SLUSHY water from a hidden ocean may be pooling onto the icy surface of Saturn鈥檚 moon Titan.
Titan鈥檚 exterior, where the temperature is around -180 掳C, is thought to be mostly water-ice, but it may be a different story deep down. Variations in the moon鈥檚 rate of rotation suggest an ocean could lurk below.
Advertisement
An area of Titan called Hotei Arcus appears to fluctuate in brightness on timescales of several months, and in 2005 Robert Nelson of NASA鈥檚 Jet Propulsion Laboratory in Pasadena, California, and colleagues, suggested this might be the result of 鈥渃ryovolcanic鈥� eruptions of water from below. Others argued that the flickers were caused by the moon鈥檚 hazy atmosphere.
The cryovolcanism idea was bolstered in 2008, when observations of Hotei Arcus by a radar instrument aboard NASA鈥檚 Cassini probe revealed structures that resembled lava flows. Some opponents of the idea still argued these might be deposits of sediment, carried by a flow of methane in the past.
Now radar images from Cassini have allowed scientists led by of the US Geological Survey in Flagstaff, Arizona, to create a 3D view of the area, which he presented at the Lunar and Planetary Science Conference on 24 March. It turns out that the sinuous structures tower 200 metres above their surroundings. They say that this is consistent with the structures having formed when slushy water and ammonia squirted onto the surface and froze 鈥� but that they could not have been produced by a flood of liquid methane depositing sediment.
鈥淭he structures may have formed when slushy water and ammonia squirted onto the surface and froze鈥�
If slush volcanoes have been erupting recently, Titan would join a select group of solar system objects 鈥� Earth and Io 鈥� known to be volcanic at present.
The idea of any life surviving in the erupted water is 鈥減retty much out of the question鈥�, Kirk says, as it would freeze. As for the ocean below: 鈥淲ho knows?鈥� he says. 鈥淚t鈥檚 conceivable life could be going on down there.鈥�
Jeff Moore of NASA鈥檚 Ames Research Center in Moffett Field, California, says it鈥檚 still not obvious that the structures flowed. 鈥淲e haven鈥檛 seen any unambiguous evidence [of volcanism] yet.鈥�
