Today sees the announcement that one of the "candidate" planets listed from NASA's Kepler mission back in February is now confirmed, and it's a key one. At 2.4 times the diameter of the Earth the planet Kepler 22-b also orbits its parent star (which is a slightly less massive G-dwarf star than the Sun and 25% less luminous) in 290 Earth-days, which places it within the nominal "habitable zone". This system is about 600 light years from us.
This confirmation is one of a host of new results, as well as many new candidates. Altogether Kepler now has a staggering list of 2,326 possible planet detections, 207 of which are close to Earth in size and 680 are "super Earth" sized (i.e. up to about 10 times as large).
Interestingly, Kepler 22-b showed up as a transit signature just 3 days into Kepler's science observations back in 2009, but the protocol is to wait for 3 confirmed transit events before calling a detection a bona-fide confirmed planet.
So here it is, arguably a much better candidate than some others we've heard about over the past 36 months (including the seemingly ill-fated Gliese 581 g that was claimed to be an Earth-like world). But as always there are many ifs, buts, and maybes. The habitable zone is estimated (with variations in method) assuming that a planet has an Earth-like atmosphere, since the greenhouse effect is a vital ingredient in setting the surface temperature to between 0 and 100 Celsius (freezing and melting point of water). And of course, for there to be liquid water on the surface (an assumed critical factor for life as we know it - as a biochemical-solvent and essential part of geophysical and climate cycles) there has to be water. Neither of these two basic items are known to exist in this case, and so as glorious as Kepler 22-b is, it represents the tip of the iceberg (no watery pun) in terms of what's coming next and what we need to do next - which is get our hands on spectroscopic measurements of Earth-sized and super-Earth sized worlds.
How are we going to do that? Well, first we really need the James Webb Space Telescope to launch, and then it would be really, really cool if we could have something like the New Worlds Mission launch along with it...