Early next year a European space probe called Huygens will complete a seven year journey by crashing into the thick, freezing atmosphere of Saturn’s moon Titan at 5,92km a second. It will open a parachute and drop into a fug of nitrogen, methane, alcohol fumes, ammonia and ice.
It will be a brief encounter with the largest single unexplored piece of real estate in the solar system, Ralph Lorenz of the University of Arizona told the American Association for the Advancement of Science in Seattle.
”We think Titan is mostly rock and ice,” he said, ”including a deep-water ocean under an icy crust. It also has a thick atmosphere. That makes it unique among the moons of the solar system.”
Titan is about half the size of Earth, but with an atmosphere four times as dense. Its temperature is minus 179C. Images from the 300 metres wide Arecibo radio telescope in Puerto Rico — the largest on Earth — indicate that there could be lakes on the surface, containing not water but liquid methane. One of the products of the destruction of methane is ethane.
The Huygens probe is aboard a US mothership, Cassini, which was launched in 1997.
Cassini will pass between the rings of Saturn on July 1, and on Christmas Day it will deliver Huygens on a slow trajectory to Titan. On January 14, the lander will hit the surface of Titan at around five metres a second. If it survives, it will radio its data back to Earth across 1 120-million kilometres of space.
Titan matters because it is rich in organic chemicals that on Earth would have been the precursors to life. So the details of its surface and atmosphere could throw light on the origin of life on Earth, and the possibility of life elsewhere in the galaxy.
”I think we will see a sort of rugged, but muted landscape. It doesn’t have the same kind of freeze-and-thaw shattering process to give lots of sharp features. It will be a rounded landscape,” Lorenz said.
”We’ll see a lot of impact craters, and most will be filled with liquid to form circular lakes, bull’s-eye lakes, horse-shoe lakes. So I think we’ll see something maybe a bit like Sweden or northern Canada.”
If Huygens hits something hard, the mission will end abruptly. If the probe splashes down in snow or liquid, it might transmit for half an hour before perishing in the moon’s icy embrace. But the adventure will provide lessons for both astronomers and biologists.
One day, Titan will get its place in the sun. In about five billion years, the sun will begin its death throes by swelling to a red giant, incinerating the Earth and the nearest planets, but warming Titan’s atmosphere and triggering a greenhouse effect. For about 500 million years, Titan will thaw into a waterworld.
”That is not the sort of world where you or I would choose to live, but it may prove favourable to the origin of life,” Lorenz said. ”That may well be replicated throughout the galaxy right now.” – Guardian Unlimited Â