Trio of ‘Super-Earths’ Foretell Planet Finds
(From the September/October 2008 issue of StarDate magazine)
European astronomers have found three “super-Earths” orbiting the star HD 40307, which is 42 light-years away and slightly less massive than our Sun. The astronomers used the HARPS instrument on the 3.6-meter Telescope at La Silla Observatory in Chile.
A super-Earth is a planet more massive than Earth, but less massive than Neptune. The new planets’ masses are 4.2, 6.7, and 9.4 times the mass of Earth, with orbits of 4.3, 9.6, and 20.4 days, respectively.
“The perturbations induced by the planets are really tiny — the mass of the smallest planets is one hundred thousand times smaller than that of the star,” making the discoveries a triumph of telescope technology, says co-author Francois Bouchy of France’s Institut d’Astrophysique de Paris.
The team is led by Geneva Observatory’s Michel Mayor, who was part of the team that reported the first extrasolar planet finds in the 1990s. “Clearly these planets are only the tip of the iceberg,” Mayor said. “The analysis of all the stars studied with HARPS shows that about one-third of all solar-like stars have either super-Earth or Neptune-like planets with orbital periods shorter than 50 days.”
Mayor says his team currently has 45 candidate planets that fit the bill.
» More information about extrasolar planets
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