations about future hypothetical technologies, and an increased basic knowledge of science by the general population thanks to science divulgation through the mass media. The public interest in extraterrestrial life and the lack of discoveries by mainstream science led to the emergence of pseudosciences that provided affirmative, if questionable, answers to the existence of aliens. Ufology claims that many unidentified flying objects (UFOs) would be spaceships from alien species, and ancient astronauts hypothesis claim that aliens would have visited Earth in antiquity and prehistoric times but people would have failed to understand it by then. Most UFOs or UFO sightings can be readily explained as sightings of Earth-based aircraft (including top-secret aircraft), known astronomical objects or weather phenomenons, or as hoaxes.
+Looking beyond the pseudosciences, Lewis White Beck strove to elevate the level of public discourse on the topic of extraterrestrial life by tracing the evolution of philosophical thought over the centuries from ancient times into the modern era. His review of the contributions made by Lucretius, Plutarch, Aristotle, Copernicus, Immanuel Kant, John Wilkins, Charles Darwin and Karl Marx demonstrated that even in modern times, humanity could be profoundly influenced in its search for extraterrestrial life by subtle and comforting archetypal ideas which are largely derived from firmly held religious, philosophical and existential belief systems. On a positive note, however,  Beck further argued that even if the search for extraterrestrial life proves to be unsuccessful, the endeavor itself could have beneficial consequences by assisting humanity in its attempt to actualize superior ways of living here on Earth.
+By the 21st century, it was accepted that multicellular life in the Solar System can only exist on Earth, but the interest in extraterrestrial life increased regardless. This is a result of the advances in several sciences. The knowledge of planetary habitability allows to consider on scientific terms the likelihood of finding life at each specific celestial body, as it is known which features are beneficial and harmful for life. Astronomy and telescopes also improved to the point exoplanets can be confirmed and even studied, increasing the number of search places. Life may still exist elsewhere in the Solar System in unicellular form, but the advances in spacecraft allow to send robots to study samples in situ, with tools of growing complexity and reliability. Although no extraterrestrial life has been found and life may still be just a rarity from Earth, there are scientific reasons to suspect that it can exist elsewhere, and technological advances that may detect it if it does.
+Many scientists are optimistic about the chances of finding alien life. In the words of SETI's Frank Drake, "All we know for sure is that the sky is not littered with powerful microwave transmitters". Drake noted that it is entirely possible that advanced technology results in communication being carried out in some way other than conventional radio transmission. At the same time, the data returned by space probes, and giant strides in detection methods, have allowed science to begin delineating habitability criteria on other worlds, and to confirm that at least other planets are plentiful, though aliens remain a question mark. The Wow! signal, detected in 1977 by a SETI project, remains a subject of speculative debate.
+On the other hand, other scientists are pessimistic. Jacques Monod wrote that "Man knows at last that he is alone in the indifferent immensity of the universe, whence which he has emerged by chance". In 2000, geologist and paleontologist Peter Ward and astrobiologist Donald Brownlee published a book entitled Rare Earth: Why Complex Life is Uncommon in the Universe. In it, they discussed the Rare Earth hypothesis, in which they claim that Earth-like life is rare in the universe, whereas microbial life is common. Ward and Brownlee are open to the idea of evolution on other planets that is not based on essential Earth-like characteristics such as DNA and carbon.
+As for the possible risks, theoretical physicist Stephen Hawking warned in 2010 that humans should not try to contact alien life forms. He warned that aliens might pillage Earth for resources. "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans", he said. Jared Diamond had earlier expressed similar concerns. On 20 July 2015, Hawking and Russian billionaire Yuri Milner, along with the SETI Institute, announced a well-funded effort, called the Breakthrough Initiatives, to expand efforts to search for extraterrestrial life. The group contracted the services of the 100-meter Robert C. Byrd Green Bank Telescope in West Virginia in the United States and the 64-meter Parkes Telescope in New South Wales, Australia. On 13 February 2015, scientists (including Geoffrey Marcy, Seth Shostak, Frank Drake and David Brin) at a convention of the American Association for the Advancement of Science, discussed Active SETI and whether transmitting a message to possible intelligent extraterrestrials in the Cosmos was a good idea; one result was a statement, signed by many, that a "worldwide scientific, political and humanitarian discussion must occur before any message is sent".
+
+== Government responses ==

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+
+The 1967 Outer Space Treaty and the 1979 Moon Agreement define rules of planetary protection against potentially hazardous extraterrestrial life. COSPAR also provides guidelines for planetary protection. A committee of the United Nations Office for Outer Space Affairs had in 1977 discussed for a year strategies for interacting with extraterrestrial life or intelligence. The discussion ended without any conclusions. As of 2010, the UN lacks response mechanisms for the case of an extraterrestrial contact.
+One of the NASA divisions is the Office of Safety and Mission Assurance (OSMA), also known as the Planetary Protection Office. A part of its mission is to "rigorously preclude backward contamination of Earth by extraterrestrial life."
+In 2016, the Chinese Government released a white paper detailing its space program. According to the document, one of the research objectives of the program is the search for extraterrestrial life. It is also one of the objectives of the Chinese Five-hundred-meter Aperture Spherical Telescope (FAST) program.
+In 2020, Dmitry Rogozin, the head of the Russian space agency, said the search for extraterrestrial life is one of the main goals of deep space research. 
+He also acknowledged the possibility of existence of primitive life on other planets of the Solar System.
+The French space agency has an office for the study of "non-identified aero spatial phenomena". The agency is maintaining a publicly accessible database of such phenomena, with over 1600 detailed entries. According to the head of the office, the vast majority of entries have a mundane explanation; but for 25% of entries, their extraterrestrial origin can neither be confirmed nor denied.
+In 2020, chairman of the Israel Space Agency Isaac Ben-Israel stated that the probability of detecting life in outer space is "quite large". But he disagrees with his former colleague Haim Eshed who stated that there are contacts between an advanced alien civilisation and some of Earth's governments.
+
+== In fiction ==
+
+Although the idea of extraterrestrial peoples became feasible once astronomy developed enough to understand the nature of planets, they were not thought of as being any different from humans. Having no scientific explanation for the origin of mankind and its relation to other species, there was no reason to expect them to be any other way. This was changed by the 1859 book On the Origin of Species by Charles Darwin, which proposed the theory of evolution. Now with the notion that evolution on other planets may take other directions, science fiction authors created bizarre aliens, clearly distinct from humans. A usual way to do that was to add body features from other animals, such as insects or octopuses. Costuming and special effects feasibility alongside budget considerations forced films and TV series to tone down the fantasy, but these limitations lessened since the 1990s with the advent of computer-generated imagery (CGI), and later on as CGI became more effective and less expensive.
+Real-life events sometimes captivate people's imagination and this influences the works of fiction. For example, during the Barney and Betty Hill incident, the first recorded claim of an alien abduction, the couple reported that they were abducted and experimented on by aliens with oversized heads, big eyes, pale grey skin, and small noses, a description that eventually became the grey alien archetype once used in works of fiction.
+
+== See also ==
+
+== Notes ==
+
+== References ==
+
+== Further reading ==
+
+== External links ==
+
+Astrobiology at NASA
+European Astrobiology Institute

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+---
+
+Life in the cosmos beyond Earth has never been observed, but it is expected. The hypothesis of ubiquitous extraterrestrial life relies on three main ideas. The first one, the size of the universe, allows for plenty of planets to have a similar habitability to Earth, and the age of the universe gives enough time for a long process analog to the history of Earth to happen there. The second is that the substances that make life, such as carbon and water, are ubiquitous in the universe. The third is that the physical laws are universal, which means that the forces that would facilitate or prevent the existence of life would be the same ones as on Earth. According to this argument, made by scientists such as Carl Sagan and Stephen Hawking, it would be improbable for life not to exist somewhere else other than Earth. This argument is embodied in the Copernican principle, which states that Earth does not occupy a unique position in the Universe, and the mediocrity principle, which states that there is nothing special about life on Earth.
+Other authors consider instead that life in the cosmos, or at least multicellular life, may actually be rare. The Rare Earth hypothesis maintains that life on Earth is possible because of a series of factors that range from the location in the galaxy and the configuration of the Solar System to local characteristics of the planet, and that it is unlikely that another planet simultaneously meets all such requirements. The proponents of this hypothesis consider that very little evidence suggests the existence of extraterrestrial life and that, at this point, it is just a desired result and not a reasonable scientific explanation for any gathered data.
+
+=== Drake equation ===
+In 1961, astronomer and astrophysicist Frank Drake devised the Drake equation as a way to stimulate scientific dialogue at a meeting on the search for extraterrestrial intelligence (SETI). The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy. The Drake equation is:
+
+  
+    
+      
+        N
+        =
+        
+          R
+          
+            ∗
+          
+        
+        ⋅
+        
+          f
+          
+            p
+          
+        
+        ⋅
+        
+          n
+          
+            e
+          
+        
+        ⋅
+        
+          f
+          
+            ℓ
+          
+        
+        ⋅
+        
+          f
+          
+            i
+          
+        
+        ⋅
+        
+          f
+          
+            c
+          
+        
+        ⋅
+        L
+      
+    
+    {\displaystyle N=R_{\ast }\cdot f_{p}\cdot n_{e}\cdot f_{\ell }\cdot f_{i}\cdot f_{c}\cdot L}
+  
+
+where:
+
+N = the number of Milky Way galaxy civilizations communicating across interplanetary space
+and
+
+R* = the rate of formation of stars suitable for intelligent life in our galaxy
+fp = the fraction of those stars that have planets
+ne = the average number of planets that can potentially support life
+fl = the fraction of planets that actually support life
+fi = the fraction of planets with life that evolves to become intelligent life (civilisations)
+fc = the fraction of civilizations that develop a technology to broadcast detectable signs of their existence into space
+L = the length of time over which such civilizations broadcast detectable signals into space
+Drake's proposed estimates are as follows, but numbers on the right side of the equation are agreed as speculative and open to substitution:
+
+  
+    
+      
+        10,000
+        =
+        5
+        ⋅
+        0.5
+        ⋅
+        2
+        ⋅
+        1
+        ⋅
+        0.2
+        ⋅
+        1
+        ⋅
+        10,000
+      
+    
+    {\displaystyle 10{,}000=5\cdot 0.5\cdot 2\cdot 1\cdot 0.2\cdot 1\cdot 10{,}000}
+  
+
+The Drake equation has proved controversial since, although it is written as a math equation, none of its values were known at the time. Although some values may eventually be measured, others are based on social sciences and are not knowable by their very nature. This does not allow one to make noteworthy conclusions from the equation.
+Based on observations from the Hubble Space Telescope, there are nearly 2 trillion galaxies in the observable universe. It is estimated that at least ten percent of all Sun-like stars have a system of planets. In other words, there are 6.25×1018 stars with planets orbiting them in the observable universe. Even if it is assumed that only one out of a billion of these stars has planets supporting life, there would be some 6.25 billion life-supporting planetary systems in the observable universe. A 2013 study based on results from the Kepler spacecraft estimated that the Milky Way contains at least as many planets as it does stars, resulting in 100–400 billion exoplanets. The Nebular hypothesis that explains the formation of the Solar System and other planetary systems would suggest that those can have several configurations, and not all of them may have rocky planets within the habitable zone. 
+The apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilisations and the lack of evidence for such civilisations is known as the Fermi paradox. Dennis W. Sciama claimed that life's existence in the universe depends on various fundamental constants. Zhi-Wei Wang and Samuel L. Braunstein suggest that a random universe capable of supporting life is likely to be just barely able to do so, giving a potential explanation to the Fermi paradox.
+
+== Biochemical basis ==

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+---
+title: "Extraterrestrial life"
+chunk: 4/12
+source: "https://en.wikipedia.org/wiki/Extraterrestrial_life"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:16.499650+00:00"
+instance: "kb-cron"
+---
+
+If extraterrestrial life exists, it could range from simple microorganisms and multicellular organisms similar to animals or plants, to complex alien intelligences akin to humans. When scientists talk about extraterrestrial life, they consider all those types. Although it is possible that extraterrestrial life may have other configurations, scientists use the hierarchy of lifeforms from Earth for simplicity, as it is the only one known to exist.
+The first basic requirement for life is an environment with non-equilibrium thermodynamics, which means that the thermodynamic equilibrium must be broken by a source of energy. The traditional sources of energy in the cosmos are the stars, such as for life on Earth, which depends on the energy of the sun. However, there are other alternative energy sources, such as volcanoes, plate tectonics, and hydrothermal vents. There are ecosystems on Earth in deep areas of the ocean that do not receive sunlight, and take energy from black smokers instead. Magnetic fields and radioactivity have also been proposed as sources of energy, although they would be less efficient ones.
+Life on Earth requires water in a liquid state as a solvent in which biochemical reactions take place. It is highly unlikely that an abiogenesis process can start within a gaseous or solid medium: the atom speeds, either too fast or too slow, make it difficult for specific ones to meet and start chemical reactions. A liquid medium also allows the transport of nutrients and substances required for metabolism. Sufficient quantities of carbon and other elements, along with water, might enable the formation of living organisms on terrestrial planets with a chemical make-up and temperature range similar to that of Earth. Life based on ammonia rather than water has been suggested as an alternative, though this solvent appears less suitable than water. It is also conceivable that there are forms of life whose solvent is a liquid hydrocarbon, such as methane, ethane or propane.
+Another unknown aspect of potential extraterrestrial life would be the chemical elements that would compose it. Life on Earth is largely composed of carbon, but there could be other hypothetical types of biochemistry. A replacement for carbon would need to be able to create complex molecules, store information required for evolution, and be freely available in the medium. To create DNA, RNA, or a close analog, such an element should be able to bind its atoms with many others, creating complex and stable molecules. It should be able to create at least three covalent bonds: two for making long strings and at least a third to add new links and allow for diverse information. Only nine elements meet this requirement: boron, nitrogen, phosphorus, arsenic, antimony (three bonds), carbon, silicon, germanium and tin (four bonds). As for abundance, carbon, nitrogen, and silicon are the most abundant ones in the universe, far more than the others. On Earth's crust the most abundant of those elements is silicon, in the Hydrosphere it is carbon and in the atmosphere, it is carbon and nitrogen. Silicon, however, has disadvantages over carbon. The molecules formed with silicon atoms are less stable, and more vulnerable to acids, oxygen, and light. An ecosystem of silicon-based lifeforms would require very low temperatures, high atmospheric pressure, an atmosphere devoid of oxygen, and a solvent other than water. The low temperatures required would add an extra problem, the difficulty to kickstart a process of abiogenesis to create life in the first place. Norman Horowitz, head of the Jet Propulsion Laboratory bioscience section for the Mariner and Viking missions from 1965 to 1976 considered that the great versatility of the carbon atom makes it the element most likely to provide solutions, even exotic solutions, to the problems of survival of life on other planets.  However, he also considered that the conditions found on Mars were incompatible with carbon based life. 
+Even if extraterrestrial life is based on carbon and uses water as a solvent, like Earth life, it may still have a radically different biochemistry.  Life is generally considered to be a product of natural selection.  It has been proposed that to undergo natural selection a living entity must have the capacity to replicate itself, the capacity to avoid damage/decay, and the capacity to acquire and process resources in support of the first two capacities. Life on Earth may have started with an RNA world and later evolved to its current form, where some of the RNA tasks were transferred to DNA and proteins. Extraterrestrial life may still be stuck using RNA, or evolve into other configurations. It is unclear if our biochemistry is the most efficient one that could be generated, or which elements would follow a similar pattern. However, it is likely that, even if cells had a different composition to those from Earth, they would still have a cell membrane. Life on Earth jumped from prokaryotes to eukaryotes and from unicellular organisms to multicellular organisms through evolution. So far no alternative process to achieve such a result has been conceived, even if hypothetical. Evolution requires life to be divided into individual organisms, and no alternative organisation has been satisfactorily proposed either. At the basic level, membranes define the limit of a cell, between it and its environment, while remaining partially open to exchange energy and resources with it.
+The evolution from simple cells to eukaryotes, and from them to multicellular lifeforms, is not guaranteed. The Cambrian explosion took place thousands of millions of years after the origin of life, and its causes are not fully known yet. On the other hand, the jump to multicellularity took place several times, which suggests that it could be a case of convergent evolution, and so likely to take place on other planets as well. Palaeontologist Simon Conway Morris considers that convergent evolution would lead to kingdoms similar to our plants and animals, and that many features are likely to develop in alien animals as well, such as bilateral symmetry, limbs, digestive systems and heads with sensory organs. Scientists from the University of Oxford analysed it from the perspective of evolutionary theory and wrote in a study in the International Journal of Astrobiology that aliens may be similar to humans. The planetary context would also have an influence: a planet with higher gravity would have smaller animals, and other types of stars can lead to non-green photosynthesizers. The amount of energy available would also affect biodiversity, as an ecosystem sustained by black smokers or hydrothermal vents would have less energy available than those sustained by a star's light and heat, and so its lifeforms would not grow beyond a certain complexity. There is also research in assessing the capacity of life for developing intelligence. It has been suggested that this capacity arises with the number of potential niches a planet contains, and that the complexity of life itself is reflected in the information density of planetary environments, which in turn can be computed from its niches.

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+---
+title: "Extraterrestrial life"
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+source: "https://en.wikipedia.org/wiki/Extraterrestrial_life"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:16.499650+00:00"
+instance: "kb-cron"
+---
+
+=== Harsh environmental conditions on Earth harboring life ===
+It is common knowledge that the conditions on other planets in the solar system, in addition to the many galaxies outside of the Milky Way galaxy, are very harsh and seem to be too extreme to harbor any life. The environmental conditions on these planets can have intense UV radiation paired with extreme temperatures, lack of water, and much more that can lead to conditions that don't seem to favor the creation or maintenance of extraterrestrial life. However, there has been much historical evidence that some of the earliest and most basic forms of life on Earth originated in some extreme environments that seem unlikely to have harbored life at least at one point in Earth's history. Fossil evidence as well as many historical theories backed up by years of research and studies have marked environments like hydrothermal vents or acidic hot springs as some of the first places that life could have originated on Earth. These environments can be considered extreme when compared to the typical ecosystems that the majority of life on Earth now inhabit, as hydrothermal vents are scorching hot due to the magma escaping from the Earth's mantle and meeting the much colder oceanic water. Even in today's world, there can be a diverse population of bacteria found inhabiting the area surrounding these hydrothermal vents which can suggest that some form of life can be supported even in the harshest of environments like the other planets in the solar system.
+The aspects of these harsh environments that make them ideal for the origin of life on Earth, as well as the possibility of creation of life on other planets, is the chemical reactions forming spontaneously. For example, the hydrothermal vents found on the ocean floor are known to support many chemosynthetic processes which allow organisms to utilize energy through reduced chemical compounds that fix carbon. In return, these reactions will allow for organisms to live in relatively low oxygenated environments while maintaining enough energy to support themselves. The early Earth environment was reducing and therefore, these carbon fixing compounds were necessary for the survival and possible origin of life on Earth. With the little amount of information that scientists have found regarding the atmosphere on other planets in the Milky Way galaxy and beyond, the atmospheres are most likely reducing or with very low oxygen levels, especially when compared with Earth's atmosphere. If there were the necessary elements and ions on these planets, the same carbon fixing, reduced chemical compounds occurring around hydrothermal vents could also occur on these planets' surfaces and possibly result in the origin of extraterrestrial life.
+
+== Planetary habitability in the Solar System ==

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+---
+title: "Extraterrestrial life"
+chunk: 6/12
+source: "https://en.wikipedia.org/wiki/Extraterrestrial_life"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:16.499650+00:00"
+instance: "kb-cron"
+---
+
+ 
+The Solar System has a wide variety of planets, dwarf planets, and moons, and each one is studied for its potential to host life. Each one has its own specific conditions that may benefit or harm life. So far, the only lifeforms found are those from Earth. No extraterrestrial intelligence other than humans exists or has ever existed within the Solar System. Astrobiologist Mary Voytek points out that it would be unlikely to find large ecosystems, as they would have already been detected by now.
+The inner Solar System is likely devoid of life. However, Venus is still of interest to astrobiologists, as it is a terrestrial planet that was likely similar to Earth in its early stages and developed in a different way. There is a greenhouse effect, the surface is the hottest in the Solar System, sulfuric acid clouds, all surface liquid water is lost, and it has a thick carbon-dioxide atmosphere with huge pressure. Comparing both helps to understand the precise differences that lead to beneficial or harmful conditions for life. And despite the conditions against life on Venus, there are suspicions that microbial life-forms may still survive in high-altitude clouds.
+Mars is a cold and almost airless desert, inhospitable to life. However, recent studies revealed that water on Mars used to be quite abundant, forming rivers, lakes, and perhaps even oceans. Mars may have been habitable back then, and life on Mars may have been possible. But when the planetary core ceased to generate a magnetic field, solar winds removed the atmosphere and the planet became vulnerable to solar radiation. Ancient life-forms may still have left fossilised remains, and microbes may still survive deep underground.
+As mentioned, the gas giants and ice giants are unlikely to contain life. The most distant solar system bodies, found in the Kuiper Belt and outwards, are locked in permanent deep-freeze, but cannot be ruled out completely.
+Although the giant planets themselves are highly unlikely to have life, there is much hope to find it on moons orbiting these planets. Europa, from the Jovian system, has a subsurface ocean below a thick layer of ice. Ganymede and Callisto also have subsurface oceans, but life is less likely in them because water is sandwiched between layers of solid ice. Europa would have contact between the ocean and the rocky surface, which helps the chemical reactions. It may be difficult to dig so deep in order to study those oceans, though. Enceladus, a tiny moon of Saturn with another subsurface ocean, may not need to be dug, as it releases water to space in eruption columns. The space probe Cassini flew inside one of these, but could not make a full study because NASA did not expect this phenomenon and did not equip the probe to study ocean water. Still, Cassini detected complex organic molecules, salts, evidence of hydrothermal activity, hydrogen, and methane.
+Titan is the only celestial body in the Solar System besides Earth that has liquid bodies on the surface. It has rivers, lakes, and rain of hydrocarbons, methane, and ethane, and even a cycle similar to Earth's water cycle. This special context encourages speculations about lifeforms with different biochemistry, but the cold temperatures would make such chemistry take place at a very slow pace. Water is rock-solid on the surface, but Titan does have a subsurface water ocean like several other moons. However, it is of such a great depth that it would be very difficult to access it for study.
+
+== Scientific search ==
+
+The science that searches and studies life in the universe, both on Earth and elsewhere, is called astrobiology. With the study of Earth's life, the only known form of life, astrobiology seeks to study how life starts and evolves and the requirements for its continuous existence. This helps to determine what to look for when searching for life in other celestial bodies. This is a complex area of study, and uses the combined perspectives of several scientific disciplines, such as astronomy, biology, chemistry, geology, oceanography, and atmospheric sciences.
+The scientific search for extraterrestrial life is being carried out both directly and indirectly. As of 23 April 2026, there are 6,273 confirmed exoplanets in 4,694 planetary systems, with 1,049 systems having more than one planet.  Other planets and moons in the Solar System hold the potential for hosting primitive life such as microorganisms. As of 8 February 2021, an updated status of studies considering the possible detection of lifeforms on Venus (via phosphine) and Mars (via methane) was reported.
+
+=== Search for basic life ===

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+---
+title: "Extraterrestrial life"
+chunk: 7/12
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+category: "reference"
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+date_saved: "2026-05-05T03:51:16.499650+00:00"
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+---
+
+Scientists search for biosignatures within the Solar System by studying planetary surfaces and examining meteorites. Some claim to have identified evidence that microbial life has existed on Mars. In 1996, a controversial report stated that structures resembling nanobacteria were discovered in a meteorite, ALH84001, formed of rock ejected from Mars. Although all the unusual properties of the meteorite were eventually explained as the result of inorganic processes, the controversy over its discovery laid the groundwork for the development of astrobiology.
+An experiment on the two Viking Mars landers reported gas emissions from heated Martian soil samples that some scientists argue are consistent with the presence of living microorganisms. Lack of corroborating evidence from other experiments on the same samples suggests that a non-biological reaction is a more likely hypothesis.
+In February 2005 NASA scientists reported they may have found some evidence of extraterrestrial life on Mars. The two scientists, Carol Stoker and Larry Lemke of NASA's Ames Research Center, based their claim on methane signatures found in Mars's atmosphere resembling the methane production of some forms of primitive life on Earth, as well as on their own study of primitive life near the Rio Tinto river in Spain. NASA officials soon distanced NASA from the scientists' claims, and Stoker herself backed off from her initial assertions.
+In November 2011, NASA launched the Mars Science Laboratory that landed the Curiosity rover on Mars. It is designed to assess the past and present habitability on Mars using a variety of scientific instruments. The rover landed on Mars at Gale Crater in August 2012.
+A group of scientists at Cornell University started a catalog of microorganisms, with the way each one reacts to sunlight. The goal is to help with the search for similar organisms in exoplanets, as the starlight reflected by planets rich in such organisms would have a specific spectrum, unlike that of starlight reflected from lifeless planets. If Earth was studied from afar with this system, it would reveal a shade of green, as a result of the abundance of plants with photosynthesis.
+In August 2011, NASA studied meteorites found on Antarctica, finding adenine, guanine, hypoxanthine, and xanthine. Adenine and guanine are components of DNA, and the others are used in other biological processes. The studies ruled out pollution of the meteorites on Earth, as those components would not be freely available the way they were found in the samples. This discovery suggests that several organic molecules that serve as building blocks of life may be generated within asteroids and comets. In October 2011, scientists reported that cosmic dust contains complex organic compounds ("amorphous organic solids with a mixed aromatic-aliphatic structure") that could be created naturally, and rapidly, by stars. It is still unclear if those compounds played a role in the creation of life on Earth, but Sun Kwok, of the University of Hong Kong, thinks so. "If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life."
+In August 2012, and in a world first, astronomers at Copenhagen University reported the detection of a specific sugar molecule, glycolaldehyde, in a distant star system. The molecule was found around the protostellar binary IRAS 16293-2422, which is located 400 light years from Earth. Glycolaldehyde is needed to form ribonucleic acid, or RNA, which is similar in function to DNA. This finding suggests that complex organic molecules may form in stellar systems prior to the formation of planets, eventually arriving on young planets early in their formation.
+In December 2023, astronomers reported the first time discovery, in the plumes of Enceladus, moon of the planet Saturn, of hydrogen cyanide, a possible chemical essential for life as we know it, as well as other organic molecules, some of which are yet to be better identified and understood. According to the researchers, "these [newly discovered] compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life."
+
+=== Search for extraterrestrial intelligences ===

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+title: "Extraterrestrial life"
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+category: "reference"
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+date_saved: "2026-05-05T03:51:16.499650+00:00"
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+---
+
+Although most searches are focused on the biology of extraterrestrial life, an extraterrestrial intelligence capable enough to develop a civilization may be detectable by other means as well. Technology may generate technosignatures, effects on the native planet that may not be caused by natural causes. There are three main types of techno-signatures considered: interstellar communications, effects on the atmosphere, and planetary-sized structures such as Dyson spheres.
+Organizations such as the SETI Institute search the cosmos for potential forms of communication. They started with radio waves, and now search for laser pulses as well. The challenge for this search is that there are natural sources of such signals as well, such as gamma-ray bursts and supernovae, and the difference between a natural signal and an artificial one would be in its specific patterns. Astronomers intend to use artificial intelligence for this, as it can manage large amounts of data and is devoid of biases and preconceptions. Besides, even if there is an advanced extraterrestrial civilization, there is no guarantee that it is transmitting radio communications in the direction of Earth. The length of time required for a signal to travel across space means that a potential answer may arrive decades or centuries after the initial message.
+The atmosphere of Earth is rich in nitrogen dioxide as a result of air pollution, which can be detectable. The natural abundance of carbon, which is also relatively reactive, makes it likely to be a basic component of the development of a potential extraterrestrial technological civilization, as it is on Earth. Fossil fuels may likely be generated and used on such worlds as well. The abundance of chlorofluorocarbons in the atmosphere can also be a clear technosignature, considering their role in ozone depletion. Light pollution may be another technosignature, as multiple lights on the night side of a rocky planet can be a sign of advanced technological development. However, modern telescopes are not strong enough to study exoplanets with the required level of detail to perceive it.
+The Kardashev scale proposes that a civilization may eventually start consuming energy directly from its local star. This would require giant structures built next to it, called Dyson spheres. Those speculative structures would cause an excess infrared radiation, that telescopes may notice. The infrared radiation is typical of young stars, surrounded by dusty protoplanetary disks that will eventually form planets. An older star such as the Sun would have no natural reason to have excess infrared radiation. The presence of heavy elements in a star's light-spectrum is another potential biosignature; such elements would (in theory) be found if the star were being used as an incinerator/repository for nuclear waste products.
+
+=== Extrasolar planets ===
+
+Some astronomers search for extrasolar planets that may be conducive to life, narrowing the search to terrestrial planets within the habitable zones of their stars. Since 1992, over four thousand exoplanets have been discovered (6,416 planets in 4,809 planetary systems including 1,061 multiple planetary systems as of 23 April 2026).
+The extrasolar planets so far discovered range in size from that of terrestrial planets similar to Earth's size to that of gas giants larger than Jupiter. The number of observed exoplanets is expected to increase greatly in the coming years. The Kepler space telescope has also detected a few thousand candidate planets, of which about 11% may be false positives.
+There is at least one planet on average per star. About 1 in 5 Sun-like stars have an "Earth-sized" planet in the habitable zone, with the nearest expected to be within 12 light-years distance from Earth. Assuming 200 billion stars in the Milky Way, that would be 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if red dwarfs are included. The rogue planets in the Milky Way possibly number in the trillions.
+The nearest known exoplanet is Proxima Centauri b, located 4.2 light-years (1.3 pc) from Earth in the southern constellation of Centaurus.
+As of March 2014, the least massive exoplanet known is PSR B1257+12 A, which is about twice the mass of the Moon. The most massive planet listed on the NASA Exoplanet Archive is DENIS-P J082303.1−491201 b, about 29 times the mass of Jupiter, although according to most definitions of a planet, it is too massive to be a planet and may be a brown dwarf instead. Almost all of the planets detected so far are within the Milky Way, but there have also been a few possible detections of extragalactic planets. The study of planetary habitability also considers a wide range of other factors in determining the suitability of a planet for hosting life.
+One sign that a planet probably already contains life is the presence of an atmosphere with significant amounts of oxygen, since that gas is highly reactive and generally would not last long without constant replenishment. This replenishment occurs on Earth through photosynthetic organisms. One way to analyse the atmosphere of an exoplanet is through spectrography when it transits its star, though this might only be feasible with dim stars like white dwarfs.
+
+== History and cultural impact ==
+
+=== Cosmic pluralism ===

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+title: "Extraterrestrial life"
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+date_saved: "2026-05-05T03:51:16.499650+00:00"
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+---
+
+The modern concept of extraterrestrial life is based on assumptions that were not commonplace during the early days of astronomy. The first explanations for the celestial objects seen in the night sky were based on mythology. Scholars from Ancient Greece were the first to consider that the universe is inherently understandable and rejected explanations based on supernatural incomprehensible forces, such as the myth of the Sun being pulled across the sky in the chariot of Apollo. They had not developed the scientific method yet and based their ideas on pure thought and speculation, but they developed precursor ideas to it, such as that explanations had to be discarded if they contradict observable facts. The discussions of those Greek scholars established many of the pillars that would eventually lead to the idea of extraterrestrial life, such as Earth being round and not flat. The cosmos was first structured in a geocentric model that considered that the sun and all other celestial bodies revolve around Earth. However, they did not consider them as worlds. In Greek understanding, the world was composed by both Earth and the celestial objects with noticeable movements. Anaximander thought that the cosmos was made from apeiron, a substance that created the world, and that the world would eventually return to the cosmos.
+Eventually two groups emerged, the atomists that thought that matter at both Earth and the cosmos was equally made of small atoms of the classical elements (earth, water, fire and air), and the Aristotelians who thought that those elements were exclusive of Earth and that the cosmos was made of a fifth one, the aether. Atomist Epicurus thought that the processes that created the world, its animals and plants should have created other worlds elsewhere, along with their own animals and plants. Aristotle thought instead that all the earth element naturally fell towards the center of the universe, and that would make it impossible for other planets to exist elsewhere. Under that reasoning, Earth was not only in the center, it was also the only planet in the universe.
+Cosmic pluralism, the plurality of worlds, or simply pluralism, describes the philosophical belief in numerous "worlds" in addition to Earth, which might harbor extraterrestrial life. The earliest recorded assertion of extraterrestrial human life is found in ancient scriptures of Jainism. There are multiple "worlds" mentioned in Jain scriptures that support human life. These include, among others, Bharat Kshetra, Mahavideh Kshetra, Airavat Kshetra, and Hari kshetra. Medieval Muslim writers like Fakhr al-Din al-Razi and Muhammad al-Baqir supported cosmic pluralism on the basis of the Qur'an. Chaucer's poem The House of Fame engaged in medieval thought experiments that postulated the plurality of worlds. However, those ideas about other worlds were different from the current knowledge about the structure of the universe, and did not postulate the existence of planetary systems other than the Solar System. When those authors talk about other worlds, they talk about places located at the center of their own systems, and with their own stellar vaults and cosmos surrounding them.
+The Greek ideas and the disputes between atomists and Aristotelians outlived the fall of the Greek empire. The Great Library of Alexandria compiled information about it, part of which was translated by Islamic scholars and thus survived the end of the Library. Baghdad combined the knowledge of the Greeks, the Indians, the Chinese and its own scholars, and the knowledge expanded through the Byzantine Empire. From there it eventually returned to Europe by the time of the Middle Ages. However, as the Greek atomist doctrine held that the world was created by random movements of atoms, with no need for a creator deity, it became associated with atheism, and the dispute intertwined with religious ones. Still, the Church did not react to those topics in a homogeneous way, and there were stricter and more permissive views within the church itself.
+The first known mention of the term 'panspermia' was in the writings of the 5th-century BC Greek philosopher Anaxagoras. He proposed the idea that life exists everywhere.
+
+=== Early modern period ===

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+title: "Extraterrestrial life"
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+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:16.499650+00:00"
+instance: "kb-cron"
+---
+
+By the time of the late Middle Ages there were many known inaccuracies in the geocentric model, but it was kept in use because naked eye observations provided limited data. Nicolaus Copernicus started the Copernican Revolution by proposing that the planets revolve around the sun rather than Earth. His proposal had little acceptance at first because, as he kept the assumption that orbits were perfect circles, his model led to as many inaccuracies as the geocentric one. Tycho Brahe improved the available data with naked-eye observatories, which worked with highly complex sextants and quadrants. Tycho could not make sense of his observations, but Johannes Kepler did: orbits were not perfect circles, but ellipses. This knowledge benefited the Copernican model, which worked now almost perfectly. The invention of the telescope a short time later, perfected by Galileo Galilei, clarified the final doubts, and the paradigm shift was completed. Under this new understanding, the notion of extraterrestrial life became feasible: if Earth is but just a planet orbiting around a star, there may be planets similar to Earth elsewhere. The astronomical study of distant bodies also proved that physical laws are the same elsewhere in the universe as on Earth, with nothing making the planet truly special.
+The new ideas were met with resistance from the Catholic church. Galileo was tried for the heliocentric model, which was considered heretical, and forced to recant it. The best-known early-modern proponent of ideas of extraterrestrial life was the Italian philosopher Giordano Bruno, who argued in the 16th century for an infinite universe in which every star is surrounded by its own planetary system. Bruno wrote that other worlds "have no less virtue nor a nature different to that of our earth" and, like Earth, "contain animals and inhabitants". Bruno's belief in the plurality of worlds was one of the charges leveled against him by the Venetian Holy Inquisition, which tried and executed him.
+The heliocentric model was further strengthened by the postulation of the theory of gravity by Sir Isaac Newton. This theory provided the mathematics that explains the motions of all things in the universe, including planetary orbits. By this point, the geocentric model was definitely discarded. By this time, the use of the scientific method had become a standard, and new discoveries were expected to provide evidence and rigorous mathematical explanations. Science also took a deeper interest in the mechanics of natural phenomena, trying to explain not just the way nature works but also the reasons for working that way.
+There was very little actual discussion about extraterrestrial life before this point, as the Aristotelian ideas remained influential while geocentrism was still accepted. When it was finally proved wrong, it not only meant that Earth was not the center of the universe, but also that the lights seen in the sky were not just lights, but physical objects. The notion that life may exist in them as well soon became an ongoing topic of discussion, although one with no practical ways to investigate.
+The possibility of extraterrestrials remained a widespread speculation as scientific discovery accelerated. William Herschel, the discoverer of Uranus, was one of many 18th–19th-century astronomers who believed that the Solar System is populated by alien life. Other scholars of the period who championed "cosmic pluralism" included Immanuel Kant and Benjamin Franklin. At the height of the Enlightenment, even the Sun and Moon were considered candidates for extraterrestrial inhabitants.
+
+=== 19th century ===
+
+Speculation about life on Mars increased in the late 19th century, following telescopic observation of apparent Martian canals – which soon, however, turned out to be optical illusions. Despite this, in 1895, American astronomer Percival Lowell published his book Mars, followed by Mars and its Canals in 1906, proposing that the canals were the work of a long-gone civilisation. 
+Spectroscopic analysis of Mars's atmosphere began in earnest in 1894, when U.S. astronomer William Wallace Campbell showed that neither water nor oxygen was present in the Martian atmosphere. By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis.
+As a consequence of the belief in the spontaneous generation there was little thought about the conditions of each celestial body: it was simply assumed that life would thrive anywhere. This theory was disproved by Louis Pasteur in the 19th century. Popular belief in thriving alien civilisations elsewhere in the solar system still remained strong until Mariner 4 and Mariner 9 provided close images of Mars, which debunked forever the idea of the existence of Martians and decreased the previous expectations of finding alien life in general. The end of the spontaneous generation belief forced investigation into the origin of life. Although abiogenesis is the more accepted theory, a number of authors reclaimed the term "panspermia" and proposed that life was brought to Earth from elsewhere. Some of those authors are Jöns Jacob Berzelius (1834), Kelvin (1871), Hermann von Helmholtz (1879) and, somewhat later, by Svante Arrhenius (1903).
+The science fiction genre, although not so named during the time, developed during the late 19th century. The expansion of the genre of extraterrestrials in fiction influenced the popular perception over the real-life topic, making people eager to jump to conclusions about the discovery of aliens. Science marched at a slower pace, some discoveries fueled expectations and others dashed excessive hopes. For example, with the advent of telescopes, most structures seen on the Moon or Mars were immediately attributed to Selenites or Martians, and later ones (such as more powerful telescopes) revealed that all such discoveries were natural features. A famous case is the Cydonia region of Mars, first imaged by the Viking 1 orbiter. The low-resolution photos showed a rock formation that resembled a human face, but later spacecraft took photos in higher detail that showed that there was nothing special about the site.
+
+=== Recent history ===

data/en.wikipedia.org/wiki/Magmatic_water-0.md

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+---
+title: "Magmatic water"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Magmatic_water"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:04.106847+00:00"
+instance: "kb-cron"
+---
+
+Magmatic water, also known as juvenile water, is an aqueous phase in equilibrium with minerals that have been dissolved by magma deep within the Earth's crust and is released to the atmosphere during a volcanic eruption. It plays a key role in assessing the crystallization of igneous rocks, particularly silicates, as well as the rheology and evolution of magma chambers. Magma is composed of minerals, crystals and volatiles in varying relative natural abundance. Magmatic differentiation varies significantly based on various factors, most notably the presence of water. An abundance of volatiles within magma chambers decreases viscosity and leads to the formation of minerals bearing halogens, including chloride and hydroxide groups. In addition, the relative abundance of volatiles varies within basaltic, andesitic, and rhyolitic magma chambers, leading to some volcanoes being exceedingly more explosive than others. Magmatic water is practically insoluble in silicate melts but has demonstrated the highest solubility within rhyolitic melts. An abundance of magmatic water has been shown to lead to high-grade deformation, as a result of altering the composition of hydrogen isotope biogeochemistry (δ2H) and stable oxygen isotope ratios (δ18O) within host rocks.
+
+
+== Composition ==
+Magma exists in three main forms that vary in composition. When magma crystallizes within the crust, it forms an extrusive igneous rock. Dependent on the composition of the magma, it may form either rhyolite, andesite, or basalt. Volatiles, particularly water and carbon dioxide, significantly impact the behavior of each form of magma differently., Magma with a high concentration of volatiles has a significant reduction in temperature of up to hundreds of degrees, which reduces its inherent viscosity. The behavior of magma is also altered by varying mineralogic compositions, which is noted in Figure 1. For instance, magmatic water leads to the crystallization of several minerals abundant in hydroxyl- or halogenated-groups, including garnets. Analyses of these minerals can be used to analyze the conditions of formation in the interior of rocky planets.,
+
+
+=== Volatiles ===
+Volatiles are present in nearly all magma in different concentrations. Examples of volatiles within magma include water, carbon dioxide, and halogen gases. High pressures allow these volatiles to stay relatively stable within solution. However, over time, as the magmatic pressure decreases, volatiles will rise out of solution in the gaseous phase, further decreasing the magmatic pressure. These pressure differences cause drastic differences in the volume of a magma. Pressure difference causes some forms of volcanoes to be highly explosive and others to be effusive.
+
+
+=== Mineralogy ===
+An example of a mineral containing hydroxyl groups is garnet. Garnet is an anhydrous mineral commonly analyzed within geological subdisciplines because of its general stability. One study analyzed the presence of garnets within the upper mantle through infrared spectroscopy and showed absorption at approximately 3500 cm−1, which is consistent with the presence of hydroxyl groups. These garnets have been shown to vary in composition dependent on its geographic origin. One particular study in Southern Africa determined concentrations ranging from 1 ppm - 135 ppm. However, this is significantly lower than the hydroxyl content in regions such as the Colorado Plateau. It was also demonstrated that there is an inverse correlation regarding the concentration of OH and Mg + Fe.
+
+
+=== Basaltic magma ===
+Basaltic magma is the most abundant in iron, magnesium, and calcium but the lowest in silica, potassium, and sodium.,  The composition of silica within basaltic magma ranges from 45-55 weight percent (wt.%), or mass fraction of a species. It forms in temperatures ranging from approximately 1830 °F to 2200 °F.,  Basaltic magma has the lowest viscosity and volatiles content, yet still may be up to 100,000 times more viscous than water. Because of its low viscosity, this is the least explosive form of magma. Basaltic magma may found in regions such as Hawaii, known for its shield volcanoes., 
+Basaltic magma forms minerals such as calcium-rich plagioclase feldspar and pyroxene. The water composition of basaltic magma varies dependent on the evolution of the magma chamber. Arc magmas, such as Izarú in Costa Rica, range from 3.2-3.5 wt.%.
+
+
+=== Andesitic magma ===
+Andesitic magma is an intermediate magma and is approximately evenly dispersed regarding iron, magnesium, calcium, sodium, and potassium. The silica composition of andesitic magma ranges from 55 - 65 wt.%. It forms in temperatures ranging from approximately 1470 °F to 1830 °F.,  Andesitic magma has an intermediate viscosity and volatiles content. It forms minerals such as plagioclase feldspar, mica, and amphibole.
+
+
+=== Rhyolitic magma ===
+Rhyolitic magma is felsic and the most abundant in silica, potassium, and sodium but the lowest in iron, magnesium, and calcium. The silica composition of rhyolitic magma ranges from 65-75 wt.%. It forms in the lowest temperature range, from about 1200 °F to 1470 °F.,  Rhyolitic magma has the highest viscosity and gas content. It produces the most explosive volcanic eruptions, including the catastrophic eruption of Mount Vesuvius. It forms minerals such as orthoclase feldspar, sodium-rich plagioclase feldspar, quartz, mica, and amphibole.
+
+
+== Water in silicate melts ==
+Precipitation of minerals is affected by water solubility within silicate melts, which typically exists as hydroxyl groups bound to Si4+ or Group 1 and Group 2 cations in concentrations ranging from approximately 6-7 wt. %., Specifically, the equilibrium of water and dissolved oxygen yields hydroxides, where the Keq has been approximated between 0.1 and 0.3.
+This inherent solubility is low yet varies greatly depending on the pressure of the system. Rhyolitic magmas have the highest solubility, ranging from approximately 0% at the surface to nearly 10% at 1100 °C and 5 kbar. Degassing occurs when hydrous magma is uplifted, gradually converting the dissolved water to aqueous phase. This aqueous phase is typically abundant in volatiles, metals (copper, lead, zinc, silver and gold), and Group 1 and Group 2 cations. Dependent on which cation the hydroxyl is bound to, it significantly impacts the properties of a volcanic eruption, particularly its explosiveness. During unusually high temperature and pressure conditions exceeding 374 °C and 218 bar, water enters a supercritical fluid state and becomes no longer a liquid or a gas.
+
+
+== Stable isotope data ==
+Isotopic data from various locations within the Mid-Atlantic Ridge indicates the presence of mafic-to-felsic intrusive igneous rocks, including gabbro, diorite, and plagiogranite. These rocks showed high-grade metamorphism because of the presence of magmatic water, exceeding 600 °C. This deformation depleted host rocks of 18O, leading to further analysis of the ratio of 18O to 16O (δ18O).
+Water in equilibrium with igneous melts should bear the same isotopic signature for 18O and δ2H. However, isotopic studies of magmatic water have demonstrated similarities to meteoric water, indicating circulation of magmatic and meteoric groundwater systems.
+Isotopic analyses of fluid inclusions indicate a wide range of δ18O and δ2H content. Studies within these environments have shown an abundance of 18O and depletion in 2H relative to SMOW and meteoric waters. Within ore deposits, fluid inclusion data showed that the presence of δ18O vs δ2H are within the expected range.
+
+
+== See also ==
+Connate fluids
+
+
+== References ==

data/en.wikipedia.org/wiki/Origin_of_water_on_Earth-0.md

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+---
+title: "Origin of water on Earth"
+chunk: 1/4
+source: "https://en.wikipedia.org/wiki/Origin_of_water_on_Earth"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:05.225138+00:00"
+instance: "kb-cron"
+---
+
+The origin of water on Earth is the subject of a body of research in the fields of planetary science, astronomy, and astrobiology. Earth is unique among known planets in having oceans of liquid water on its surface. Liquid water, which is necessary for all known forms of life, continues to exist on the surface of Earth because the planet is at a far enough distance (known as the habitable zone) from the Sun that it does not lose its water, but not so far that low temperatures cause all water on the planet to freeze.
+It was long thought that Earth's water did not originate from the planet's region of the protoplanetary disk. Instead, it was hypothesized water and other volatiles must have been delivered to Earth from the outer Solar System later in its history. Recent research, however, indicates that hydrogen inside the Earth played a role in the formation of the ocean. The two ideas are not mutually exclusive, as there is also evidence that water was delivered to Earth by impacts from icy planetesimals similar in composition to asteroids in the outer edges of the asteroid belt.
+
+== History of water on Earth ==
+One factor in estimating when water appeared on Earth is that water is continually being lost to space. H2O molecules in the atmosphere are broken up by photolysis, and the resulting free hydrogen atoms can sometimes escape Earth's gravitational pull. When the Earth was younger and less massive, water would have been lost to space more easily. Lighter elements like hydrogen and helium are expected to leak from the atmosphere continually, but isotopic ratios of heavier noble gases in the modern atmosphere suggest that even the heavier elements in the early atmosphere were subject to significant losses. In particular, xenon is useful for calculations of water loss over time. Not only is it a noble gas (and therefore is not removed from the atmosphere through chemical reactions with other elements), but comparisons between the abundances of its nine stable isotopes in the modern atmosphere reveal that the Earth lost at least one ocean of water, a volume of water approximately equal to modern ocean volume, early in its history. This is likely to have occurred between the Hadean and Archean eons in cataclysmic events such as the moon forming impact.
+Any water on Earth during the latter part of its accretion would have been disrupted by the Moon-forming impact (~4.5 billion years ago), which likely vaporized much of Earth's crust and upper mantle and created a rock-vapor atmosphere around the young planet. The rock vapor would have condensed within two thousand years, leaving behind hot volatiles which probably resulted in a majority carbon dioxide atmosphere with hydrogen and water vapor. Afterward, liquid water oceans may have existed despite the surface temperature of 230 °C (446 °F) due to the increased atmospheric pressure of the CO2 atmosphere. As the cooling continued, most CO2 was removed from the atmosphere by subduction and dissolution in ocean water, but levels oscillated wildly as new surface and mantle cycles appeared.
+
+Geological evidence also helps constrain the time frame for liquid water existing on Earth. A sample of pillow basalt (a type of rock formed during an underwater eruption) was recovered from the Isua Greenstone Belt and provides evidence that water existed on Earth 3.8 billion years ago. In the Nuvvuagittuq Greenstone Belt, Quebec, Canada, rocks dated at 3.8 billion years old by one study and 4.28 billion years old by another show evidence of the presence of water at these ages. If oceans existed earlier than this, any geological evidence has yet to be discovered (which may be because such potential evidence has been destroyed by geological processes like crustal recycling). More recently, in August 2020, researchers reported that sufficient water to fill the oceans may have always been on the Earth since the beginning of the planet's formation.
+Unlike rocks, minerals called zircons are highly resistant to weathering and geological processes and so are used to understand conditions on the very early Earth. Mineralogical evidence from zircons has shown that liquid water and an atmosphere must have existed 4.404 ± 0.008 billion years ago, very soon after the formation of Earth. This presents somewhat of a paradox, as the cool early Earth hypothesis suggests temperatures were cold enough to freeze water between about 4.4 billion and 4.0 billion years ago. Other studies of zircons found in Australian Hadean rock point to the existence of plate tectonics as early as 4 billion years ago. If true, that implies that rather than a hot, molten surface and an atmosphere full of carbon dioxide, early Earth's surface was much as it is today (in terms of thermal insulation). The action of plate tectonics traps vast amounts of CO2, thereby reducing greenhouse effects, leading to a much lower surface temperature and the formation of solid rock and liquid water.
+
+== Earth's water inventory ==

data/en.wikipedia.org/wiki/Origin_of_water_on_Earth-1.md

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+---
+title: "Origin of water on Earth"
+chunk: 2/4
+source: "https://en.wikipedia.org/wiki/Origin_of_water_on_Earth"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:05.225138+00:00"
+instance: "kb-cron"
+---
+
+While the majority of Earth's surface is covered by oceans, those oceans make up just a small fraction of the mass of the planet. The mass of Earth's oceans is estimated to be 1.37 × 1021 kg, which is 0.023% of the total mass of Earth, 6.0 × 1024 kg. An additional 5.0 × 1020 kg of water is estimated to exist in ice, lakes, rivers, groundwater, and atmospheric water vapor. A significant amount of water is also stored in Earth's crust, mantle, and core. Unlike molecular H2O that is found on the surface, water in the interior exists primarily in hydrated minerals or as trace amounts of hydrogen bonded to oxygen atoms in anhydrous minerals. Hydrated silicates on the surface transport water into the mantle at convergent plate boundaries, where oceanic crust is subducted underneath continental crust. While it is difficult to estimate the total water content of the mantle due to limited samples, approximately three times the mass of the Earth's oceans could be stored there. Similarly, the Earth's core could contain four to five oceans' worth of hydrogen.
+While not considered to be one of the major sources of water on the planet, it should also be noted that biological processes such as photosynthesis and respiration are key factors in the hydrologic cycling of water on earth. These processes may have also had a more vital role on the early earth, and as such, they could impact the amount of available water present in a given location at a given time. This is due to one of these aforementioned processes consuming water, and the other generating water, and the balance between them is therefore what truly determines their impact. If photosynthesis occurs in higher degrees than respiration, earth's water inventory would decrease, while if respiration occurs in higher degrees than photosynthesis, earth's water inventory would increase. 
+
+== Hypotheses for the origins of Earth's water ==
+
+=== Within Earth itself ===
+Miozzi, et al., (2025) propose that a hydrogen-infused magma ocean  could have presented on Earth itself at ambient temperatures over 4000 K. The experiments of Miozzi, et al., (2025) find that copious amounts of hydrogen can dissolve into a magma melt at 4000 K, with a lesser dependence on pressures, from 16 to 60 GPa. Further, the reduction of iron oxide by hydrogen leads to the production of significant amounts of water, along with the formation of iron blebs.  
+
+=== Extraplanetary sources ===
+Water has a much lower condensation temperature than other materials that compose the terrestrial planets in the Solar System, such as iron and silicates. The region of the protoplanetary disk closest to the Sun was very hot early in the history of the Solar System, with temperatures ranging from 500-1500 Kelvin or 200-1200 Celsius, and therefore, it is not feasible that oceans of water condensed with the Earth as it formed. Further from the young Sun where temperatures were lower, water could condense and form icy planetesimals, which accumulated to form the Oort cloud. The boundary of the region where ice could form in the early Solar System is known as the frost line (or snow line), and is located in the modern asteroid belt, between about 2.7 and 3.1 astronomical units (AU) from the Sun. It is therefore necessary that objects forming beyond the frost line–such as comets, trans-Neptunian objects, and water-rich meteoroids (protoplanets)–delivered water to Earth. However, the timing of this delivery is still in question.
+One hypothesis claims that Earth accreted (gradually grew by accumulation of) icy planetesimals about 4.5 billion years ago, when it was 60 to 90% of its current size. In this scenario, Earth was able to retain water in some form throughout accretion and major impact events. This hypothesis is supported by similarities in the abundance and the isotope ratios of water between the oldest known carbonaceous chondrite meteorites and meteorites from Vesta, both of which originate from the Solar System's asteroid belt. It is also supported by studies of osmium isotope ratios, which suggest that a sizeable quantity of water was contained in the material that Earth accreted early on. Measurements of the chemical composition of lunar samples collected by the Apollo 15 and 17 missions further support this, and indicate that water was already present on Earth before the Moon was formed.

data/en.wikipedia.org/wiki/Origin_of_water_on_Earth-2.md

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+---
+title: "Origin of water on Earth"
+chunk: 3/4
+source: "https://en.wikipedia.org/wiki/Origin_of_water_on_Earth"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:05.225138+00:00"
+instance: "kb-cron"
+---
+
+One problem with this hypothesis is that the noble gas isotope ratios of Earth's atmosphere are different from those of its mantle, which suggests they were formed from different sources. To explain this observation, a so-called "late veneer" theory has been proposed in which water was delivered much later in Earth's history, after the Moon-forming impact. However, the current understanding of Earth's formation allows for less than 1% of Earth's material accreting after the Moon formed, implying that the material accreted later must have been very water-rich. Models of early Solar System dynamics have shown that icy asteroids could have been delivered to the inner Solar System (including Earth) during this period if Jupiter migrated closer to the Sun. Jupiter's relatively quick development, however, made it difficult for the inner solar system to receive matter from the outer solar system, limiting the accumulation of water on the terrestrial planets. This is in addition to other factors, such as the conditions for the goldilocks zone, where liquid water, and by extension life as we know it, can exist, as opposed to solid ice forming snowball planets or gaseous water vapor forming gas giants.
+Yet a third hypothesis, supported by evidence from molybdenum isotope ratios from a 2019 study, suggests that the Earth gained most of its water from the same interplanetary collision that caused the formation of the Moon. Albeit, as mentioned above, the majority of this water would have remained in a gaseous phase until significant planetary cooling occurred. 
+The evidence from 2019 shows that the molybdenum isotopic composition of the Earth's mantle originates from the outer Solar System, likely having brought water to Earth. The explanation is that Theia, the planet said in the giant-impact hypothesis to have collided with Earth 4.5 billion years ago forming the Moon, may have originated in the outer Solar System rather than in the inner Solar System, bringing water and carbon-based materials with it.
+
+== Geochemical analysis of water in the Solar System ==
+
+Isotopic ratios provide a unique "chemical fingerprint" that is used to compare Earth's water with reservoirs elsewhere in the Solar System. One such isotopic ratio, that of deuterium to hydrogen (D/H), is particularly useful in the search for the origin of water on Earth. Hydrogen is the most abundant element in the universe, and its heavier isotope deuterium can sometimes take the place of a hydrogen atom in molecules like H2O. Most deuterium was created in the Big Bang or in supernovae, so its uneven distribution throughout the protosolar nebula was effectively "locked in" early in the formation of the Solar System. By studying the different isotopic ratios of Earth and of other icy bodies in the Solar System, the likely origins of Earth's water can be researched.
+
+=== Earth ===
+The deuterium to hydrogen ratio for ocean water on Earth is known very precisely to be (1.5576 ± 0.0005) × 10−4. This value represents a mixture of all of the sources that contributed to Earth's reservoirs, and is used to identify the source or sources of Earth's water. The ratio of deuterium to hydrogen has increased over the Earth's lifetime between 2 and 9 times the ratio at the Earth's origin, because the lighter isotope is more likely to leak into space in atmospheric loss processes. Hydrogen beneath the Earth's crust is thought to have a D/H ratio more representative of the original D/H ratio upon formation of the Earth, because it is less affected by those processes. Analysis of subsurface hydrogen contained in recently released lava has been estimated to show that there was a 218‰ higher D/H ratio in the primordial Earth compared to the current ratio. No process is known that can decrease Earth's D/H ratio over time. This loss of the lighter isotope is one explanation for why Venus has such a high D/H ratio, as that planet's water was vaporized during the runaway greenhouse effect and subsequently lost much of its hydrogen to space.
+
+=== Asteroids ===
+
+Multiple geochemical studies have concluded that asteroids are most likely the primary source of Earth's water. Carbonaceous chondrites—which are a subclass of the oldest meteorites in the Solar System—have isotopic levels most similar to ocean water. The CI and CM subclasses of carbonaceous chondrites specifically have hydrogen and nitrogen isotope levels that closely match Earth's seawater, which suggests water in these meteorites could be the source of Earth's oceans. Two 4.5 billion-year-old meteorites found on Earth that contained liquid water alongside a wide diversity of deuterium-poor organic compounds further support this. Earth's current deuterium to hydrogen ratio also matches ancient eucrite chondrites, which originate from the asteroid Vesta in the outer asteroid belt. CI, CM, and eucrite chondrites are believed to have the same water content and isotope ratios as ancient icy protoplanets from the outer asteroid belt that later delivered water to Earth.
+A further asteroid particle study supported the theory that a large source of earth's water has come from hydrogen atoms carried on particles in the solar wind which combine with oxygen on asteroids and then arrive on earth in space dust. Using atom probe tomography the study found hydroxide and water molecules on the surface of a single grain from particles retrieved from the asteroid 25143 Itokawa by the Japanese space probe Hayabusa.

data/en.wikipedia.org/wiki/Origin_of_water_on_Earth-3.md

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+---
+title: "Origin of water on Earth"
+chunk: 4/4
+source: "https://en.wikipedia.org/wiki/Origin_of_water_on_Earth"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:05.225138+00:00"
+instance: "kb-cron"
+---
+
+=== Comets ===
+Comets are kilometer-sized bodies made of dust and ice that originate from the Kuiper belt (20-50 AU) and the Oort cloud (>5,000 AU), but have highly elliptical orbits which bring them into the inner solar system. Their icy composition and trajectories which bring them into the inner solar system make them a target for remote and in situ measurements of D/H ratios.
+It is implausible that Earth's water originated only from comets, since isotope measurements of the deuterium to hydrogen (D/H) ratio in comets Halley, Hyakutake, Hale–Bopp, 2002T7, and Tuttle, yield values approximately twice that of oceanic water. This is also supported by analysis using the comparison of isotopic ratios for both carbon and nitrogen isotopes, which attribute only a few percent of the water present on earth to comet sources, indicating a much higher reliance on incoming asteroid matter. Using the cometary D/H ratio, models predict that less than 10% of Earth's water was supplied from comets.
+Other, shorter period comets (<20 years) called Jupiter family comets likely originate from the Kuiper belt, but have had their orbital paths influenced by gravitational interactions with Jupiter or Neptune. 67P/Churyumov–Gerasimenko is one such comet that was the subject of isotopic measurements by the Rosetta spacecraft, which found the comet has a D/H ratio three times that of Earth's seawater. Another Jupiter family comet, 103P/Hartley 2, has a D/H ratio which is consistent with Earth's seawater, but its nitrogen isotope levels do not match Earth's.
+
+== See also ==
+Water on terrestrial planets of the Solar System
+
+== Notes ==
+
+== References ==
+
+== External links ==
+Dr. C's Ocean World: "How the Oceans Formed" (archived copy)
+Nature journal: "Earth has water older than the Sun"

data/en.wikipedia.org/wiki/Scientific_school-0.md

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+---
+title: "Scientific school"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Scientific_school"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:06.886937+00:00"
+instance: "kb-cron"
+---
+
+Scientific school (school of scientific traditions) is an established system of scientific views, as well as a scientific community adhering to these views. The formation of a scientific school occurs under the influence of a leader, whose erudition, range of interests, and working style are decisive for attracting new collaborators. Relationships within such a scientific team facilitate the exchange of information at the level of ideas (rather than final research results), which significantly increases the efficiency of creative scientific work.
+
+
+== History ==
+
+At the stage of protoscience, the schools that existed at that time could act as independent centers or institutes. Later, scientific schools came to be understood as real informal collectives of scientists.
+In antiquity, schools of arts and philosophical thought arose, such as the Aristotelian Peripatetics.
+In the Middle Ages, the printing press created an important technical prerequisite for the emergence of schools of thought spanning several geographical centers. This facilitated the process of learning and disseminating the ideas of different schools. Each of them acquired a propaganda tool - periodically published collections, journals, bulletins, and other scientific periodicals. Its own printed organ is a significant feature of a school of scientific thought. It is reflected in the history of science and facilitates the search for scientific results of its activities.
+Michael Polanyi is considered one of the founders of Western sociology of knowledge, having explored the problems of scientific traditions, scientific schools, and issues of intrascientific communication.
+Modern scientific schools are often universities. Their structural units, departments, are analogues of creative workshops, and the scientists heading them (usually professors) are the masters themselves, the "first persons" of the schools, who often subsequently lend their famous names to them. No less significant in scientific terms, schools arise in different countries around academic research centers and research institutes.
+Distinguished two meanings: 
+
+a hierarchical and self-reproducing scientific community that has made a major contribution to world science;
+a community occupying a certain niche in national science, reproducing itself in new generations of specialists, and distinguished by a certain methodology.
+According to biochemist Garry Abelev, if in the mid-20th century a clear division of scientists into schools was visible, this rather referred to the pre-paradigm period, whereas now, when paradigms have been established,
+
+There are fewer and fewer schools because all our knowledge is becoming more structured. Schools perhaps remain as organizational associations - laboratories, departments where, due to low staff turnover, stable groups of employees are maintained for many years. They develop a certain similarity in views, in criteria, and this, in my opinion, is more like schools. But in general, in my opinion, in immunology and virology, schools are blurring, dissolving in the general structure of knowledge of a given field.
+
+
+== Characteristics ==
+A school implies the presence of a scientific leader (a teacher or an idea, after his death) and followers (students).
+Scientific schools become centers of the most intensive concentration of creative energy, most actively influencing scientific progress.
+Schools are a symptom of the immaturity of a science. With the establishment of a paradigm and the transition to "normal" science, schools leave the stage. A commonality of theoretical and methodological positions of all representatives of a given science is established.
+The issue of the life cycles of scientific schools is the least developed in the scientific literature. Sometimes they cease to exist simply due to lack of funding. However, when determining leading schools, their life cycle is often not taken into account, so often renowned but stagnant schools receive support, rather than emerging and highly promising scientific schools.
+The degeneration of scientific schools (their decline) occurs in two main forms: bureaucratization and commercialization. Both of these forms are associated with the modernization and modification of existing results, and boil down to project management instead of scientific search, which kills creativity, and consequently the scientific school itself.
+
+
+== Official status ==
+
+Since 1995 to the present, in Russia, the status of "Leading Scientific School of the Russian Federation" is awarded to scientific teams (which have gained fame for their high level of research in a recognized and sufficiently broad scientific direction, stability of traditions, continuity of generations in the training of highly qualified scientific personnel) based on the results of a competitive selection by the Council for Grants of the President of the Russian Federation and the Russian Ministry of Education and Science.
+In some countries, for example, Finland and Norway, a close analogue is the status of Center of Excellence (CoE).
+
+
+== See also ==
+School (in science and art); School (disambiguation); Science school
+Science studies
+Cognition
+Scientific method
+Center of excellence
+
+
+== References ==
+
+
+== Literature ==
+Polanyi M. Personal Knowledge. The University of Chicago Press, Chicago, 1962 (First published 1958)
+Polanyi M. The Tacit Dimension. New York: Doubleday & Company, inc. Garden city, 1966. 108 p.
+Gruzevich D. Yu. Scientific School as a Form of Activity // Questions of the History of Natural Science and Technology. 2003. No. 1. P. 64–93.
+Rapatsevich E. S. Pedagogy // Large Modern Encyclopedia. Minsk: Sovremennoe Slovo, 2005. P. 667–668.
+Onoprienko V. I. Scientific School as a Sociological Phenomenon // Bulletin of the National Aviation University. Philosophy. Culturology. 2009. Issue 2. P. 33–37.
+Onoprienko V. I. Scientific Schools: Science Studies Context // Science and Science of Science. 2009. No. 4. P. 123–126.
+Onoprienko V. I. Scientific Schools: Problems of Traditions and Innovations // Almanac of Theory and History of Historical Science. Issue 4. Kyiv: IIU. NASU, 2009. P. 138–152.
+Krivotruchenko V. K. Scientific Schools // Znanie. Ponimanie. Umenie|Knowledge. Understanding. Skill. 2011. No. 2 (March — April).
+Ustyuzhanina E. V., Evsyukov S. G., Petrov A. G. et al. Scientific School as a Structural Unit of Scientific Activity. Moscow: Central Economics and Mathematics Institute RAS, 2011. 73 p.
+Schools in Science. Moscow: Nauka, 1977. 523 p. (Science of Science: Problems and Research)
+Vtorov I. P. Dokuchaev school of soil science: Origins and Development // 21st Annual Conference of the IIET RAS. Vol. 2. Moscow: LENAND, 2015. P. 241–245.
+Vtorov I. P., Babenko A. B., Bokova A. I., Davydova Yu. Yu., Potapov M. B. Uvarov A. V., Kuznetsova N. A. The History of N. M. Chernova’s Scientific School of Soil Zoology at the Moscow Pedagogical State University // Chinese Annals of History of Science and Technology. 2025. Vol. 9. No. 2. Pp. 133—160.
+
+
+== Links ==
+
+Kupershtokh N. A. Scientific Schools of Russia and Siberia: Problems of Study. Scientific Schools in the Siberian Branch of the RAS.
+Bibliography on Problems of Scientific Schools. Novosibirsk Scientific Center.

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+---
+title: "Sheffield Scientific School"
+chunk: 1/2
+source: "https://en.wikipedia.org/wiki/Sheffield_Scientific_School"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:10.717906+00:00"
+instance: "kb-cron"
+---
+
+Sheffield Scientific School was founded in 1847 as a school of Yale College in New Haven, Connecticut, for instruction in science and engineering. Originally named the Yale Scientific School, it was renamed in 1861 in honor of Joseph E. Sheffield, a railroad executive. The school was incorporated in 1871. The Sheffield Scientific School helped establish a model of American higher education which incorporated both the sciences and the liberal arts. Following World War I, its curriculum gradually became completely integrated with Yale College. "The Sheff" ceased to function as a separate entity in 1956.
+
+== History ==
+
+After technological developments in the early nineteenth century, such as the electric telegraph, an interest was fostered in teaching applied science at universities. Harvard established the Lawrence Scientific School in 1846 and Dartmouth began the Chandler Scientific School in 1852. The stage was set at Yale for the transition in education beginning in 1846, when professorships of agricultural chemistry (John Pitkin Norton) and practical chemistry (Benjamin Silliman Jr.) were established. In 1847, the School of Applied Chemistry became part of a newly created Department of Philosophy and the Arts (later, the Yale Graduate School). Classes and labs were hosted in the Second President's House on Yale's Old Campus until funding and a suitable facility could be found.
+Norton died in 1852 and was followed by John Addison Porter. The professorship for applied chemistry was followed in 1852 by one for civil engineering, (William Augustus Norton) establishing a school of engineering. These programs made up the Yale Scientific School.
+
+In 1853 and 1854, science and engineering courses were listed in the Yale College course catalog as offered by the Yale Scientific School. Porter elicited help from his father-in-law, Joseph Earl Sheffield (1793-1882), and in 1858, Sheffield donated over US$100,000 to purchase the old Medical Department building for the scientific school. This gift included two newly-renovated wings within the building. The old Yale Medical School building on the northeast corner of Grove and Prospect Streets was renovated and renamed (South) Sheffield Hall. (It was demolished in 1931 and was on the current site of Sterling Tower, Sheffield Hall and Strathcona Hall (SSS).) Sheffield's building reinforced the division of Hillhouse Avenue into an upper, residential section, and a lower section devoted to education. In 1861, the school became the Sheffield Scientific School.
+Sheffield was one of Yale's greatest benefactors and continued to support the school throughout his life, giving a total of about US$500,000. Yale also received US$591,000 from his will as well as his house, the Sheffield mansion, designed and originally owned by Ithiel Town (demolished in 1957). The school also benefited from the Morrill Act starting in 1863 and an agricultural course was begun. Land grant status, however, was transferred to the Storrs Agricultural School in 1893 after arguments by the state grange that the school was not a proper "farm school".
+
+== Education and student life ==
+The Sheffield School innovated with an undergraduate course offering science and mathematics as well as economics, English, geography, history, modern languages, philology and political science. Sheffield also pioneered graduate education in the United States, granting the first Ph.D. in the United States in 1861 as well as the first engineering Ph.D. to Josiah Willard Gibbs in 1863, and the first geology Ph.D. to William North Rice in 1867.
+Unlike Yale College students at the time, Sheffield students had "no dorms, no required chapel, no disciplinary marks and no proctors". The Academical Department of Yale (Ac) and Sheffield (Sheff) became rivals. Loomis Havemeyer, alumnus and registrar at Sheffield, stated: "During the second half of the nineteenth century Yale College and Sheffield Scientific School, separated by only a few streets, were two separate countries on the same planet." The Ac students studied liberal arts and would look down on the practical Sheff students.
+Sheffield had its own student secret societies, including the Colony Club, 1848 (now Berzelius), the Cloister, 1863 (now Book and Snake), St. Anthony Hall, 1867 (now a 3-year society, also called Delta Psi), St. Elmo, 1889 (also a senior society), as well as Franklin Hall, 1865 (Theta Xi), York Hall, 1877 (Chi Phi), Sachem Hall, 1893 (Phi Sigma Kappa), and Vernon Hall, 1908 (now Myth and Sword). The Yale Scientific magazine was founded at Sheffield in 1894, the first student magazine devoted to the sciences.
+
+== Other buildings ==
+In 1872–73, Sheffield Scientific School's first new building, North Sheffield Hall was built, designed by Josiah Cleaveland Cady, on what had been the gardens of the Town-Sheffield mansion. This was followed by Winchester Hall (1892) and Sheffield Chemical (1894-5, J. Cleaveland Cady). Of these, only the latter, Sheffield Chemical, is still standing, renovated and renamed Arthur K. Watson Hall. Becton Laboratory (designed by Marcel Breuer, 1970) now stands on the site of North Sheffield and Winchester Halls (demolished in 1967). Further expansion brought Kirtland Hall (1902, Kirtland Cutter), Hammond Laboratory (1904, W. Gedney Beatty), Leet Oliver Hall (1908, Charles C. Haight), Mason Laboratory (1911, Charles C. Haight) and Dunham Laboratory (1912, Henry Morse; addition 1958, Douglas Orr), all still standing except Hammond which was razed in 2009 to make way for two new residential colleges.
+
+== Reorganization ==

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+---
+title: "Sheffield Scientific School"
+chunk: 2/2
+source: "https://en.wikipedia.org/wiki/Sheffield_Scientific_School"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T03:51:10.717906+00:00"
+instance: "kb-cron"
+---
+
+During the 1918-1919 reorganization of the educational structure of Yale University, the three years "select" course at Sheffield Scientific School was eliminated and a four-year course of study for those studying "professional science" and "engineering" was approved, while graduate courses were transferred to the Graduate School, leaving only undergraduate courses taught at Sheffield Scientific School from 1919 to 1945, coexisting with Yale College's science programs. The centennial was celebrated in 1947 with the Silliman lectures given by Ernest O. Lawrence, Linus Pauling, W. M. Stanley and George Wells Beadle.
+The first degree of Bachelor of Science was awarded in 1922 to the graduating class of the Sheffield Scientific School. In 1932, the School of Engineering was reestablished and Sheffield Scientific School engineering classes were transferred to the new school. In 1945, the Sheffield Scientific School resumed its original function of graduate level instruction in science. Undergraduate courses for the Bachelor of Science degree were transferred to Yale College, and undergraduate courses for a Bachelor of Science in industrial administration were transferred to the School of Engineering.
+This transition occurred gradually, through the influence of "aggressive, powerful alumni" (including Edwin Oviatt, editor of the Yale Alumni Weekly) who "took control out of President Hadley's hands and forced a radical reorganization of Yale". In 1956, the Sheffield Scientific School was terminated as an active school. The Board of Trustees still exists to oversee the Sheffield Scientific School property and meet legal requirements. The school's faculty is defined as teachers of science to graduate students under the Division of Science. Engineering teaching and research is now conducted within the School of Engineering & Applied Science.
+
+== Directors ==
+George Jarvis Brush (Professor of Mineralogy) from 1872 to 1898.
+Russell Henry Chittenden (Professor of Physiological Chemistry) from 1898 to 1922.
+Charles Hyde Warren (Sterling Professor of Geology) from 1922 to 1945.
+Edmund Ware Sinnott (Sterling Professor of Botany) from 1945 to 1956.
+
+== Notable faculty ==
+Charles Emerson Beecher, paleontologist, member of the governing board
+William Henry Brewer, botanist, first chair of agriculture, as well as a graduate from the first class of the school
+Daniel Cady Eaton, botanist
+Daniel Coit Gilman, geographer, helped plan and raise funds
+Richard F. Humphreys (1911–1968), physicist and author, president of Cooper Union
+Thomas Lounsbury, American literary historian, professor of English and librarian at Sheff
+Chester S. Lyman (1814–1890), industrial mechanics; inventor of surveying and astronomical instruments
+William Crosby Marshall (1870-1934), Mechanical engineer, Professor of Machine Design and Descriptive Geometry and author.
+Lafayette Mendel, biochemist
+Mansfield Merriman (1848–1925), civil engineering; author of "A Treatise on Hydraulics and on the Strength of Materials", 1877
+John Pitkin Norton, chemist, faculty member of Yale's department of education in applied science, which gave rise to Sheffield Scientific School.
+William Augustus Norton, civil engineer, founding faculty member
+John Addison Porter, chemist
+Charles Brinckerhoff Richards, engineer chair of Mechanical Engineering from 1884–1909
+Benjamin Silliman Jr., chemist, founding faculty member
+William Petit Trowbridge (1828–1892), mechanical engineering; published the first cantilever bridge design; Member, National Academy of Science
+Addison Emery Verrill, zoologist and geologist
+Francis Amasa Walker, economist, third president of the Massachusetts Institute of Technology
+William Dwight Whitney, organized and taught in the department of modern languages; member of the governing board
+
+== Notable alumni ==
+Joseph Wright Alsop IV (1876–1953), politician and insurance executive; father of Joseph Alsop
+Wilbur Olin Atwater (1844–1907), chemist known for his studies of human nutrition and metabolism
+Clifford W. Beers, mental health pioneer
+Jules Blankfein, Class of 1921, physician & financier; founder, Physicians' Hospital, New York; uncle of Lloyd Blankfein
+William Edward Boeing, aviator
+John Vernou Bouvier III, stockbroker and socialite; father of Jackie Kennedy, First Lady
+Chester Bowles, American politician
+Bradford Brinton, engineer; collector of fine Western art, which eventually resulted in the primary collection of The Brinton Museum
+J. Twing Brooks, U. S. congressman
+Malcolm Greene Chace (1875–1955), class of 1896. One of the founders of the Yale hockey team, American financier, textile industrialist, and tennis champion
+Henry Boardman Conover, ornithologist
+Arthur Louis Day, geophysicist and volcanologist
+Franklin M. Doolittle (1893–1979), Class of 1915, radio pioneer
+Charles Benjamin Dudley, chemist
+Isadore Dyer, physician
+Lee de Forest, electronics inventor
+Francis I. du Pont, chemist
+Pete Falsey, Major League baseball player
+Joseph W. Frazer, automobile magnate
+James Terry Gardiner, surveyor and engineer
+Josiah Willard Gibbs, mathematical physicist and physical chemist
+T. Keith Glennan, first NASA administrator
+Harold L. Green, chain store founder
+John Campbell Greenway, American mining and steel executive, General, U.S. Army
+Harry Frank Guggenheim, businessman, philanthropist
+John Hays Hammond, mining engineer, philanthropist, faculty member. He endowed a program at Sheff in mining and metallurgy and accepted a professorship. He contributed $100,000 for the construction of Hammond Laboratory, which is named for him.
+John Hays Hammond Jr., inventor, “father of radio control’’
+John Bell Hatcher, paleontologist
+Daniel Webster Hering, physicist
+Robert J. Huber, Michigan politician, businessman
+Tony Hulman (1924) businessman, owner of Indianapolis Motor Speedway 1945–1977
+Edward Hopkins Jenkins (1850–1931), agricultural chemist; director of the Connecticut Agricultural Experiment Station (1900–1923)
+Treat Baldwin Johnson, chemist
+Clarence King, American geologist and mountaineer
+Charles N. Lowrie, American landscape architect
+Duane Lyman, architect
+Othniel Charles Marsh, paleontologist
+Champion Mathewson, metallurgist
+Truman Handy Newberry, American businessman and politician
+Frederick E. Olmsted, forester
+Thomas Wharton Phillips Jr., U. S. Congressman
+William S. Reyburn, U.S. Congressman
+William North Rice, geologist and theologian
+Stanley Pickett Rockwell (1907), metallurgist and co-inventor of the Rockwell hardness test
+Pierce Schenck (1878–1930), business executive from Dayton, Ohio
+William Thompson Sedgwick, bacteriologist and public health scientist
+George B. Selden, lawyer and inventor
+Sidney Irving Smith, zoologist
+James Graham Phelps Stokes, philanthropist, publicist, and political activist
+Zhan Tianyou, Chinese railroad engineer, "father of China's railroad"
+Juan Trippe, founder and CEO of Pan American World Airways
+Yamakawa Kenjirō, Japanese samurai of Aizu Domain, member of Byakkotai, physicist, member of the House of Peers
+Thomas Yawkey, owner of the Boston Red Sox for 44 years
+
+== See also ==
+Austin Cornelius Dunham - major early donor
+
+== References ==
+
+== Further reading ==
+Cunningham, W. Jack, Engineering at Yale, Connecticut Academy of Arts and Sciences, New Haven, Connecticut, 1992. ISBN 1-878508-06-7
+Pinnell, Patrick L., Yale University: The Campus Guide, Princeton Architectural Press, New York, 1999.
+Shimp, Andy, Sheffield Scientific School.
+Chittenden, Russell H., History of the Sheffield Scientific School of Yale University, 1846–1922. New Haven, Conn.: Yale University Press, 1928.
+Furniss, Edgar S., The Graduate School of Yale: A Brief History. New Haven, Conn.: Purington Rollins, 1965.
+Veysey, Laurence R., The Emergence of the American University. Chicago: University of Chicago Press, 1965.
+Warren, Charles H. The Sheffield Scientific School from 1847 to 1947. In The Centennial of the Sheffield Scientific School. Edited by George Alfred Baitsell. New Haven, Conn.: Yale University Press, 1950.
+
+== External links ==
+
+Yale Engineering through the Centuries