3.5 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Carl Sagan | 5/13 | https://en.wikipedia.org/wiki/Carl_Sagan | reference | science, encyclopedia | 2026-05-05T13:17:36.414677+00:00 | kb-cron |
Former student David Morrison described Sagan as "an 'idea person' and a master of intuitive physical arguments and 'back of the envelope' calculations", and Gerard Kuiper said that "Some persons work best in specializing on a major program in the laboratory; others are best in liaison between sciences. Dr. Sagan belongs in the latter group." Sagan's contributions were central to the discovery of the high surface temperatures of the planet Venus. In the early 1960s no one knew for certain the basic conditions of Venus' surface, and Sagan listed the possibilities in a report later depicted for popularization in a Time Life book Planets. His own view was that Venus was dry and very hot as opposed to the balmy paradise others had imagined. He had investigated radio waves from Venus and concluded that there was a surface temperature of 500 °C (900 °F). As a visiting scientist to NASA's Jet Propulsion Laboratory, he contributed to the first Mariner missions to Venus, working on the design and management of the project. Mariner 2 confirmed his conclusions on the surface conditions of Venus in 1962. Sagan was among the first to hypothesize that Saturn's moon Titan might possess oceans of liquid compounds on its surface and that Jupiter's moon Europa might possess subsurface oceans of water. This would make Europa potentially habitable. Europa's subsurface ocean of water was later indirectly confirmed by the spacecraft Galileo. The mystery of Titan's reddish haze was also solved with Sagan's help. The reddish haze was revealed to be due to complex organic molecules constantly raining down onto Titan's surface. Sagan further contributed insights regarding the atmospheres of Venus and Jupiter, as well as seasonal changes on Mars. He also perceived climate change as a growing, man-made danger and likened it to the natural development of Venus into a hot, life-hostile planet through a kind of runaway greenhouse effect. He testified to the US Congress in 1985 that the greenhouse effect would change the Earth's climate system. Sagan and his Cornell colleague Edwin Ernest Salpeter speculated about life in Jupiter's clouds, given the planet's dense atmospheric composition rich in organic molecules. He studied the observed color variations on Mars' surface and concluded that they were not seasonal or vegetational changes as most believed, but shifts in surface dust caused by windstorms. He argued in favor of the hypothesis, which has since been accepted, that the high surface temperatures of Venus are the result of the greenhouse effect. Sagan is also known for his research on the possibilities of extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation. As of 2017, Sagan is the most cited SETI scientist and one of the most cited planetary scientists. He edited Icarus from 1975 to 1979. In 1980, he cofounded the Planetary Society.
=== Science popularization ===
Sagan wrote the Encyclopædia Britannica entry on Life, later updated by his first wife, the biologist Lynn Margulis. Sagan's first popular science book was The Cosmic Connection. He introduced the Cosmic Calendar in The Dragons of Eden, which won the 1978 Pulitzer Prize for General Nonfiction. He delivered the 1977 Royal Institution Christmas Lectures on The Planets.