Back in 2005, the European Space Agency’s Huygens probe made a dramatic landing on the surface of Saturn’s largest moon Titan. During its descent through the dense nitrogen-rich atmosphere, Huygens sent back pictures of a complex landscape shaped by familiar forces.
The images showed hills and valleys, meandering rivers leading to complex deltas that eventually fed into lakes and seas with vast shorelines. Titan, it appeared, had many features in common with Earth.
But there is a crucial difference. Water plays a huge role in shaping the Earth’s surface through erosion, glaciation and so on. That’s because conditions are perfectly balanced to allow it to exist in liquid, solid and gaseous form at the same time, the so-called “triple point”.
