An international team of scientists working at European HARPS have announced the discovery of a large rocky planet residing within the stellar habitable zone of the red dwarf star Gliese 163. That increases the number of known potentially habitable planets to six — the majority of which have been discovered in the past year.

To better understand the significance of the discovery, we contacted Abel Méndez, an Associate Professor of Physics and Astrobiology in the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo. Méndez told us that the detection of Earth-like worlds is pacing up — and that there's likely a lot more to come. "There are more observatories dedicated to these types of searches, "he told io9, "and many of them now have the required sensitivity to find these potentially habitable planets."

Considered a superterran, or "super-Earth", the exoplanet is being called Gliese 163c. Located at the reasonable distance of 50 light years from Earth in the Dorado constellation, it is no smaller than 6.9 Earth masses and requires only 26 days to orbit its star.


That said, the HARPS astronomers speculate that Gliese 163c might be significantly smaller, about 1.8 to 2.3 Earth radii — but that will depend on subsequent analyses to detect its composition, most notably its rock and water content. It also receives on average about 40% more light from its parent star than the Sun, making it considerably hotter than Earth.

Méndez and the rest of the team at HARPS aren't sure what the atmosphere is like, but they suspect that it's a scaled up version of Earth's — giving it a surface temperature around 60°C. Most organisms on Earth cannot withstand temperatures above 50°C, but we know of many forms of extremophilic microbial life forms can thrive at those temperatures or higher.


Gliese 163c is now the sixth potentially habitable planet catalogued by Méndez, a list that includes four that orbit a red dwarf (Gliese 581d, Gliese 667Cc, Gliese 581g, and now Gliese 163c), one around a K-Star (HD 85512), and one around a Sun-like star (Kepler-22b). Méndez told us that upwards of 40% of red dwarf stars may have habitable planets. "Gliese 163c is now part of this statistic," he said, "but there should be many more waiting to be discovered."

That said, Méndez believes it still qualifies as an important object of inquiry as far as astrobiology is concerned. "Gliese 163c ranks fifth in our current list of six potentially habitable exoplanets because it is nearly twice the size of Earth and its temperature is also higher," he told io9, "but it's still an object of interest for the search of biosignatures by future observatories."

Gliese 163c was discovered by the European HARPS team led by Xavier Bonfils from the UJF-Grenoble/CNRS-INSU, Institut de Planétologie et d'Astrophysique of Grenoble, France. The paper is not yet available online, but the authors say it'll be available to the general public in about two weeks. The title of the paper is "The HARPS search for southern extra-solar planets⋆ XXXX. A planetary system around the nearby M dwarf GJ 163, with a super-Earth in the habitable zone." It was submitted to the journal Astronomy & Astrophysics.

We will update this page once the paper has been posted online.

All images via PHL @ UPR Arecibo.