219 Minutes on Titan
On an uncharted world, a little spacecraft saw a lot in a very short time.
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Savor the pictures on the next few pages. [The images are in the magazine. Wm] Spend some time with them. They're as rare and precious as anything ever returned from space, and we're not likely to get more for a very long time. The images were taken last January by the European Space Agency's Huygens probe as it parachuted to a soft landing on Saturn's moon Titan, three-quarters of a billion miles away. As the 700-pound craft descended for two and a half hours through Titan's orange smog, swaying gently beneath its parachute, it turned slowly around its axis so onboard cameras could take in the full 360-degree panorama below. Before landing, it switched on a feeble 20-watt lamp to illuminate Titan's dark surface. Scientists hadn't expected to see much until Huygens got down to about 200 yards-sunshine on Titan being 1/1,000 what it is on Earth. But when the craft had reached about 20 miles, the first features of an alien landscape came into view.
Jonathan Lunine, a University of Arizona planetary scientist who had spent much of his career anticipating that moment, still marvels at the images, especially considering that they were taken "from a swinging platform, in the haze, in the equivalent of what would be deep twilight on Earth, of something that has the brightness of an asphalt parking lot."
Another member of the Huygens camera team, U.S. Geological Survey scientist Laurence Soderblom, laughs at the idea that anyone could be disappointed with the photos. "People want to know why they don't look like they came out of Life magazine!"
Huygens transmitted pictures and data from the surface for one hour, 12 minutes, and nine seconds, far longer than expected. A stick-like penetrator poked into the ground to test its firmness. Another instrument heated up the soil, a process that immediately triggered a release of gas, suggesting the presence of liquid methane not far below the surface. The scientists liken the landing site to a dry stream bed.
It may be dry today, but the descent pictures clearly revealed branching river channels, evidence of rain and erosion in some distant-or perhaps even recent-past. Huygens showed the landing site to be "a very strange but weirdly Earth-like area," says Lunine.
Strange is right. It's hard to get your head around Titan. The temperature is -290 degrees Fahrenheit, about the same as the temperature inside the space shuttle's liquid oxygen tank. In this frigid world, the bedrock is hard water ice. Methane is a thin, gasoline-like liquid that occasionally rains on the ice mountains and washes down smog particles, which then settle over the landscape like a black film. Instead of molten rock, volcanoes ooze what scientists call a cryolava-a mixture of water and ammonia. At Titan's temperatures, the stuff would be as thick as warm taffy.
Lunine and other Huygens team members are still poring over the 219 minutes' worth of Titan images, and expect to learn more from the Cassini orbiter, which dropped off the probe last December and is still circling Saturn. In October Cassini will fly over the landing site and make the first radar images; these will help scientists interpret what they saw in January.
Meanwhile, Lunine, Soderblom, and the rest have a total of 606 pictures taken by the one and only spacecraft ever to land in the outer solar system. No follow-up visit to Titan is currently planned. Lunine says that as he watched the pictures come up on a screen in the Huygens mission control room in Germany on January 14, "the first thought that came to my mind was incredible elation. And the second was depression, because I was seeing all the [close-ups of Titan] I'm going to see until I'm an old man. If I'm lucky."