Three super-earths have now been found orbiting a single star, Gliese 667C, in the constellation Scorpius, the Scorpion. These planets may have the capability of supporting life, and exist in the star's "habitable zone" where conditions could support liquid water. It is still unknown whether or not these super-Earths have rocky surfaces or atmospheres.
Since Gliese 667C is only about one-third the mass of the Sun, it is cooler and dimmer than our home star. Because of this, the habitable zone in which these planets reside is much closer to that star than it is in our solar system.
Gliese 667C is the dimmest member of a three-star system or trinary, named Gliese 667, and it lies 22 light years away from the Earth. Earlier studies had revealed three total planets, including one super-earth, in the trinary solar system. The newest research puts this number at between five and seven planets orbiting the nearby star. The new examination which shed light on the additional planets was a combination of new observations and re-examining information collected from earlier studies.
"We re-examined the existing data, added some new observations, and applied two different data analysis methods especially designed to deal with multi-planet signal detection. Both methods yielded the same answer: there are five very secure signals and up to seven low-mass planets in short-period orbits around the star," Guillem Anglada-Escude, from the University of Gottingen in Germany, who headed the study, said.
In addition to the three plus-sized Earth-like planets, astronomers have also now found a total of four other planets orbiting the star. Such low-mass stars, which make up the majority of the members of our galaxy, could prove to be among the easiest systems to identify new super-earths. Because their habitable zones are so close to a star, the planet's gravitational effects on its home sun are easier to measure than a more distant world.
"We knew that the star had three planets from previous studies, so we wanted to see whether there were any more. 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!" Mikko Tuomi of the University of Hertfordshire, said.
Super-earths are considered to be those planets with masses between one and 10 times that of our home world, or roughly larger than the Earth, but smaller than Neptune. It is unlikely that other super-earths exist in the habitable zone of Gliese 667C, as all the stable orbits in that range of distances are already occupied.
