Are some planets more habitable than Earth ?

Astronomers seeking signs of alien life are on the lookout for 'superhabitable' extrasolar planets.

In the hunt for habitable alien worlds astronomers have been particularly keen to look for signs of planets that exhibit similarities to our own, but now astrobiologists have suggested that what we should be looking for are planets that are even more habitable that the Earth is.

"From a potpourri of habitable worlds that may exist, Earth might well turn out as one that is marginally habitable, even bizarre from a biocentric standpoint," wrote researchers René Heller and John Armstrong who put forward the idea.

A 'superhabitable' world would most likely be older and larger than the Earth, while water and gases most commonly associated with signs of life ( such as oxygen ) should also be present. Planets located more towards the center of their sun's habitable zone might also yield a higher potential for habitation than those, like the Earth, that lie near the edge.