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Cassini spots tropical lagoons on Titan

Paul Sutherland, Feature writer
Jun 15, 2012, 7:00 UTC

Sen—Planetary scientists have been surprised by the discovery of exotic lagoons in the tropics of Saturn's largest moon Titan.

These are not sun-kissed holiday spots however, but long-standing little lakes of methane beneath the satellites poisonous smog.

They come as a surprise because it had been thought that such wet areas would be found only around the poles due to circulation patterns within Titan's atmosphere.

Titan fascinates because, despite the unfriendly nature of its chemistry, it shows remarkable similarities to surface features and weather on our own planet.

This is largely because this distant moon is the only satellite in the Solar System to have a dense atmosphere. There it rains methane rather than water, with the liquid circulating in a way similar to the Earth's hydrological cycle.

Europe achieved a major space success in 2005 with the soft-landing of a space probe, Huygens, which had been carried there by NASA's Cassini mission to Saturn. The lander sent back pictures and other data about the region where it landed that suggested it might be a damp former lake bed with a consistency similar to creme brulee.

Now Cassini visual and infrared mapping spectrometer, operated by the University of Arizona, Tucson, has detected dark areas in a region of the tropics named Shangri-La that is not far from where Huygens touched down. It is thought that many of these are long-standing, ankle-deep puddles but that some could be methane lakes at last a metre deep.

The Cassini team had been surprised by the large amounts of methane on Titan where it is broken apart by ultraviolet light beginning a chain of complex organic chemical reactions.

Titan's tropical lakes

Tropical lakes observed by Cassini. Credit: NASA

Rain was not thought to fall in great amounts in the tropics. Instead it is now thought that the small tropical lakes and puddles are like oases in the desert, with the liquid methane and ethane emerging from beneath the surface.

The discovery of these new ponds on Titan is revealed this week in the journal Nature. Cassini's data suggests they have been there since at least 2004 when its instruments began their observations.

Linda Spilker, the Cassini project scientist based at NASA's Jet Propulsion Laboratory in California, said: "We had thought that Titan simply had extensive dunes at the equator and lakes at the poles, but now we know that Titan is more complex than we previously thought.

"Cassini still has multiple opportunities to fly by this moon going forward, so we can't wait to see how the details of this story fill out."