An artist's impression of a sunset seen from the super-Earth Gliese 667 Cc. Picture: AFP PHOTO / ESO / L. CALCADA
THERE are likely tens of billions of planets circling red dwarfs in our galaxy that may have the right conditions for sustaining life, according to a new estimate.
The finding, announced by European astronomers today, adds to the growing body of evidence that so-called super-Earths are ubiquitous in habitable zones of the cosmos.
Faint and cool compared to the Sun, red dwarfs account for 80 per cent of all the stars in the Milky Way. Using a planet-hunting instrument called the High Accuracy Radial velocity Planet Searcher (HARPS) in Chile, astronomers found other worlds orbiting two out of five of such stars.
"Our new observations with HARPS mean that about 40 per cent of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet," Xavier Bonfils, the leader of the European Southern Observatory team, said.
"Because red dwarfs are so common - there are about 160 billion of them in the Milky Way - this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone," he added.
Zachory Berta, a researcher with the Harvard-Smithsonian Center for Astrophysics who was not involved in the study, said the new finding agrees with recent observations from NASA's Kepler telescope, which has been detecting an increasing number of small planets around small stars.
"What makes me most excited about this result is what it means for our chances of detecting life on a planet other than Earth orbiting a star other than the Sun," Berta said in an email.
"The more habitable planets we find around nearby red dwarfs, the better our odds for truly being able to detect life on another world in our galaxy," he added.
But researchers involved in the study cautioned that red dwarfs themselves could create hostile conditions for the planets that orbit them.
"The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to the star than the Earth is to the Sun," Stephane Udry, a member of the European team.
"But red dwarfs are known to be subject to stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely."
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