Astronomers think that Saturnian moon Titan’s unusual geological activity is down to a combination of its size, its composition and its position in Saturn’s system of moons. The second largest satellite in the Solar System, Titan is composed of rock and ice with a much lower melting point than the rocks of the inner planets – low enough for ‘cryovolcanic’ activity to gradually reshape the surface over time.
Titan’s size also allows it to retain a substantial amount of heat from the collisions that formed it. Until recently, astronomers thought that this was the main driving force behind Titan’s activity, but in 2012 maps of the moon’s gravity field from the Cassini probe showed its shape is ‘squashed’ rather than spherical. This means that different parts of Titan experience different tidal pulls from Saturn and other nearby moons as it orbits the planet over a 16-day cycle. This constant tugging at the interior is now thought to generate much of Titan’s internal heat.
Answered by Giles Sparrow