The Huygens probe, which will parachute onto Saturn鈥檚 largest moon, Titan, early next year, is likely to splash down in an ocean of hydrocarbon oil.
Until recently, astronomers had been unable to peer through Titan鈥檚 thick atmosphere of nitrogen and methane. But they always suspected that there must be source of methane, perhaps in liquid form, at the surface. Without such a hydrocarbon source, the methane in Titan鈥檚 atmosphere would have vanished long ago, as it is steadily destroyed by ultraviolet light from the sun.
An 8.2-metre telescope at the European Southern Observatory in Chile has now managed to pierce the clouds, using near-infrared frequencies, to reveal four vast dark areas of low reflectance on Titan鈥檚 surface that have exactly the signatures expected for smooth, flat oceans of hydrocarbons. The team has named the oceans Dragon鈥檚 Head, Dog, Ball, and Lying H after their approximate shapes.
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Huygens鈥檚 descent trajectory makes it likely that it will land in the Dragon鈥檚 Head ocean, says Markus Hartung, a member of the team that took the images. It would be the first ocean landing of a spacecraft outside Earth. Luckily, the spacecraft is designed to float, and some of its instruments are better suited to analysing liquids than solids.
