- Person
- Carl Sagan
- Lived
- 1934–1996
- Field
- Astronomy, planetary science
- From
- American
The story
Carl Sagan was trained in both astronomy and biology, and he constantly asked where in the solar system the ingredients for life might be found. In the laboratory he studied how basic chemicals could form the building blocks of life, including experiments showing that radiation could produce amino acids. Two moons of the giant planets especially caught his attention.
He was among the first to propose that Titan, Saturn's largest moon, might have oceans of liquid compounds on its surface. He also helped solve the mystery of Titan's reddish haze, showing that it was made of complex organic molecules constantly raining down onto the surface. With his colleagues W. R. Thompson and B. N. Khare he described Titan as a natural laboratory for the kind of chemistry that may have come before life. In 1983 the Planetary Society, which Sagan led, urged NASA to send a mission to Saturn and Titan.
He also suggested that Europa, one of Jupiter's large moons, might hide an ocean of liquid water beneath its icy crust, which would make it potentially habitable. Sagan was an experimenter on the Galileo mission to Jupiter, and the Galileo spacecraft, which orbited Jupiter from 1995 to 2003, later found indirect evidence for Europa's subsurface ocean.
Both ideas have been richly rewarded. The Cassini-Huygens mission launched in 1997, and in January 2005 its Huygens probe landed on Titan. In 2006 Cassini's radar revealed lakes of liquid hydrocarbons such as methane and ethane near Titan's north pole, the first lakes found anywhere other than Earth. In the 1990s the Planetary Society began campaigning for a Europa mission, which became NASA's Europa Clipper. Launched on October 14, 2024, it is planned to make dozens of close flybys of Europa to study its hidden ocean, alongside Europe's JUICE spacecraft, launched in 2023.
Today Titan and Europa are among the leading targets in the search for life beyond Earth. Sagan's insistence that scientists look for life's chemistry in unexpected places helped put them there.
Why it matters
Sagan's ideas helped turn icy moons into some of the most promising places to look for life elsewhere in the solar system, guiding missions such as Cassini-Huygens and Europa Clipper.
About Carl Sagan
Brooklyn-born astronomer who explained the Venus greenhouse, helped send humanity’s messages on Pioneer and Voyager, and taught Cosmos viewers worldwide to look at the universe with wonder and doubt.
More about Carl Sagan
- Carl Sagan co-founded the Planetary SocietyIn 1980 Carl Sagan co-founded the Planetary Society and became its first president, building a public movement to support the exploration of space.
- Carl Sagan explained why Venus is a furnaceIn the early 1960s Carl Sagan argued from radio data that Venus's surface was about 500 °C because of a greenhouse effect, a conclusion confirmed by Mariner 2 in 1962.
- Carl Sagan inspired a generation of science communicatorsCarl Sagan invited a 17-year-old Neil deGrasse Tyson to Cornell and taught Bill Nye astronomy, inspiring a generation of scientists and science popularisers.
- Carl Sagan showed Mars's changing colours were dustMany astronomers thought seasonal colour changes on Mars were spreading vegetation. Carl Sagan showed they were shifts in surface dust driven by windstorms.
- Carl Sagan asked Voyager to photograph the Pale Blue DotAt Carl Sagan's urging, Voyager 1 turned its camera homeward on February 14, 1990, and photographed Earth from about 6 billion kilometres away as a tiny pale blue dot.
- Carl Sagan designed humanity's first message to the starsGiven just three weeks by NASA, Carl Sagan and Frank Drake designed the Pioneer plaque, a message to any alien finders, now leaving the solar system aboard two spacecraft.
- Carl Sagan made the search for alien life respectableIn 1982 Carl Sagan published a petition in the journal Science supporting the search for extraterrestrial intelligence, signed by 70 scientists including seven Nobel laureates.
- Carl Sagan chaired the Voyager Golden Record committeeFor the Voyager probes launched in 1977, Carl Sagan chaired the committee that chose the Golden Record's contents, including greetings in 55 languages and 116 images of Earth.
- Carl Sagan warned Congress about climate change in 1985Drawing on his study of Venus, Carl Sagan testified to the US Congress in 1985 that the greenhouse effect would change Earth's climate.
- Kip Thorne helped Carl Sagan imagine Contact's wormholesFor his 1985 novel Contact, Carl Sagan asked his friend Kip Thorne how a wormhole might work. The book sold 1.7 million copies in two years and became a 1997 film.
- Carl Sagan's Cosmos reached 500 million peopleCosmos: A Personal Voyage, first broadcast in 1980, has been seen by at least 500 million people in 60 countries, and its companion book was the best-selling science book of its time.
- Carl Sagan won a Pulitzer Prize for The Dragons of EdenCarl Sagan's 1977 book The Dragons of Eden, on the evolution of human intelligence, won the 1978 Pulitzer Prize for General Nonfiction and introduced his Cosmic Calendar.
- Carl Sagan gave the public a baloney detection kitIn The Demon-Haunted World (1995), Carl Sagan offered readers a toolkit for critical thinking and popularised the rule that extraordinary claims require extraordinary evidence.
- Carl Sagan warned the world about nuclear winterIn 1983 Carl Sagan co-authored the TTAPS study warning that a nuclear war could cool the planet, work honoured in 2022 with the Future of Life Award.
Sources
- Carl Sagan Wikipedia
- Carl Sagan The Planetary Society
- Europa Clipper Wikipedia
Another act of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.