Tantalising Titan

The Cassini spacecraft has been keeping an eye on Titan for a while now. Titan has wind, rain, seasons, sand dunes, lakes, shorelines. But with surface temperatures of −179 °C, Saturn's largest satellite - the only natural satellite in the solar system with a proper atmosphere - is way too cold for water. Below its ice crust, however, it looks like there might be an ocean of liquid water thanks to the presence of ammonia. Where there's water, there may, just may be life. An even more exotic possibility is the idea of life forms adapted to liquid methane or ethane, of which Titan has plenty of lakes on its surface. 

An image Cassini took on 12 May 2007 reveals that Titan has seas, shorelines, islands, bays, channels and peninsulas, much like the Earth (image source: NASA).

'In 2005', reports the New Scientist, 'Chris McKay of NASA's Ames Research Center in Moffett Field and Heather R Smith of the International Space University in Strasbourg, France, calculated that such microbes could eke out an existence by breathing in hydrogen gas and eating the organic molecule acetylene, creating methane in the process.' That would translate into a lack of acetylene and hydrogen near the surface. Now, the Cassini probe has found exactly that kind of evidence.

Above, Titan's sand dunes; the bright spots are not clouds but surface features. Below, for comparison, terrestrial sand dunes in Namibia (both images: NASA).

Prudently enough, scientists are quick to emphasise that the same evidence could be be produced by chemical, rather than biochemical, reactions. But the mere possibility that Cassini's measurements might be a sign of life elsewhere in our solar system has fired up the imagination of scientists and space afficionados around the world. No-one has seriously suggested anything more complex than microbes, but of course proof of any form of life, no matter how simple somewhere other than our planet would be sufficient to convince anyone (except possibly Creationists and their ilk) that the Earth is not the universe's elect planet, uniquely blessed - or cursed - with life. Plus, the mere notion that Titan's low gravity and highly dense atmosphere would allow humans to fly if they simply attached artificial wings to their arms is dizzyingly exciting.

Three false-colour snapshots of Titan, taken by Cassini in October 2005, December 2005, and January 2006 reveal a highly dynamic atmosphere over the south pole (image source: NASA).

(Article sources: New Scientist, Wikipedia, NASA)