"A Bounty of Midsize Planets Is Reported"

From the New York Times

About a third of all the Sun-like stars in our galaxy harbor modestly sized planets, according to a study announced Monday by a team of European astronomers.

At a meeting in Nantes, France, Michel Mayor of the Geneva Observatory and his group presented a list of 45 new planets, ranging in mass from slightly bigger than Earth to about twice as massive as Neptune, from a continuing survey of some 200 stars.

All of the planets orbit their stars in 50 days or less, well within the corresponding orbit of Mercury, which takes 88 days to go around the Sun, and well within frying distance of any lifelike creatures.

Among the bounty is a rare triple-planet system of “super-Earths” around the star HD 40307, about 42 light-years away in the constellation Pictor. The planets are roughly four, seven and nine times the mass of Earth and have orbital periods of 4, 10 and 20 days, respectively.

Dr. Mayor called the discoveries “only the tip of the iceberg” in a news release from the European Southern Observatory in Garching, Germany.

Theories of planet formation, Dr. Mayor said in an e-mail message from Nantes, hold that smaller planets like super-Earths and Neptunes should be numerous. “But evidently it was a nice surprise to see that with our instrument we have the sensitivity to detect that population,” he said.

Astronomers said the new results indicated that when their instruments got sensitive enough to detect even smaller planets, such planets would be there to be found.

Sara Seager, a planetary theorist at the Massachusetts Institute of Technology who was one of the organizers of the Nantes conference, said in an e-mail message, “We’ve always been hoping that low-mass planets are common — to increase the chance for an Earth analog to exist around a nearby star.”

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