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September 12, 2011

Fifty New Exoplanets Discovered by HARPS

Astronomers using ESO’s world-leading exoplanet hunter HARPS have today announced a rich haul of more than 50 new exoplanets,including 16 super-Earths, one of which orbits at the edge of the habitable zone of its star. By studying the properties of all the HARPS planets found so far, the team has found that about 40% of stars similar to the Sun have at least one planet lighter than Saturn.

The HARPS spectrograph on the 3.6-metre telescope at ESO’s La Silla Observatory in Chile is the world’s most successful planet finder. The HARPS team, led by Michel Mayor (University of Geneva, Switzerland), today announced the discovery of more than 50 new exoplanets orbiting nearby stars, including sixteen super-Earths. This is the largest number of such planets ever announced at one time. The new findings are being presented at a conference on Extreme Solar Systems where 350 exoplanet experts are meeting in Wyoming, USA.


HARPS is the ESO facility for the measurement of radial velocities with the highest accuracy currently available. It is fibre-fed by the Cassegrain focus of the 3.6m telescope in La Silla. The instrument is built to obtain very high long term radial velocity accuracy (on the order of 1 m/s). To achieve this goal, HARPS is designed as an echelle spectrograph fed by a pair of fibres and optimised for mechanical stability. It is contained in a vacuum vessel to avoid spectral drift due to temperature and air pressure variations. One of the two fibres collects the star light, while the second is used to either record simultaneously a Th-Ar reference spectrum or the background sky


Evening view of La Silla at the moment of "telescope start-up". The dome of the Swiss 1.2-m Leonhard Euler Telescope and the adjacent building are seen in the foreground, immediately to the right of the ramp leading to the ESO 3.6-m New Technology Telescope (NTT) in its octogonal enclosure. Credit: ESO/H.Zodet



“The harvest of discoveries from HARPS has exceeded all expectations and includes an exceptionally rich population of super-Earths and Neptune-type planets hosted by stars very similar to our Sun. And even better — the new results show that the pace of discovery is accelerating,” says Mayor.

In the eight years since it started surveying stars like the Sun using the radial velocity technique HARPS has been used to discover more than 150 new planets. About two thirds of all the known exoplanets with masses less than that of Neptune were discovered by HARPS. These exceptional results are the fruit of several hundred nights of HARPS observations.

Working with HARPS observations of 376 Sun-like stars, astronomers have now also much improved the estimate of how likely it is that a star like the Sun is host to low-mass planets (as opposed to gaseous giants). They find that about 40% of such stars have at least one planet less massive than Saturn. The majority of exoplanets of Neptune mass or less appear to be in systems with multiple planets.

With upgrades to both hardware and software systems in progress, HARPS is being pushed to the next level of stability and sensitivity to search for rocky planets that could support life. Ten nearby stars similar to the Sun were selected for a new survey. These stars had already been observed by HARPS and are known to be suitable for extremely precise radial velocity measurements. After two years of work, the team of astronomers has discovered five new planets with masses less than five times that of Earth.

These results make astronomers confident that they are close to discovering other small rocky habitable planets around stars similar to our Sun. New instruments are planned to further this search. These include a copy of HARPS to be installed on the Telescopio Nazionale Galileo in the Canary Islands, to survey stars in the northern sky, as well as a new and more powerful planet-finder, called ESPRESSO, to be installed on ESO’s Very Large Telescope in 2016.

Currently the number of exoplanets stands at close to 600. In addition to exoplanets found using radial velocity techniques, more than 1200 exoplanet candidates have been found by NASA’s Kepler mission using an alternative method — searching for the slight drop in the brightness of a star as a planet passes in front of it (transits) and blocks some of the light. The majority of planets discovered by this transit method are very distant from us. But, in contrast, the planets found by HARPS are around stars close to the Sun. This makes them better targets for many kinds of additional follow-up observations.

The HARPS search for Earth-like planets in the habitable zone (18 pages)

The HARPS search for southern extra-solar planets (24b pages)

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