There could be rain in the forecast on Titan--huge torrents of it, swelling rivers and filling seas. But nothing's likely to grow on the surface of that distant moon of Saturn. The temperature averages a brisk -290 degrees F, and the rain is not water but liquid methane. Those are just some of the findings of the remarkable Huygens spacecraft, which landed on Titan two weeks ago. The probe took seven years to fly to the Saturnian system and lived, as planned, for only 70 min. on Titan's plains. But the data it radioed home in the eyeblink of its active life should keep investigators busy for years.
The space community had good scientific reason to want to visit Titan. Larger than Mercury and Pluto, it is dense with organic chemicals, just the kind of prebiotic broth believed to have given rise to life on Earth, though Titan's bitter cold would have flash-frozen any biological processes before they got started. "Titan is so cold that the water is frozen out, whereas here it's liquid," says Jonathan Lunine, a mission scientist. "But that's why it's probably such a good snapshot of early Earth."
To find out, the 9-ft., 700-lb. Huygens hitched a ride aboard the 6-ton, 22-ft. Cassini orbiter, which reached the Saturnian system last summer. On Christmas Eve, Cassini lobbed Huygens toward Titan, and on Jan. 14 the probe reached the moon, slamming into its atmosphere at 13,000 m.p.h. Throughout a 147-min. parachute descent, Huygens took pictures and sniffed the air. After it landed, it switched on the remainder of its six instruments. What it saw was not very welcoming.
If Titan is a chemical cousin of Earth, it's an Earth gone terribly wrong. The surface is etched with riverbeds and shorelines carved by the methane rains. The ground seems to be a thin, frozen crust over a smoother, softer layer. "Kind of a creme brulee consistency," says John Zarnecki, a principal science investigator. The atmosphere produces plenty of wind and weather, and there is even a flicker of a greenhouse effect, but with sunlight a thousand times dimmer than on Earth, it doesn't amount to much.
Scientists will have all the time they need to tease out richer science from the data that Huygens left them. As even a few pictures show, they have plenty to work with. --Reported by Dan Cray/Pasadena and Ursula Sautter/Darmstadt, Germany