Tuesday, January 3, 2012
Artists depiction of Kepler 11, a system with 6 known planets.
Launched in 2009, the Kepler spacecraft was designed to search a portion of the milky way for sings of other worlds. More specifically, Kepler specializes in searching for earth sized planets which, because of their relatively small size, are much more difficult to detect than the giants that have typically been identified in the past. Since it's launch, Kepler has managed to identify a total of 2, 326 potential planets orbiting around other stars in the in the tiny swatch of the Milky Way it's been tasked with searching.
When an object of a significant enough size passes in front of any star within Kepler's field of view (that's about 150,000, in case you were wondering), it causes a dip in the magnitude of light being emitted by the star. Revealing, not only the presence of any extrasolar planets around said star, but also the distance at which those planets orbit their parent star. This method of detection is commonly referred to as the transit method, and like any other method of detecting such planets, requires multiple observations for confirmation.
In the latest wave of confirmed observations, NASA announced that Kepler had identified the two smallest planets ever confirmed around another star; Kepler20-e (Diameter:11,100 km (6900 miles) and Kepler 20f (Diameter:13,200 km (8200 miles). Found in orbit around the star Kepler 20, located 950 light years from Earth in the Lyra constellation, these newly discovered Earth-sized planets join 3 other known planets in the system (Kepler 20, a,b, and c), all of which are closer in size to Neptune or Uranus. Though Kepler 20 e and f may in fact be the closet size match to Earth yet discovered, the proximity around which they orbit their parent star -which is extremely similar in size and intensity to our own sun- means they'd have average surface temperatures in the range of 800 -1400 degrees F. Making them both far from Earth-like, where their potential for habitation is concerned. That title may actually belong to another newly discovered planet that was also revealed just this month: Kepler 22b.
Found Orbiting the class G star Kepler 22, which is located around 600 light years from Earth in the Cygnus constellation. Planet Kepler 22b, was found to have a 290 day orbital cycle, which places the planet within what we have defined as the habitable zone of its parent star; which is lower in mass, and cooler than our own sun. But there's a catch. While the planet's diameter is estimated to be around 2.4 times that of Earth's, the actual mass of the planet is impossible to determine based on Kepler's observations alone. So it's impossible to say weather or not Kepler 22b is a rocky planet like Earth, or gaseous ball like Jupiter and Saturn. But if it is a world like our own, and assuming that it also has the proper atmosphere Kepler 22b would have an estimated average surface temperature of around 72 degrees F. Which would make it not only the most Earth-like world yet discovered, but also the most likely home for life as we know it outside of our own solar system. The prospect is obviously tantalizing.
To date, scientists have confirmed the existence of over 500 exoplanets * using Kepler, The Hubble Space Telescope, and various other observational techniques. As time goes on, even more discoveries will be made, and long term observations will slowly scratch all of the potential candidates off Kepler's list; possibly resulting in the confirmed discovery of several thousand more worlds orbiting stars light years away from our own. And while it will likely be some time before we ever definitively confirm that conditions on one those planets is conducive to life. The apparent abundance of stars with planetary systems would seem to suggest that it's only a matter of time before we do. And even if we can't say for certain that there's life on any of those planets, to think that we live in a time when discovering worlds in other star systems has become common place, is astonishing, to say the least.
Source: NASA1, NASA2
Image credit: Kepler 11- NASA/Tim Pyle, Kepler 20e, 20 f, and 22b- NASA/Ames/JPL-Caltech
*The exact number of confirmed exoplanets was actually kind of hard to nail down, The Extrasolar Planets Encyclopedia claims 716. But the most common figure I found was in the 500-600 range.