Kepler Confirms Its First Planet in a Habitable Zone

Green area = habitable zone. Credit: NASA-JPL-Caltech

The Kepler mission confirmed the first Earth-like planet in its habitable zone. See the NASA briefing.  Its name is Kepler-22b and it is located about 600 light years away from us. This planet orbits a solar mass star (mass 0.97 times the mass of our sun) every 290 days. Its radii is 2.4 times bigger than the radius of our Earth. This means that the gravity on it will be stronger than on Earth. They say the near surface temperature of this planet is about 22 Celsius. The Kepler data so far resulted in over 2, 300 planet candidates. Out of these planets about 48 are believed to be in the habitable zone of their star.

How Does the Kepler Satellite Work?
The Kepler Satellite monitors the brightness of more than 100,000 stars for the life of the mission, which is expected to be extended beyond its current 3.5 years. The satellite was launched in March 2009. It observes the changes in brightness of these stars when planets pass in front of them. The size of a transiting planet is found from the size of its star and 'the deepness of the transit', which is the decrease in brightness of a star when a planet passes in front of it. Since Earth-like planets create 'small' dips in brightness, i.e., close to the noise level of the instrument, the Kepler mission requires three transits to declare a detection. This, of course, takes time and it is why we have to wait before even smaller Earth-like planets will be reported.