Carl Sagan's is the all-American story of the child of immigrants who achieves fame and riches through good looks, hard work and talent. He became a salesman of scientific ideas. Such was his gift for communication that this author of a score of popular science books is scarcely remembered as a scientist in his own right. Sagan's work on the atmosphere of Mars and Venus gained him a role in Nasa's unmanned missions to those planets during the 1960s and 1970s. When he appeared on The Johnny Carson Show to explain what the probes had seen, America found a spokesman for science and Nasa one for its cause.
When Nasa tired of planetary exploration and turned to the space shuttle, Sagan began to write. His books range from The Dragons of Eden to Pale Blue Dot, his late musing about our place in the universe, and cover topics from evolution to intelligence. He made the renowned public television series, Cosmos. He essentially invented the scientific field of "exobiology", the study of life beyond the Earth. The necessarily speculative nature of the subject gave Sagan licence to roam through astronomy, chemistry and biology. It also gave scientists whose researches were more narrowly focused an excuse to attack him for his success.
One would say that Sagan's life provided enough material for two biographies if these books were not so similar. Any writer must envy the ability that Sagan developed to dictate "um-less" prose on to tape that led to so many best-sellers. He had a way of doing things that caught the public imagination. It was not he who suggested putting plaques on Nasa's planetary probes containing images of the human figure and evidence of human ingenuity. It was not he who first suggested that there might be a greenhouse effect on Venus and dust storms on Mars. He never made a true scientific discovery. He didn't actually gather data. It was not he who first designed the experiment or ran the computer model that showed that the smoke thrown up into the stratosphere from even a small-scale exchange of nuclear weapons might produce global cooling sufficient to destroy agriculture. And he didn't provide the catchy label of "nuclear winter" by which this scenario became widely known. But Sagan was pivotal in bringing all these topics to broader attention. In the case of the nuclear winter studies, this was at some risk to his relations with Nasa and at some cost, too: his book on the subject was his most substantial work - and the least read. Nevertheless, the name of Sagan was undoubtedly a factor in bringing world leaders round to a new position on nuclear arms. Comments from Ronald Reagan, in a 1985 interview in the New York Times, steal from Sagan's writing. Mikhail Gorbachev personally assured Sagan that he had read him and that his views were shaping his policy.
Keay Davidson calls Sagan "the Leonard Bernstein of science", "a Mr Science for the hip". He was. But William Poundstone is more perceptive when he says that Sagan was also "science's Tom Sawyer, capable of convincing others that whitewashing his fence was the most fascinating of all possible demands on their time". Both biographies examine infamous episodes when Sagan was passed over for tenure at Harvard and, later, membership of the National Academy of Sciences because of what more "serious" scientists saw as extra-curricular activities. Both are rather similar in style, too - slick and earnest.
People who have read Sagan's major books will find surprisingly little that is new here. Perhaps these biographies will reach a different audience. With an early death plucking at his sleeve, Sagan came to see that his consistent belief in extraterrestrial life (but not in UFOs, which he was keen to debunk along with a lot of other pseudo-science) was really about us here on Earth. Sagan's liberal-ism may have been simplistic and naively based on scientific rationality, but it reached millions who would otherwise not have heard. Now those who missed Sagan's message first time around have a chance to hear it. The plaques on the Pioneer and Voyager spacecraft - the first human artefacts to press beyond the solar system - will never be read by an alien civilisation. They were meant for our own.