Carl Sagan’s Cosmic Legacy

November 9 is Carl Sagan Day when enthusiasts of astronomy and science remember and celebrate the life and works of Carl Sagan. Why is Sagan honoured in this way? Let us look back at the man and his career.


Image of Sagan and Viking

Man meets robot A full-scale replica of a Viking spacecraft is displayed by Carl Sagan. The super optimistic Sagan hoped the Vikings might discover Martian fauna as big as bears and proposed that the probes carry bait to lure them closer. This suggestion was not acted on. (Image Credit: NASA)


It seems impossible to research the Solar System and not encounter Sagan’s name as a major contributor to human knowledge. Among many other things, he predicted the hellish greenhouse of Venus, the lakes of Titan and the subsurface seas of Europa. If you look beyond the Solar System you will find the Pioneer and Voyager probes hurtling outwards carrying messages of greeting for any extraterrestrials they should encounter. Carl Sagan had these cosmic postcards put there and was instrumental in their formulation. Even further away, currently almost 40 light years from our world is the Arecibo Message, radio waves carrying 1679 binary digits making up a carefully crafted missive to the Hercules Globular Cluster (M13). Sagan helped write the Arecibo message which will reach its destination 25 000 years from now.

Born on 9 November 1934 in New York, Sagan had a happy childhood. Visits to museums and the planetarium, together with a voracious appetite for books on science and science fiction led to a deep and lasting fascination for the mysteries of the universe. By the mid-1950s, the young Sagan was studying astronomy at the University of Chicago. His list of interests was as wide as the cosmos, in his papers and books, he theorised on the compositions the atmospheres of Venus, Mars, Jupiter and Titan, speculated on the possibilities of interstellar travel and communication, considered the origin of life on Earth and even how the human mind had evolved.  Carl Sagan was a renaissance man born centuries too late!

Sagan’s career blossomed just at the right time in human history, the planets and moons of the Solar System were no longer just specks of light shimmering in telescope eyepieces but worlds to be visited, scanned and photographed at close range by robot explorers from earth. Sagan’s enthusiasm for and knowledge of our neighbouring worlds made him very useful. From the 1960s until the mid-1990s, it is hard to find any NASA mission to the planets that Carl Sagan did not advise, promote or analyse. Sagan speculated on what the probes would find and how they should be targeted to maximise their scientific return. The Mariner, Viking, Pioneer, Voyager  and Galileo missions were made all the richer for his input.


The plaque attached to the Pioneer spacecraft designed by Carl Sagan and Frank Drake (Image credit: NASA/JPL/artwork by Linda Salzman Sagan

The plaque attached to the Pioneer spacecraft designed by Carl Sagan and Frank Drake (Image credit: NASA/JPL/artwork by Linda Salzman Sagan


In the early 1970, the quiet and bookish young scientist made the surprising transition to media superstar. He wrote several popular books, lucid and poetic sprinkled with delightful similes and metaphors. Reading them made the universe a bright and inviting place. Coming at a time when there was very little popular science published, his books found a vast audience. In 1977 he was the presenter of the annual Royal Institution Christmas Lectures, where, equipped only with a few simple props, slides and his amiable personality, he took the juvenile audience (and millions of TV viewers) on a thrilling voyage through the planets. His outreach to the public, led to appearances on chat shows where his good looks, enthusiasm and charm won over audiences with little interest in science. Eventually he wrote and presented the wonderful TV series Cosmos. Visually stunning, this was a huge international success; it is still available on DVD and his book to accompany it is still in print. A new version of Cosmos fronted by Neil Degrasse Tyson was broadcast in 2014. More books followed throughout his life, including his science fiction novel Contact, adapted into a film starring Jodie Foster.

Although loved and admired by many, Sagan was not universally popular. Some snobs in the scientific establishment sneered at his wide-range of scientific interests, suggesting he was a “lightweight”. Other scientists looked on his engagement with the public as vulgar self-promotion. Possibly thanks to these critics he was never made a member of the National Academy of Sciences.  Initially open to the possibilities of extraterrestrial  encounters, after examining the evidence, he expressed intense scepticism of reports of alien visitations and other claims of fringe science. The “ufologists” never forgave Sagan for this and often claim he knew the truth about alien visitations and was conspiring to withhold the facts.

In 2000 there was surprise when it was revealed that Sagan was one of a team of astronomers who worked on Project A119, a 1958 USAF plan to detonate a nuclear bomb on the Moon as a propaganda stunt. Thankfully this Strangelovian scheme was not proceeded with. Sagan’s involvement with the plan (which he does not seem to have discussed publicly) was especially shocking as he was later known as a staunch supporter of many left of centre causes. Sagan’s opposition to the nuclear arms race twice led to his arrest for trespassing on nuclear test sites in the 1980s. Eventually, his research on planetary atmospheres led him to conclude that the ash that would be released as cities burned in a nuclear war could so obscure the Sun as to plunge the world into a “nuclear winter” dooming humanity. Coming at the chilling early eighties height of the Cold War, at a time when the Soviet and US military establishments were claiming that  World War Three could be fought and won, this bleak hypothesis won him no friends among US politicians. Thankfully, the nuclear winter hypothesis was never been tested. Sagan’s personal life was also troubled; he had two previous wives before his final marriage to Anne Druyan.

Sadly, Sagan passed away on 20 December 1996. He did not live to see the surface of Titan as seen by the Huygens lander or any other amazing results from the Cassini mission. Nor did he get to add his interpretations of the spectacular MRO images of Mars. He was not here when the number of discovered exoplanets went over 3000. He would have loved to hear of these discoveries as they would have made the Universe even more wonderful to him. We will never know how human knowledge would have been broadened by his insights on these and so many more recent revelations from space. Carl Sagan’s passing was a loss for us all. But he left us a marvellous legacy; his words which will continue to inspire as long as people gaze into the deep dark night sky.

(Article by Colin Johnston, Science Education Director)