Scientists have abandoned hope of finding life—or any indications that it once existed—on the earth's own desolate moon. But what are the chances of uncovering any signs of life on more distant moons? Focusing their telescopes on satellites of Saturn and Jupiter, astronomers have now discovered evidence that in at least one case suggests that primitive life may indeed exist elsewhere in the solar system.
That possibility was suggested in a recent study of Titan, the largest of Saturn's ten moons, by a team of Cornell University scientists under Astronomer-Exobiologist Carl Sagan. From infra-red and other telescopic measurements of the satellite, a body as large as the planet Mercury, Sagan and his colleagues conclude that Titan is relatively much warmer (about—100° F.) than previously estimated. It also has a thicker atmosphere than had been suspected and is leaking small quantities of hydrogen gas into space. Pondering these surprising conditions on Titan, the Cornell group has evolved a picture of a strange and turbulent world.
Time Machine. To account for the higher-than-expected temperatures on a body that is about ten times farther from the sun than the earth is, Sagan explains that Titan's atmosphere must be producing a significant "greenhouse effect"—that is, trapping more heat under its clouds than it radiates back into space. He speculates that those clouds may consist of rust-red organic compounds floating in a thick atmosphere of hydrogen, methane and ammonia coughed up by volcanic eruptions. Exposed to the sun's radiation, the gases could form into complex organic compounds, including sugars, purines and even amino acids. Such a mix of ingredients is akin to the primordial "soup" that is believed to have given rise to the first life on earth.
"Titan is a kind of time machine," says Sagan, "enabling us to look backward to the time of the early earth. I don't think life there is out of the question."
The other findings involve Europa and Ganymede, two of Jupiter's twelve moons. According to spectroscopic observations made at Arizona's Kitt Peak National Observatory by a team under M.I.T.'s Carl Pilcher, both bodies seem to be covered by large areas of water ice similar to earthly frost. Two other Jovian moons, Callisto and Io, also show signs of frost particles, but the evidence is slightly less certain. While the discovery of water on Jupiter's four inner moons does not necessarily mean that life forms exist on any of them, the scientists noted, it increases the possibility.