LAKES of methane may cover around three-quarters of Saturn鈥檚 moon Titan, according to radio echoes from this mystery world. So the European Space Agency鈥檚 Huygens probe could be heading for a splashdown when it parachutes down to the moon鈥檚 surface in January 2005.
Ever since the Voyager fly-bys of the 1980s, scientists have wondered whether pools of liquid hydrocarbons exist on Titan. But proving it has been difficult because the moon is shrouded by a thick nitrogen-rich atmosphere, which blocks the view of its surface at optical wavelengths.
Rough maps from infrared observations of Titan鈥檚 surface hinted mainly at water ice. But other measurements have shown methane clouds growing and shrinking in the atmosphere. Now Donald Campbell of Cornell University, New York, and his colleagues have used the 305-metre Arecibo dish in Puerto Rico to bounce a powerful microwave beam off Titan, and listened for the faint echo.
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In three-quarters of the reflections, they picked up signals that sounded as if they had been bounced off flat surfaces, tens to hundreds of kilometres in diameter. But the surfaces are not reflective enough to be ice. 鈥淪uch a poorly reflecting surface is characteristic of liquid hydrocarbons,鈥� says Campbell. The paper has been published online by Science ().