Kepler spacecraft has been searching for planets in a particular region of our galaxy. It does this by monitoring the change in brightness of these stars when planets cross in front of them. In December 2011, Kepler discovered a planet in the “habitable zone” (Kepler-22b) that was 2.4 times the size of our planet, earth. The habitable zone is the zone near a star which is the right distance for life to exist. If it is too close, it will be too hot for water (if present) to exist as a liquid and for life to evolve, while if it is too far, it will too cold and water will exist as ice, preventing evolution from occurring.
Kepler has now discovered the tiniest solar system known so far. It comprises a single red dwarf and three small planets that are half and three-quarter the size of the earth. The smallest of the planets has a surface temperature of 400C and it is about the same size as Mars.