- Person
- Carl Sagan
- Lived
- 1934–1996
- Field
- Astronomy, planetary science
- From
- American
The story
For decades, observers watching Mars through telescopes saw light and dark markings that seemed to change with the seasons. A popular explanation was that the dark areas were plant life spreading and retreating as the Martian year turned. Earlier still, Percival Lowell had claimed to see canals on the planet. Mars seemed to many people a living world, and the idea had deep roots in popular culture, including the Edgar Rice Burroughs novels that had fired Sagan's own imagination as a boy.
As a planetary scientist trained by Gerard Kuiper, Sagan studied these colour variations closely. He concluded that they were neither vegetation nor true seasonal changes in the surface. Instead, he and his colleagues argued, they were shifts in surface dust caused by windstorms, covering and uncovering darker ground beneath.
Sagan was an experimenter on the Mariner and Viking missions, which transformed knowledge of Mars, and he arranged experiments on many of the robotic spacecraft that explored the solar system. The Planetary Society lists the seasonal changes on Mars, explained by windblown dust, alongside the heat of Venus and the reddish haze of Titan among the planetary mysteries he helped solve. In 1971 he joined Ray Bradbury, Arthur C. Clarke and others on a public panel later published as Mars and the Mind of Man.
His interest in Martian dust had unexpected consequences. In 1971 the Soviet Mars 2 and Mars 3 probes found a planet-wide dust cloud, with the surface much colder than the top of the cloud. Sagan sent telegrams to the Soviet scientist Georgy Golitsyn urging him to study the phenomenon. The five-member team that later modelled nuclear winter, including Sagan, had all worked on Martian dust storms or asteroid impacts, and that experience shaped their research.
Mars remained central to his public work. An episode of Cosmos was devoted to the planet, from Lowell's canals to the Viking landers. After his death, the landing site of Mars Pathfinder was renamed the Carl Sagan Memorial Station in 1997, and his former student Steve Squyres led the Spirit and Opportunity rover mission in 2004. His careful reasoning set a standard for testing exciting ideas against evidence.
Why it matters
By replacing a romantic myth with a physical explanation, Sagan helped scientists understand Mars as a real, dynamic world and plan the missions that explore it today.
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 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 foresaw ocean worlds on Titan and EuropaCarl Sagan was among the first to suggest that Saturn's moon Titan might have surface liquids and that Jupiter's moon Europa might hide an ocean of water beneath its ice.
- 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
- Nuclear winter 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.