Diameter 0.4 Earths Mass 0.02 Earths Atmosphere Nitrogen (98.4%), methane (1.4%), hydrogen (0.2%)
Titan is the only world in the universe other than Earth that we know for certain has bodies of liquid on it – in this case lakes and seas of methane and ethane, similar in composition to jet fuel. But while it might lack water, the thick atmosphere of this moon of Saturn, coupled with its Earth-like topography, makes it a tantalising prospect for life. In fact, some scientists think it might be similar to early Earth billions of years ago, when life was just starting to arise. What’s more, Titan also appears to have a salty ocean below its surface. So even if the surface is inhospitable or perhaps plays host to more exotic types of life, it could be that Earth-like life can survive underground.