From Harvard:
Cambridge, MA – NASA’s Kepler Mission has discovered the first confirmed planetary system with more than one planet transiting the same star…
The inner world, Kepler 9-b, orbits its star every 19.2 days at a distance of 13 million miles, while the outer world orbits once in 38.9 days at a distance of 21 million miles. (In comparison, Mercury has an orbital period of 88 days.) They orbit nearly in resonance, with the inner planet completing two orbits for every one of the outer planet. Both are Saturn-sized gas giants, with the inner world weighing in at 0.25 Jupiter mass (80 Earths) while the outer world is a slimmer 0.17 Jupiter mass (54 Earths).
“This is the first confirmed system of more than one planet transiting the same star,” said Matthew Holman, a Kepler Mission scientist from the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. Scientists confirmed the multiple transits with radial velocity observations conducted at the W.M Keck Observatory in Hawaii.
More coverage here
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