Super-Earth wannabe may be habitable, if it exists

Joanna Carver, reporter

An artist's impression of the HD 40307 system, with HD 40307 g in the foreground
Image: J. Pinfield, for the RoPACS network at the University of Hertfordshire)

A new super-Earth wannabe may be poised to join the elite team of exoplanets that hold sway in the habitable zone, the region around a star where liquid water - and thus life - might exist.

The world is part of a possible planetary trio found after scientists sifted through old data on the orange star HD 40307. Sitting just 42 light years away, this quiet star was already known to host three super-Earths, but they are packed too close to the star to be habitable.

Using publicly available data from the High Accuracy Radial Velocity Planet Searcher (HARPS) in Chile, astronomers applied a new method for detecting signs of gravitational wobbles in starlight caused by orbiting planets. Their method filtered out similar signals caused by the star's own magnetic activity. The results pinpointed three more possible planets farther from the star, including one that seems to be comfortably in the habitable zone.

That world, dubbed HD 40307 g, is at least 7 times as massive as Earth and is unlikely to be tidally locked, meaning it doesn't show the same side to its star at all times, as the moon does to Earth. That means the planet has Earth-like days and nights, upping the chances of a life-friendly climate.

However, gravity wobbles only reveal a planet's mass. Astronomers would need to use other techniques to get its size and then calculate density. Without that information, it is anybody's guess what HD 40307 g is made of. The planet may be rocky like Earth, but it may also be a small gas giant, like a mini-Neptune, cautions study co-author Guillem Anglada-Escud? of the University of G?ttingen, Germany.

Other planet-hunting methods would also be able to confirm whether all three new super-Earths even exist.

"These signals are ... at the edge of detectability and some doubts remain(ed) on their planetary nature," Francesco Pepe of the Geneva Observatory in Switzerland, who also studied the original HARPS data, wrote in an email to the Los Angeles Times.

If the new super-Earths make the cut, they would add to a growing cadre of these middle-size planets found across the galaxy. "They seem to be pretty common," says Anglada-Escud?. "It is not clear if they represent the massive tip of the rocky planet population or the tail of the Neptune-like objects."

If most super-Earths are rocky, it's possible they are the cosmic norm, which would make our home planet more of a mini-Earth, he says.

Journal reference: arxiv.org/abs/1211.1617

Source: http://feeds.newscientist.com/c/749/f/10897/s/2563938a/l/0L0Snewscientist0N0Cblogs0Cshortsharpscience0C20A120C110Csuper0Eearth0Ewannabe0Emay0Ebe0Ehab0Bhtml0Dcmpid0FRSS0QNSNS0Q20A120EGLOBAL0Qonline0Enews/story01.htm

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