Cool, Low Mass Stars Show Promise as Source of Habitable Planets


The star Gliese 667C, a mere 22 light years away, is offering some surprises when it comes to searching for alien planets potentially suited for life.

Thanks to new observations and a re-examination of previously existing radial velocity data, a multi-national team of astronomers concludes this low mass star hosts five to seven planets.


A record three to five of the planets are classified as "super Earths," which means they are larger than Earth but with no more girth than Neptune or Uranus. And they orbit in or on the border of Gliese 667C's habitable zone, a realm not too close nor too far from a host star, where temperatures allow water, if present, to exist in liquid form.

The findings suggest that other cooler, low mass stars may be promising targets for Earth-like planets that orbit close to their suns as well.

The study led by Guillem Anglada-Escudé, of the University of Göttingen, and including pioneering exo-planet hunter Paul Butler, of the Carnegie Institution for Science, as a collaborator notes that 80 percent of the stars in the Milky Way galaxy fall into this lower mass bracket -- reason for even more optimism.

Previous observations suggested Gliese 667C was home to three planets, with just one of them in the habitable zone.

"Instead of observing 10 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 University of Washington astronomer Rory Barnes, another collaborator. The study entitled, “A Dynamically-packed Planetary System Around GJ 667C With Three Super-Earths in its Habitable Zone," appears in the June 20 edition of the journal Astronomy & Astrophysics.

Gliese 667C is part of a triple star system. The stellar trio resides in the constellation Scorpius. In daytime as well as at night on each of the planets, these stars would provide the same illumination as the full moon on Earth. The latest studies suggest the super Earths have rocky surfaces.

Currently hobbled by reaction wheel failures, NASA’s Kepler space telescope was not a direct contributor to the study.

Anglada-Escudé's team developed the findings by reaching back a decade to sort through findings from the High Accuracy Radial velocity Planet Searcher (HARPS) at the European Southern Observatory's 3.6-metre telescope in Chile; the Carnegie Planet Finder Spectrograph (PFS) at the 6.5-metre Magellan II Telescope at the Las Campanas Observatory in Chile; and the HIRES spectrograph mounted on the Keck 10-metre telescope on Mauna Kea, Hawaii. Spectra taken using the UVES spectrograph on ESO's Very Large Telescope in Chile were used to fine tune the properties of Gliese 667C, according to announcements from the various observatories.

"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," said Anglada-Escudé in a statement.

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