Planets Ranked in Order of Habitability

Now awaiting space-condo booms in Gliese 581 system, Mars.

An American study has ranked planets according to the likelihood that they can sustain life, with our neighbour, Mars, ranking pretty close to the top. The study, undertaken by researchers at the University of Washington, used two indices to measure a slew of planet's habitability. The first index, the Earth Similarity Index, gave a score to planets based on, well, how similar they are to Earth, taking into account the planets' size, mass, and temperature. The other index, the Planetary Habitability Index, examined whether the elements required for life – oxygen, nitrogen, water, and more – were present, how much energy the planet had, and the make-up of the planets' surfaces. After assigning scores, the team determined that Gliese 581g, a planet in the Gliese 581 system, was the most likely to support life. Two other planets in the Gliese system, Gliese 581d and Gliese 581c, came in second and third. The Gliese system is about 20 light years away, so getting there might be a bit difficult once humanity inevitably ruins this planet, but Mars, which is just down the planetary street, relatively, was deemed the fourth most habitable planet. Mercury came in fifth, the moon seventh, and Venus 10th, while the Gliese system had two more entrants at eighth and ninth.