Fifty new exoplanets discovered
An international team of astronomers including LATMOS and IAP (1) in France, has today announced the discovery of 50 new extrasolar planets in orbit around nearby stars. This impressive haul, collected by ESO's (2) Chile-based highly-performing exoplanet-searcher HARPS, includes 16 super-Earths, in other words planets whose mass is comprised between one and ten times that of the Earth. One of these super-Earths is located within the habitable zone of its star: it could therefore support life. In addition, researchers have determined that over 40% of stars similar to the Sun host at least one planet whose mass is inferior to that of Saturn. These results were presented on 12 September at a conference on Extreme Solar Systems held in Wyoming, USA.
Since 2003, HARPS has been surveying the skies in search for planets orbiting stars other than the Sun. This spectrograph, which is installed on ESO's telescope at La Silla Observatory in Chile, was partly developed in France. It is the world's best-performing instrument of its kind: it had previously detected around one hundred exoplanets (2) using a highly-precise technique based on the measurement of stars'(3) radial velocity. Fifty new planets now add to these findings. They include an impressive number of super-Earths (4) (16 in total) and planets similar to Neptune (5) orbiting stars very similar to our Sun.
Using HARPS observations, astronomers have significantly improved their estimation of the likelihood for a low-mass planet (as opposed to a gaseous giant such as Jupiter or Saturn) to orbit a star similar to the Sun. They have come to the conclusion that over 40% of these stars host at least one planet whose mass is smaller than that of Saturn (i.e. comprised beteen 3 and 100 times the mass of the Earth).
HARPS should reach unprecedented levels of stability and sensitivity over the next few years, which should help it to detect rocky planets that could support life. Ten nearby stars similar to the Sun (6) have been selected for new systematic research of super-Earths. It took astronomers two years to discover five planets with a mass five times lower than that of the Earth. One of these could support life. So far, HARPS has detected two super-Earths within habitable zones (narrow zones surrounding a star, inside which water can be present in liquid form). The first one, Gliese 581 d, was discovered in 2007. The second, named HD 85512 b, has an estimated mass of around 3.6 times that of the Earth. Located 36 light-years away, it is the planet with the lowest mass ever detected by HARPS. "The detection of HD 85512 b shows that other super-Earths may be discovered in the habitable zones of stars similar to the Sun," points out Michel Mayor, who launched the HARPS project, now led by his colleague Stéphane Udry of the Geneva Observatory.
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Vue d'artiste de l'une des 50 nouvelles exoplanètes découvertes par HARPS, la super-Terre rocheuse HD 85512b
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M. Kornmesser/ ESO
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The first list of habitable planets near the solar system should be published within the next 20 years. It should make it possible to detect potential spectroscopic signatures of life in exoplanet atmospheres. These results strengthen astronomers' opinion that they will soon discover new small rocky planets around stars similar to our Sun. New instruments should help to take this research further, including: the SOPHIE spectrograph at the Haute Provence Observatory; a copy of HARPS to be installed on the Italian telescope Galilelo in the Canary Islands tp study the stars in the northern hemisphere; and finally a new and more powerfur planet searcher called ESPRESSO, which is due to be set up in 2016 on ESO's Very Large Telescope (VLT) in Chile.
The HARPS consortium is composed by Michel Mayor (Observatoire de Genève [OAUG], Switzerland), M. Marmier (OAUG), C. Lovis (OAUG), S. Udry (OAUG), D. Ségransan (OAUG), F. Pepe (OAUG), W. Benz (Physikalisches Institut Universität Bern, Switzerland), Jean-Loup Bertaux (LATMOS / IPSL, France), François Bouchy (IAP and Observatoire de Haute-Provence, France), X. Dumusque (OAUG), G. LoCurto (ESO, Germany), C. Mordasini (Max Planck Institute of Astronomy, Germany), D. Queloz (OAUG), N. C. Santos (Centro de Astrofísica da Universidade do Porto, Portugal and Departamento de Física de Astronomia, Faculdade de Ciências da Universidade do Porto, Portugal).
Notes
(1) Institut d'Astrophysique de Paris
(2) European Southern Laboratory
(3) In addition to the exoplanets discovered by using radial velocity measurements, over 1200 exoplanet candidates have been found by NASA's Kepler mission. An alternative method is then used: it consists in detecting the decline in a star's luminous intensity when a planet passes in front of it (transit). The majority of planets discovered via the transit method are very far from the Solar System (roughly six times further away than the planets detected by HARPS).
(4) This technique enables astronomers to estimate a planet's minimum mass. HARPS ("High Accuracy Radial Velocity Planet Searcher") measures the radial velocity of a star with very high precision (of the order of 3.5 km/hour), thus making it possible to infer the presence of a planet.
(5) Planets with a mass comprised between one and ten times that of the Earth are called super-Earths. Such planets do not exist in our Solar System but seem to be very common around other stars. Their discovery is extremely exciting as they could support a form of life, in the hypothesis that they are rocky planets with water resources.
(6) Their mass is around 17 times that of the Earth.
(7) These stars have already been observed by HARPS and are known as allowing extremely precise radial velocity measurements.
Contact
Jean-Loup BERTAUX , LATMOS