Thursday, December 8, 2011

A Habitable Exo-Earth?

The search for terrestrial, Earth-like planets has really been heating up over the last decade or so, since we've been able to find planets orbiting other stars. So far we have identified three types of exoplanets: gas giants, hot-super-Earths in close orbits, and ice giants. The discovery of smaller, terrestrial planets has been a challenge. NASA has been using it's Kepler mission to discover planets and planet candidates. This mission is "specifically designed to survey a portion of our region of the Milky Way galaxy to discover dozens of Earth-size planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets." The "habitable zone," or "Goldilocks zone," is the not-too-hot, not-too-cold region around a star where water is able to stay in a liquid form (see above picture). Kepler identifies these planets using the transit method, measuring dips in the brightness of stars when a planet crosses in front of them (see the post Exoplanet Extravaganza for more on the methods of planet finding).

There has been a lot of buzz this week about NASA's report that the Kepler mission has found it's first planet in the habitable zone. The newly confirmed planet is called Kepler-22b and it orbits in the habitable zone of a star that is similar to our sun, a G-type star. Kepler-22b is 600 light years away from us, has an orbit of 290 days around it's star, and measures about 2.4 times the radius of Earth. This makes it the smallest planet yet found in the habitable zone of such a star. Previous research has suggested that such a planet is out there, but we had yet to find and confirm that one actually exists. We have found planets that orbit on the edges of the habitable zones, similar to Venus and Mars, around smaller, cooler stars. But Kepler-22b orbits right smack in the middle of it's star's habitable zone.

What's the climate like on Kepler-22b?  It hasn't been determined if the planet has a predominately rocky, gaseous or liquid composition. The planet's temperature is probably around 72 degrees Fahrenheit, but it is unknown if the planet has an atmosphere and what it is composed of. To say whether or not it is truly Earth-like this is information we need to know. At the moment, speculations are running a bit wild, from it might not even have a surface to ideas about how civilizations have evolved there. I suppose that type of thing goes along with the discovery of the first anything.

The Kepler Mission has also discovered 1,094 other new planet candidates, bringing Kepler's total planet number up to 2,326. Of these, there are 207 that are approxiamtely Earth-size, 680 that are super Earth-size, 1,181 that are Neptune-size, 203 that are Jupiter-size, and 55 that are larger than Jupiter. These planets are just waiting for follow-up observations to verify that they are actual planets. Kepler-22b is the first to receive this confirmation. In addition to Kepler-22b, there are 48 other planet candidates in their star's habitable zone. It should be exciting to find out more details about these planets too!

I don't have a paper to cite for you on this one, but one is expected to be published soon in The Astrophysical Journal. Results will also be presented at the first Kepler Science Conference this week at NASA's Ames Research Center.

Until then here are some sources to get you started...
Find out more about the NASA's Kepler Mission.
Read NASA's News Release on Kepler-22b: "NASA's Kepler Confirms Its First Planet in Habitable Zone"
McDonald Observatory Release: "NASA Mission, Texas Astronomers Collaborate to find Goldilocks Planet, Others"
Washington Post: "NASA finds new planet Kepler 22b outside solar system with temperature right for life"
ABC News: "New Planet: An Earth-Like World, 600 Light-Years Away?"
The Telegraph: "Kepler 22b: probably not home to interesting aliens"

(image c/o NASA)

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