HARPS is zooming in fast on the discovery of a Twin Earth: The latest batch of exoplanets announced yesterday comprises no less than 32 new discoveries. Including these new results, data from HARPS have led to the discovery of more than 75 exoplanets in 30 different planetary systems.
HARPS is the High Accuracy Radial velocity Planet Searcher at the ESO 3.6m telescope at La Silla in Chile"s Atacama Desert dedicated to the discovery of extrasolar planets. Due to its amazing precision, the search for small planets, those with a mass of a few times that of the Earth known as super-Earths and Neptune-like planets has been given a dramatic boost.
The HARPS consortium selected their target stars with extreme care, with several sub-programs aimed at looking for planets around solar-like stars, low-mass dwarf stars, or stars with a lower metal content than the Sun. The number of exoplanets known around low-mass stars so-called M dwarfs has also dramatically increased, including a handful of super Earths and a few giant planets challenging planetary formation theory
HARPS has facilitated the discovery of 24 of the 28 planets known with masses below 20 Earth masses. As with the previously detected super-Earths, most of the new low-mass candidates reside in multi-planet systems, with up to five planets per system.
In 1999, ESO launched a call for opportunities to build a high resolution, precise spectrograph for the ESO 3.6-metre telescope at La Silla, Chile. Michel Mayor, from the Geneva Observatory, led a consortium to build HARPS, which was installed in 2003 and was soon able to measure the back-and-forward motions of stars by detecting small changes in a star"s radial velocity as small as 3.5 km/hour, a steady walking pace. Such a precision is crucial for the discovery of exoplanets and the radial velocity method, which detects small changes in the radial velocity of a star as it wobbles slightly under the gentle gravitational pull from an (unseen) exoplanet, has been most effective method in the search for exoplanets.
In return for building the instrument, the HARPS consortium was granted 100 observing nights per year during a five-year period to carry out one of the most ambitious systematic searches for exoplanets so far implemented worldwide by repeatedly measuring the radial velocities of hundreds of stars that may harbour planetary systems.
The programme soon proved very successful. Using HARPS, Michael Mayor"s team discovered the first super-Earth (around Ara; ESO 22/04) in 2004; in 2006, the trio of Neptunes around HD 69830 (ESO 18/06); in 2007, Gliese 581d, the first super Earth in the habitable zone of a small star (ESO 22/07); and in 2009, the lightest exoplanet so far detected around a normal star, Gliese 581e (ESO 15/09). More recently, they found a potentially lava-covered world, with density similar to that of the Earth"s (ESO 33/09).
"These observations have given astronomers a great insight into the diversity of planetary systems and help us understand how they can form," says team member Nuno Santos.
"By targeting M dwarfs and harnessing the precision of HARPS we have been able to search for exoplanets in the mass and temperature regime of super-Earths, some even close to or inside the habitable zone around the star," says co-author Xavier Bonfils.
Casey Kazan
Image Credit: http://www.theogijzen.nl/images/earths%20twin.jpg
Source: ESO materials
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