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HARPS discovers 32
new exoplanets

Posted: October 19, 2009

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At an international exoplanet conference held in Porto today, HARPS (High Accuracy Radial Velocity Planet Searcher) scientists announce a hand of 32 new exoplanets, boosting the count to over 400.

The new additions cover the complete spectrum of exoplanets uncovered by previous searches, from "typical" hot jupiters, super-Neptunes and super-Earths, to planets found around low mass and low metallicity stars and in multiple planet systems.

One of the new discoveries announced today orbits the star Gliese 667 C, which belongs to a triple system. The six Earth-mass exoplanet circulates around its low-mass host star at a distance equal to 0.05AU. The host star is a companion to two other low-mass stars, which are seen in the distance of this artist's impression. Image: ESO/L. Cal¨ada.

"HARPS is a unique, extremely high precision instrument that is ideal for discovering alien worlds," says Stéphane Udry, who made the announcement. “We have now completed our initial five-year programme, which has succeeded well beyond our expectations.”

The HARPS instrument is the spectrograph for ESO's 3.6 metre telecope at the La Silla observatory in Chile and detects exoplanets by monitoring small changes in the star's radial velocity as it wobbles from the tug of an orbiting planet. During the first five years of operations the team utilised 530 nights for observing, and to date have discovered the first super-Earth, a trio of Neptune-type planets, the first super-Earth in the habitable zone of a small star, and the lightest exoplanet.

One aspect of the HARPS planet-hunting program focused on the search for planets around low mass dwarf stars, or stars with a lower metal content than our Sun, so-called M-dwarfs. These stars are thought to be less favourable for the formation of planets, which form in the metal-rich disc around the young star. However, the team found three candidate exoplanets of up to four Jupiter masses around stars that are metal-deficient, demonstrating that planets can indeed form around low metal stars.

“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 team member Xavier Bonfils.

The new findings also include two six-Earth mass planet candidates orbiting their low mass M-dwarf hosts in seven day periods, a 0.47 Jupiter mass planet orbiting with a fifty seven day period and a four Jupiter mass planet orbiting in one thousand days. The results also suggest that some 40-60 percent of Sun-like stars could host low mass planets.

Although the first phase of the observing programme is now officially complete, HARPS has secured its place as one of the world's top exoplanet hunters and will push on towards the detection of more Earth-type planets in the coming years.

This discovery was announced today during the ESO/CAUP conference “Towards Other Earths: perspectives and limitations in the Extremely Large Telescope era", taking place in Porto, Portugal all this week.

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