rfmcdonald | [LINK] On exoplanet Gliese 163c (Reply)

io9's George Dvorsky alerted me to the discovery of a broadly Earth-like planet orbiting a relatively nearby star.

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."

The most noteworthy thing about Gliese 163, a red dwarf star visible only from Earth's Southern Hemisphere and then only with a telescope, is that it's in the same general neighbourhood as Zeta Reticulii, famous to UFO watchers as the star supporting the homeworld(s) of the Grey aliens. (No signs of life on Gliese 163, of course!)

A press release from the aforementioned Planetary Habitability Laboratory goes into more detail about the Gliese 163 system and the habitability of worlds orbiting red dwarf stars more generally.

A new superterran exoplanet (aka Super-Earth) was found in the stellar habitable zone of the red dwarf star Gliese 163 by the European HARPS team. The planet, Gliese 163c, has a minimum mass of 6.9 Earth masses and takes nearly 26 days to orbit its star. Superterrans are those exoplanets between two and ten Earth masses, which are more likely composed of rock and water. Gliese 163 is a nearby red dwarf star 50 light years away in the Dorado constellation. Another larger planet, Gliese 163b, was also found to orbit the star much closer with a nine days period. An additional third, but unconfirmed planet, might be orbiting the star much farther away.

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The potential for habitable planets around red dwarf stars has been and issue of much debate. Tidal effects on the planets around these stars might cause extra surface heating or even tidal locking (always giving the same face to its parent star). Also, these stars are more active and their stellar wind might erode planetary atmospheres much faster. These factors might preclude the potential for life on smaller planets but not for planets with thicker atmospheres, something expected for superterran planets. Our Solar System lacks an example of a superterran. Its eight planets are either the smaller terrestrial kind, like Earth, or the larger gas giants, like Jupiter. Understanding superterrans around red dwarf stars, a non Sun-like star, just adds to the challenge of assessing their habitability.