Discovery of the first extrasolar planet potentially capable of harboring life was announced today by NASA and the Kepler telescope team. The planet, unassumingly dubbed Kepler 22-b, orbits within the habitable zone of its host star, about 15% closer than the Earth orbits our sun. Consequently, astronomers have estimated that its surface temperature likely hovers around 22 degrees Celsius, perfect conditions for life-supporting water to exist in liquid form.
The habitable zone is so named because it is the only range within which planets are likely to maintain a temperature conducive to liquid water. So far, water is the only known solvent that enables life processes to take place, although other chemical candidates have been proposed.
Kepler 22-b orbits a star similar to our own, about 600 light-years away in the constellation Cygnus. Its star emits about 25% less light than our sun, enabling its habitable zone to encompass planets with closer orbits.
A complete orbit of Kepler 22-b around its sun takes 280 days. At 2.4 times wider than Earth, the composition of Kepler-22b is a puzzle. It could be rocky, a “super-Earth” much like our own planet but bigger. Alternatively it could be a gas giant like Jupiter or Saturn, making the prospect of life taking hold less likely.
Ground-based observations to take place this summer will help confirm the mass of Kepler 22-b, enabling astronomers to determine what type of planet it is.
The total number of possible extrasolar planets discovered by the Kepler mission now stands at 2,326. Even more are likely to be announced in the coming year as time allows for additional confirmations of observed transits.