Kepler observes a two-planet system

Statistically speaking, a great deal of luck is needed to be able to observe a planet transiting its star as this requires perfect alignment between the star, the planet and the observer. However, this is the method that has been adopted for the French satellite CoRoT belonging to the CNES and NASA’s counterpart Kepler. Both detect exoplanets by measuring the variations in luminosity induced as the planets pass in front of their star and NASA has just announced that Kepler has marked up a double success: two planets around the same star. There is even perhaps a third one…

Both planets, the size of Saturn (80 and 54 times the mass of the Earth), are orbiting a yellow star renamed “Kepler 9”, slightly larger than our Sun and situated in the Lyre constellation, about 2,300 light years from the Earth. These planets complete their orbits in 19.2 and 38.9 days, which tends to indicate that there is gravitational resonance between them. A third planet, a “Super-Earth” about 1.5 times bigger than our planet might be following an orbit very close to the star, with a 38-hour revolution, but this remains to be confirmed as the slight variations in luminosity that indicate its presence could also come from parasite sources such as a star companion or other stars in the background.

In seven months, Kepler has observed variations in luminosity for more than 156,000 stars and detected about 700 potential planets, of which seven have been confirmed by observations from ground observatories.