An intriguing star system
Another super-Earth that orbits much closer to GJ 667C was previously detected in 2010, but the finding was never published, Vogt added. This planet, called GJ 667Cb, takes 7.2 days to circle the star but its location makes it far too hot to sustain liquid water on its surface.
"It's basically glowing cinders, or a well-lit charcoal," Vogt said. "We know about a lot of these, but they're thousands of degrees and not places where you could live."
But, the newly detected GJ 667Cc planet is a much more intriguing candidate, he said.
"When a planet gets bigger than about 10 times the size of the Earth, there's a runaway process that happens, where it begins to eat up all the gas and ice in the disk that it's forming out of and swells quickly into something like Uranus, Jupiter or Saturn," Vogt explained. "When you have a surface and the right temperature, if there's water around, there's a good chance that it could be in liquid form. This planet is right in that sweet spot in the habitable zone, so we've got the right temperature and the right mass range."
Preliminary observations also suggest that more planets could exist in this system, including a gas giant planet and another super-Earth that takes about 75 days to circle the star. More research will be needed to confirm these planetary candidates, as well as to glean additional details about the potentially habitable super-Earth, the scientists said.
Finding nearby alien planets
To make their discovery, the researchers used public data from the European Southern Observatory combined with observations from the W.M. Keck Observatory in Hawaii and the new Carnegie Planet Finder Spectrograph at the Magellan II Telescope in Chile.
Follow-up analyses were also made using a planet-hunting technique that measures the small dips, or wobbles, in a star's motion caused by the gravitational tug of a planet.
"With the advent of a new generation of instruments, researchers will be able to survey many M dwarf stars for similar planets and eventually look for spectroscopic signatures of life in one of these worlds," Anglada-Escudé said in a statement. Anglada-Escudé was with the Carnegie Institution for Science when he conducted the research, but has since moved on to the University of Gottingen in Germany.
With the GJ 667C system being relatively nearby, it also opens exciting possibilities for probing potentially habitable alien worlds in the future, Vogt said, which can't easily be done with the planets that are being found by NASA's prolific Kepler spacecraft.
"The planets coming out of Kepler are typically thousands of light-years away and we could never send a space probe out there," Vogt said. "We've been explicitly focusing on very nearby stars, because with today's technology, we could send a robotic probe out there, and within a few hundred years, it could be sending back picture postcards."
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