A team of astronomers have discovered a record-breaking number of three habitable planets orbiting around a single nearby star, making those three planets good candidates in the search for "alien life".
The star Gliese 667C is about one-third the mass of our Sun, 22 light-years away from planet Earth in the constellation of Scorpius, and is orbited by at least six and as many as seven planets, the international team of researchers and scientists found. The three orbiting planets in question are known as super-Earths — planets more massive than Earth, but less massive than others like Neptune or Uranus.
Two main factors push these three planets forward as main contenders in the elusive search for extraterrestrial life: the power of Gliese 667C and the distance between the star and the planets.
There are many compact solar systems around Sun-like stars in the Milky Way, but many of them do not contain habitable planets because their super-Earths' orbits are very close to the star, within the orbit of Mercury. The high temperatures of their orbits make those super-Earths inhospitable for human and/or alien life.
Gliese 667C, however, is smaller in mass and therefore cooler and dimmer than our Sun. Those temperature conditions allows for the three super-Earths to be in the so-called hospitable zone around the star — or the zone where liquid water can still exist.
The Gliese 667C system is the first example of a low-mass star solar system packed with several planets in hospitable conditions. This is also the first time that three hospitable planets have been observed orbiting around the same star. This may direct scientists and astronomers in the future to targeting low-mass stars in the search for alien life.
The significance of the low-mass star carries heavy implications. Around 80% of the stars in the Milky Way, and especially stars around us, fall in the low-mass distinction. If low-mass stars breed packed solar systems, then the amount of potentially habitable planets around us could be more numerous than previously imagined.
Gliese 667C is a part of a three-star system — the other two stars being Gliese 667A and Gliese 667B. This means that during daytime, the three habitable planets have three suns in their daytime skies, and full moon illumination every night.