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It now seems slightly less likely that the surface and atmosphere of Titan are shaped by cryo-volcanism, the eruption of ice caused by the internal heat of the satellite. Until now the phenomenon was thought to be quite likely on Titan, especially in a region known as "Sotra Facula".
But in the April edition of Icarus, two NASA researchers, Jeff Moore (Ames Research Center, Moffett Field) and Robert Pappalardo (Jet Propulsion Laboratory, Pasadena) show how all the surface features of Titan can be explained by the action of the atmosphere (rain and wind), of liquid flow (lakes and rivers) and meteorite impacts.
Cryo-volcanism was thought to be the mechanism that replenished Titan's dense atmosphere with nitrogen and methane, but from the data so far analysed from the Cassini probe it looks like the inside of the satellite is just too cold to generate any significant geological activity. It therefore looks like the surface features, at least in relatively recent times, have been shaped principally by meteorological effects.
Comparing radar maps of Titan with images of the surface of Jupiter's large satellite, Callisto, Moore and Pappalardo point out that the two bodies are very similar, except for the absence of an atmosphere on Callisto. They have similar dimensions and cratering patterns and lie at similar distances from their planets, in proportion to the planet's mass, and therefore experience similar tidal forces. So if Callisto shows no cryo-volcanism why should Titan?
The debate, in any case, remains open, and perhaps the final solution will come with Cassini's future flybys of Titan. A fundamental issue is whether the atmosphere can actually maintain itself without a source of replenishment from within the satellite.
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