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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Biosignature | 6/6 | https://en.wikipedia.org/wiki/Biosignature | reference | science, encyclopedia | 2026-05-05T13:15:42.723741+00:00 | kb-cron |
Voyager 1 (1979): The first close-up photos of Europa are taken. Scientists propose that a subsurface ocean could cause the tectonic-like marks on the surface. Galileo (1997): The magnetometer aboard this probe detected a subtle change in the magnetic field near Europa. This was later interpreted as a disruption in the expected magnetic field due to the current induction in a conducting layer on Europa. The composition of this conducting layer is consistent with a salty subsurface ocean. Hubble Space Telescope (2012): An image was taken of Europa which showed evidence for a plume of water vapor coming off the surface. The Europa Clipper probe includes instruments to help confirm the existence and composition of a subsurface ocean and thick icy layer. In addition, the instruments will be used to map and study surface features that may indicate tectonic activity due to a subsurface ocean.
===== Dragonfly ===== NASA's Dragonfly lander/aircraft concept is proposed to launch in 2028 and would seek evidence of biosignatures on the organic-rich surface and atmosphere of Titan, as well as study its possible prebiotic primordial soup. Titan is the largest moon of Saturn and is widely believed to have a large subsurface ocean consisting of a salty brine. In addition, scientists believe that Titan may have the conditions necessary to promote prebiotic chemistry, making it a prime candidate for biosignature discovery.
==== Enceladus ====
Although there are no set plans to search for biosignatures on Saturn's sixth-largest moon, Enceladus, the prospects of biosignature discovery there are exciting enough to warrant several mission concepts that may be funded in the future. Similar to Jupiter's moon Europa, there is much evidence for a subsurface ocean to also exist on Enceladus. Plumes of water vapor were first observed in 2005 by the Cassini mission and were later determined to contain salt as well as organic compounds. In 2014, more evidence was presented using gravimetric measurements on Enceladus to conclude that there is in fact a large reservoir of water underneath an icy surface. Mission design concepts include:
Enceladus Life Finder (ELF) Enceladus Life Signatures and Habitability Enceladus Organic Analyzer Enceladus Explorer (En-Ex) Explorer of Enceladus and Titan (E2T) Journey to Enceladus and Titan (JET) Life Investigation For Enceladus (LIFE) Testing the Habitability of Enceladus's Ocean (THEO) All of these concept missions have similar science goals: To assess the habitability of Enceladus and search for biosignatures, in line with the strategic map for exploring the ocean-world Enceladus.
=== Meteorites ===
==== Martian Meteorites ====
===== ALH84001 =====
Microscopic magnetite crystals in the Martian meteorite ALH84001 represent one of the longest-standing and most debated potential biosignatures identified in that specimen. Analyses focused on proposed biominerals, including putative microbial microfossils. These are minute rock-like structures whose morphology was initially suggestive of bacterial shapes. Subsequent studies indicated that these features were likely too small to represent fossilized cells. A broader consensus emerged from these discussions emphasizing that morphological evidence alone is insufficient to substantiate claims of life and must be supported by multiple, independent lines of evidence. Interpretation based solely on morphology are highly subjective and have historically led to numerous misidentifications.
== Search for Life Outside the Solar System == At 4.2 light-years (1.3 parsecs, 40 trillion km, or 25 trillion miles) away from Earth, the closest potentially habitable exoplanet is Proxima Centauri b, which was discovered in 2016. This means it would take more than 18,100 years to get there if a vessel could consistently travel as fast as the Juno spacecraft (250,000 kilometers per hour or 150,000 miles per hour). It is currently not feasible to send humans or even probes to search for biosignatures outside of the Solar System. The only way to search for biosignatures outside of the Solar System is by observing exoplanets with telescopes.
=== Exoplanets ===
==== K2-18b ==== On September 12, 2023, scientists announced that their investigation into exoplanet K2-18b revealed the possible presence of dimethyl sulfide, noting that it is produced only by biotic processes on Earth. In 2025, another paper was published confirming dimethyl sulfide and dimethyl disulfide on the exoplanet. However, a follow-up study questions the James Webb Space Telescope's instrumentation's ability to differentiate the signature of dimethyl sulfide from methane in the data, which is noisy. Additionally, follow-up studies have identified potential abiotic sources.
=== Telescopes === There have been no plausible or confirmed biosignature detections outside of the Solar System. Despite this, it is a rapidly growing field of research due to the prospects of the next generation of telescopes. The James Webb Space Telescope, which launched in December 2021, will be a promising next step in the search for biosignatures. Although its wavelength range and resolution will not be compatible with some of the more important atmospheric biosignature gas bands like oxygen, it will still be able to detect some evidence for oxygen false positive mechanisms. The Habitable Worlds Observatory is a NASA telescope currently in design, expected to launch in the 2040s. It which will specifically target potentially habitable exoplanets, to characterize and observe any potential biosignatures for Earth-like exoplanets. The new generation of ground-based 30-meter class telescopes (Thirty Meter Telescope and Extremely Large Telescope) will have the ability to take high-resolution spectra of exoplanet atmospheres at a variety of wavelengths. These telescopes will be capable of distinguishing some of the more difficult false positive mechanisms such as the abiotic buildup of oxygen via photolysis. In addition, their large collecting area will enable high angular resolution, making direct imaging studies more feasible.
== Bibliography == Gaines, Susan M.; Eglinton, Geoffrey; Rullkotter, Jurgen (2008). Echoes of Life: What Fossil Molecules Reveal about Earth History. Oxford University Press. ISBN 978-0-19-517619-3.
== See also == Bioindicator Taphonomy Technosignature
== References ==