Ever since we first discovered a planet outside our solar system way back in 1988 the hunt has been on to find another planet like our own. That’s not a particularly easy quest however as the methods that we currently have at our disposal, namely the radial velocity method (looking for little wiggles in the parent star) and the transit method (dimming of the parent star from our point of view) are heavily skewed towards finding large planets close to their parent stars. Finding a planet like ours by these methods not only requires precision tools but also great lengths of time, on the order of 2 years or so to ensure that what we saw wasn’t a fluke. Thus a planet like our own has escaped our detection because we’re simply unable to detect it.
The start of this year saw some major progress with the data from NASA’s Kepler mission. Back in January I blogged about Kepler-10b which is the smallest exoplanet that had been discovered to date. Unfortunately for planet hopefuls (and the planet as well) Kepler-10b was found no where near the habitable zone of its parent start. In fact the planet orbits its star in just under a day, putting its orbital distance at around 1/20th of the distance between mercury and our sun. The surface temperature there is enough to melt iron, eliminating the possibility for any kind of life as we know it to arise there.
However the astronomers working on the Kepler data didn’t just stop there as there. Within the wealth of Kepler data are some 48 other earth-like candidates, planets with orbital periods that places them squarely in the habitable zone of their parent stars. One of those potential candidates was Kepler-22b, a planet who’s orbit is much closer in than earth to its parent star which is a lot dimmer than our own. This mean that it was just on the edge of the habitable zone and the last piece of the puzzle was how big it was compared to earth. That last piece of the puzzle was just revealed today and Kepler-22b’s radius is 2.4 times the size of earth.
Whilst that makes Kepler-22b sound like some kind of giant it’s still within the boundaries of what we currently believe to be hospitable to life. The real kicker for Kepler-22b will be finding out its mass as currently, whilst we suspect that it’s rocky like our planet due to its position, we have no idea what its actually comprised of. Right now it could be anything from a planet covered entirely in oceans to a giant rock ball with little to no atmosphere. We can find out the mass by using the radial velocity method and I’m sure that’s the next step that NASA is taking in attempting to figure out just what kind of planet Kepler-22b is.
This might be the first exoplanet to be confirmed as being within the habitable zone but what’s more exciting is the prospect that we have another 48 candidates just waiting for their confirmations to come through. What we can infer from this is that our solar system’s composition isn’t unique and that the formation of terrestrial planets like our own is quite common. That means the conditions that brought about life on our planet are also common in other solar systems which leads to the tantalizing prospect that there’s other life out there just waiting for us to discover it. Of course it will be a long time before we manage to get there and see it for ourselves but it’s still incredibly exciting and I can’t wait to see what other kinds of planets we dredge up from the next 48 potentials.