Astronomers Re-examine Gliese 667C, Suggest First System with Fully Packed Habitable Zone

Jun 25, 2013 by Sci-News.com

An international team of researchers has used new observations of Gliese 667C to find evidence of up to seven planets circling the star, including three super-Earths that orbit in the habitable zone.

This image shows Gliese 667Cb, a super-Earth that orbits the star Gliese 667C. Stars Gliese 667A and Gliese 667B are seen here in the distance (ESO / L. Calçada)

This image shows Gliese 667Cb, a super-Earth that orbits the star Gliese 667C. Stars Gliese 667A and Gliese 667B are seen here in the distance (ESO / L. Calçada)

Gliese 667C is part of a triple star system known as Gliese 667. Located in the constellation of Scorpius only 22 light-years away, the star is just over one third of the mass of the Sun.

Previous studies had found that it hosts three planets – Gliese 667 Cb, Gliese 667 Cc and Gliese 667 Cd, including one in the habitable zone.

This is the view from the exoplanet Gliese 667Cd looking towards the planet’s parent star Gliese 667C (ESO / M. Kornmesser)

This is the view from the exoplanet Gliese 667Cd looking towards the planet’s parent star Gliese 667C (ESO / M. Kornmesser)

Now, the team led by Dr Guillem Anglada-Escudé of the University of Göttingen re-examined the system, and found evidence of seven planets around Gliese 667C.

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.

This image shows planets in the Gliese 667C system (ESO)

This image shows planets in the Gliese 667C system (ESO)

“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!” said Dr Mikko Tuomi of the University of Hertfordshire, UK, second author of the paper reporting the discovery in the journal Astronomy & Astrophysics (paper in .pdf).

“Three of these planets are confirmed to be super-Earths that are within the habitable zone.”

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

“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,” said study co-author Dr Rory Barnes from the University of Washington.

Gliese 667C’s habitable zone lies entirely within an orbit the size of Mercury’s, much closer in than for our Sun. The system is the first example of a system where such a low-mass star is seen to host several potentially rocky planets in the habitable zone.

This image shows the sky around the triple star Gliese 667. The bright star at the center is Gliese 667 A and B, the two main components of the system, which cannot be separated in this image. Gliese 667C is visible as a bright star, very close and just under A and B, still in the glare of these brighter stars. At the upper-left NGC 6357 is visible and towards the bottom of the picture NGC 6334 - the Cat’s Paw Nebula (ESO)

This image shows the sky around the triple star Gliese 667. The bright star at the center is Gliese 667 A and B, the two main components of the system, which cannot be separated in this image. Gliese 667C is visible as a bright star, very close and just under A and B, still in the glare of these brighter stars. At the upper-left NGC 6357 is visible and towards the bottom of the picture NGC 6334 – the Cat’s Paw Nebula (ESO)

“These new results highlight how valuable it can be to re-analyze data in this way and combine results from different teams on different telescopes,” Dr Anglada-Escudé concluded.

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Bibliographic information: G. Anglada-Escudé et al. 2013. A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone. Astronomy & Astrophysics, in press; doi: 10.1051/0004-6361/201321331