March 28, 2012
Earth-Like Planets Very Common In Red Dwarf Systems
The astronomers from that European Space Observatory have helped reveal that rocky planets not much bigger than Earth are very common in the habitable zone around faint red stars.
A team of astronomers estimates there are tens of billions of these rocky planets in the Milky Way galaxy alone, and about one hundred in the Sun's neighborhood.
The team used observations with the HARPS spectrograph on the telescope at ESO's La Silla Observatory in Chile.
They had been searching for exoplanets orbiting red dwarfs, which are the most common types of stars in the Milky Way.
Red dwarfs are faint and cool compared to the Sun, but are very common and long-lived, accounting for 80 percent of the stars in the Milky Way.
“Our new observations with HARPS mean that about 40% 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 team, said in a press release. “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.”
The astronomers surveyed a sample of 102 red dwarf stars in the southern skies over a six-year period. They found nine super-Earths, including two inside the habitable zones of Gliese 581 and Gliese 667 C.
The team was able to work out how common different sorts of planets are around red dwarfs, finding that the chances of a super-Earth planet in the habitable zone is 41 percent.
They also found that giant gas planets like Jupiter and Saturn are more rare around red dwarf's, with only about 12 percent of the stars having these types of planets.
The astronomers have determined that there are about 100 super-Earth planets in the habitable zones around stars in the same neighborhood of the Sun, less than 30 light-years away.
"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," StÃ©phane Udry, of Geneva Observatory and a member of the team, said in a press release. "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."
During the survey, the team found the closest twin to Earth so far, hosting the right conditions for the existence of liquid water on its surface.
Gliese 667 Cc is the second planet in its triple star system and lies close to the center of the habitable zone.
“Now that we know that there are many super-Earths around nearby red dwarfs we need to identify more of them using both HARPS and future instruments. Some of these planets are expected to pass in front of their parent star as they orbit – this will open up the exciting possibility of studying the planet´s atmosphere and searching for signs of life,” Xavier Delfosse, another member of the team, said in a press release.
Image Caption: This artist´s impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. The other two more distant stars, Gliese 667 A and B appear in the sky also to the right. Astronomers have estimated that there are tens of billions of such rocky worlds orbiting faint red dwarf stars in the Milky Way alone. Credit: ESO/L. CalÃ§ada