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Three Habitable Super-Earths Discovered In Multi-Planetary Star System

Astronomers have discovered a record-breaking planetary system with at least six planets orbiting its host star.

New observations of Gliese 667C show for the first time that three of these six new planet candidates are super-Earths. In order for a planet to qualify as a super-Earth, it must exist within the “habitable zone,” which is the zone around the star where liquid water could exist, making it a possible candidate to host life.

Gliese 667C is just one-third the mass of the Sun and is part of a star system known as Gliese 667. The star sits 22 light-years away from Earth in the constellation Scorpius. Astronomers have seen before that Gliese 667C hosted three planets, with one of them in the habitable zone, but the latest observation shows the count is much higher than that.

If you were to stand on the surface of one of these newly found planets, two other suns would look like a pair of very bright stars visible in the daytime. At night, the nearby stars are so close they would be providing as much illumination as the full moon.

This new discovery means the habitable zone around Gliese 667C is completely full, leaving no more room for another planet to exist.

“We knew that the star had three planets from previous studies, so we wanted to see whether there were any more,” says Mikko Tuomi of the University of Hertfordshire, UK. “By adding some new observations and revisiting existing data we were able to confirm these three and confidently reveal several more. Finding three low-mass planets in the star’s habitable zone is very exciting!”

Super-Earths, as opposed to Earth-like, are planets that are more massive than Earth but still in the habitable zone.

“The number of potentially habitable planets in our galaxy is much greater if we can expect to find several of them around each low-mass star — instead of looking at ten 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 Rory Barnes from the University of Washington and co-author of the study published in Astronomy & Astrophysics.

The habitable zone around Gliese 667C sits entirely within an orbit the size of Mercury’s. In our system Mercury is incredibly hot, thus unable to host liquid water. However, Gliese 667C is smaller than our star, so the orbit for the habitable zone can sit closer in. Gliese 667C is the first example of a system where such a low-mass star can host several potentially rocky planets.

“This exciting result was largely made possible by the power of HARPS and its associated software and it also underlines the value of the ESO archive,” said the European Space Observatory (ESO) scientist responsible for HARPS, Gaspare Lo Curto. “It is very good to also see several independent research groups exploiting this unique instrument and achieving the ultimate precision.”




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