Scientists have identified a new solar system with three potentially habitable Earth-like planets orbiting a nearby star, just 22 light-years away in the constellation Scorpius.

A closer look at the previously-studied star Gliese 667C revealed a treasure trove of planets with three super-Earths in the habitable zone around the star.

Astronomers combined new observations of Gliese 667C with existing data from HARPS at European Southern Observatory ESO’s 3.6-metre telescope in Chile, to reveal the system.

A record-breaking three of these planets are super-Earths lying in the zone around the star where liquid water could exist, making them possible candidates for the presence of life.

This is the first system found with a fully packed habitable zone.

Gliese 667C is a very well-studied star. Just over one third of the mass of the Sun, it is part of a triple star system known as Gliese 667 (GJ 667), 22 light-years away in the constellation of Scorpius (The Scorpion).

This is quite close to us – within the Sun’s neighbourhood – and much closer than the star systems investigated using telescopes such as the planet-hunting Kepler space telescope.

Previous studies of Gliese 667C had found that the star hosts three planets with one of them in the habitable zone.

Now, a team of astronomers led by Guillem Anglada-Escude of the University of Gottingen, Germany and Mikko Tuomi of the University of Hertfordshire, UK, has re-examined the system.

They added new HARPS observations, along with data from ESO’s Very Large Telescope, the WM Keck Observatory and the Magellan Telescopes, to the already existing picture. The team has found evidence for up to seven planets around the star.

These planets orbit the third fainter star of a triple star system. Viewed from one of these newly found planets the two other suns would look like a pair of very bright stars visible in the daytime and at night they would provide as much illumination as the full Moon.

The new planets completely fill up the habitable zone of Gliese 667C, as there are no more stable orbits in which a planet could exist at the right distance to it.

“We knew that the star had three planets from previous studies, so we wanted to see whether there were any more,” said Tuomi.

“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!” Tuomi said.

Three of these planets are confirmed to be super-Earths – planets more massive than Earth, but less massive than planets like Uranus or Neptune – that are within their star’s habitable zone, a thin shell around a star in which water may be present in liquid form if conditions are right.

This is the first time that three such planets have been spotted orbiting in this zone in the same system.

(This article was published on June 26, 2013)
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