December 5, 2005
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| Digitized Sky Survey image of the star Gliese 581 |
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(PLANETQUEST) -- European astronomers have announced the discovery of two new extrasolar planets, including a giant and one of the smallest ever found. The new discoveries bring the total number of known extrasolar planets to 157.
A planet roughly 17 times the Earth's mass, or about the mass of Neptune, was detected orbiting the star Gliese 581, which belongs to a class of stars known as red dwarfs. These stars are at least 50 times fainter than the sun and are the most common stars in our galaxy. Among the 100 closest stars to the sun, 80 are red dwarfs.
"Our finding possibly means that planets are rather frequent around the smallest stars," said Xavier Delfosse of the Laboratoire d'Astrophysique de Grenoble (France), co-author of the paper relating the work. "It certainly tells us that red dwarfs are ideal targets for the search for (extrasolar planets)." Delfosse was quoted in an ESO press release about the discovery.
The star is located 20.5 light-years away in the Libra constellation, and has a mass of about one third that of the sun. The planet, one of the smallest yet detected, orbits very close to the star and completes a full circle in only 5.4 days.
The discovery was made by a team of French and Swiss astronomers using the HARPS instrument on the European Southen Observatory's (ESO's) 3.6-m telescope at La Silla, Chile.
In a separate announcement, a European team reported the discovery of a massive companion to the young disc star HD 81040, located 106 light-years away, also in the constellation Libra. The planet is a gas giant, about seven times the mass of Jupiter, and takes more than 1,000 days to complete an orbit. The discovery was made by ELODIE Planet Search project, based at the Haute-Provence Observatory in France.
Both planets were detected indirectly using the radial velocity method, which infers the existence of an unseen planet from the wobble induced on the host star.
