Kepler Finds A Possibly Live One

The Kepler mission has been looking for planets that might have liquid water (and therefore life as we know it) and it looks like they have their first confirmed candidate - the oh-so-memorably-named Kepler 22b.  Kepler 22b, or just 22b for short, has a radius 2.4 times as big as the Earth's and orbits a star that has roughly 2% less mass than the Sun every 289 days. That places it right at the inner edge of that star's habitable zone (the range of distances from their star where planets might have liquid water), as illustrated by this lovely NASA graphic.

If you assume an Earth-like greenhouse effect for 22b (which is a big assumption considering Venus and Mars have drastically different atmospheres than Earth), the mean surface temperature (assuming it has a surface) would be a balmy but not unreasonable 22 degrees Celsius compared to Earth's mean surface temperature of about 14 degrees Celsius.

NASA likes to call this type of planet a "Super-Earth", however that's something of a misnomer as planets with more than twice the radius of Earth probably aren't primarily rocky planets like Earth, Venus, and Mars but rather more like smaller, defrosted versions of our solar system's ice giants, Neptune and Uranus.  Using planetary structure models, one can map out the range of possible compositions for a planet of a given radius (remember with Kepler's transit data they know the planet's size but not it's mass).

As you can see, 22b likely has a composition with significant amounts of hydrogen and helium, which means it may have a very thick, deep atmosphere. Alternatively it could have very large amounts of water, but at this point there's just no way to tell what it's made of as the planet is too far from it's star to be detected using the radial velocity technique, which can determine a planet's mass.  It's possible that space telescopes like Hubble and Spitzer might be able to get some information on the composition of the planet's atmosphere, but most likely this one is going to have to wait for new telescopes and instruments to be characterized more fully.

The best part is that 22b is not alone.  The Kepler team only officially announces a planet as discovered when they can confirm it using another telescope (here they used Spitzer to verify a transit), but the list of "planet candidates" in habitable zones is growing.  As of the now, there are about a half-dozen planet candidates in habitable zones that are smaller than 22b. 

As Kepler approaches it's third anniversary, expect those numbers to increase dramatically.  You can already see the trend by comparing the numbers of planets from the June 2010 (in blue), February 2011 (in red), and December 2011 (in yellow) data releases.

You can find the official NASA press release here and the slides from that press release (which are the source of these lovely images) here.