The only planet on which we know for sure that life exists is Earth. Even though this gives us just a sample of one, it is tempting to think that conditions here must be close to the ideal for life to emerge and that if there are other planets on which life exists, they must be Earth-like in terms of size and occupying the so-called ‘stellar habitable zone’ (SHZ) from its star so that the temperature range is similar to ours. [Read more…]