Titan

Saturn's largest moon is Titan and it is second largest moon in the solar system. Titan is much bigger than Mercury, but much less denser. Titan's atmosphere consists mainly from nitrogen and methane, little ethane thrown in the mix and the whole moon is covered in this thick atmosphere.

What makes Titan so intriguing is it's surface, it resembles that of young Earth's in many ways. Titan has lakes like here on Earth and mountains, but no vulcanic activity as we tought before. Cassini probe proved that hypothesis wrong. Read the entire story here in Finnish. There is rain fall like here on Earth, but the rain falls much more slowly, becaus of the low gravity.

What makes Titan so interesting is also the fact that, the lakes on Titan are made of  liquid methane and the rocks on  the shores are, in fact, water ice and rain on Titan is also methanenitrogen. What makes this possible, liquid methane, that is so volatile on Earth, can be liquid on Titan? It is the freezing temperature of -180°C and lack of oxygen. Liquid methane is extremely clear because it is not a good solvent like water is here on Earth. Here is more on liquid methane on Titan in english.