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Record three super-Earths found in star's habitable zone

Paul Sutherland, Feature writer
Jun 26, 2013, 7:00 UTC

Sen—Astronomers have identified a star with at least six planets in orbit of which three are potentially habitable. And if there are aliens on any of these super-Earth worlds, they will be able to marvel at the presence of not one but three suns in their sky.

That is because the star with the planets, labelled Gliese 667C, is part of a triple-star system in orbit around each other. They lie at the cosmically close distance of just 22 light-years which makes them relatively easy to study.

The three stars (the other two are called, you guessed it, Gliese 667A and Gliese 667B) can be found in the constellation of Scorpius.

Gliese 667C was already known to have three planets in orbit, with one of them being more massive than Earth but not as big as a gas giant, in the star’s so-called habitable zone. Now new observations with the 3.6-metre telescope at the European Southern Observatory’s La Silla site in Chile have found three more.

They were detected using an instrument fitted to the telescope called the High Accuracy Radial velocity Planet Searcher (HARPS). What has excited astronomers is that two of the new finds are also in the habitable zone, and are also super-Earths. The presence of three planets in this vital region around one star is a record find.

Because water could exist as a liquid on all three of the planets, and they might well be rocky, it means that any of them could be suitable for the presence of life such as we know it. The third of the new finds lies outside the zone. The evidence suggests there might be a seventh planet in the system too.

The team of astronomers who made the new disocovery were led by Guillem Anglada-Escudé of the University of Göttingen, Germany, and Mikko Tuomi of the University of Hertfordshire, in the UK.

Gliese 667C planets

Relative positions of the planets orbiting Gliese 667C. Credit: ESO

They had another look at Gliese 667C by combining HARPS observations with data from ESO’s Very Large Telescope, also in Chile, the Keck 10-metre telescope on Hawaii and the 6.5-metre Magellan II Telescope at the Las Campanas Observatory in Chile.

Dr Tuomi said: “We knew that the star had three planets from previous studies, so we wanted to see whether there were any more. By adding some new observations and revisiting existing data we were able to confirm these three and confidently reveal several more. Finding three low-mass planets in the star’s habitable zone is very exciting!”

Co-discoverer Rory Barnes, of the University of Washington, USA, said: “The number of potentially habitable planets in our galaxy is much greater if we can expect to find several of them around each low-mass star — instead of looking at ten stars to look for a single potentially habitable planet, we now know we can look at just one star and find several of them.”

NASA’s Kepler Space Telescope has shown that Sun-like stars with planets are plentiful in our Milky Way galaxy. The new discoveries show that cooler, dimmer stars like Gliese 667C can host systems of planets too.

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An artist's impression of the orbits of the planets around Gliese 667C. Credit: Rory Barnes/ESO