Probably about one hundred in the vicinity of the Solar System

Rocky planets not much larger than Earth are very common in the habitable zones around stars red weak. The international team believes that there must be tens of billions of such planets in our galaxy, the Milky Way, and probably about one hundred in the vicinity of the Solar System. This is the first time directly measured the frequency of super-Earths around red dwarfs, which account for 80% of the stars of the Milky Way. An international team just to make this the first direct estimate of the number of light planets around red dwarf stars. To do this, have used observations made with the HARPS spectrograph installed at the 3.6-meter telescope at ESO (La Silla Observatory in Chile).

 A recent announcement by demonstrating that in our galaxy have planets everywhere, used a different method was not sensitive to this important type of explants.

The HARPS team has been looking for explants orbiting the most common stars in the Milky Way - red dwarf stars (also known as M-type dwarfs). These stars are faint and cold compared to our Sun, but very common and long-lived, and in fact account for 80% of all stars of the Milky Way. 

"Our new observations with HARPS imply that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone, an area that allows the existence of liquid water on the surface of the planet," said Xavier Bonfils (IPAG, Sciences of the Universe Observatory of Grenoble, France), who leads the team. "Because red dwarfs are so common, there are about 160 billion in the Milky Way, this leads to the conclusion that there are tens of billions of planets of this type only in our galaxy." 

The HARPS team did a survey over a period of six years of a carefully selected sample in the southern sky made up of 102 red dwarf stars. We found a total of nine super-Earths (planets with masses between one and ten times the mass of Earth), including two in the habitable zone of Gliese 581 and Gliese 667 C respectively. Astronomers were able to estimate its weight and the distance to the host star around which orbited. 

Combining all data (including observations of stars had no planets) and examining the fraction of planets exist that could be discovered, the team has been able to deduce how common they may be different types of planets around red dwarfs. They found that the frequency of the presence of super-Earths in the habitable zone is 41% ranging from 28% to 95%. 

On the other hand, more massive planets similar to Jupiter and Saturn in our solar system seem to be very common around red dwarfs. It is believed that less than 12% of red dwarfs have giant planets (with masses between 100 and 1,000 times the mass of Earth). 

Given the many red dwarf stars near the Sun, the new estimate implies that, probably in the vicinity of the solar system at distances less than 30 light years, there may be around one hundred super-Earths in the habitable zones of these stars. 

"The habitable zone around a red dwarf, where the temperature is suitable for liquid water on the surface is closer to the star than in the case of Earth from the Sun," says Stéphane Udry ( Geneva Observatory researcher and team member). "But red dwarfs are known to be subject to eruptions or stellar flares, which would flood the planet X-ray or ultraviolet radiation: it would make more difficult the existence of life." 

One of the planets discovered in the survey of red dwarf Gliese 667 HARPS is Cc. It is the second planet from the triple star system and appears to be located near the center of the habitable zone. Although this planet is more than four times heavier than Earth, is the closest to our planet from those found so far, and almost certainly has the right conditions for the existence of liquid water on its surface. This is the second super-Earth in the habitable zone of a red dwarf discovered during the survey of HARPS, following the announcement of the discovery of Gliese 581 d in 2007 and its subsequent confirmation in 2009. 

"Now we know there are many super-Earths around red dwarfs close, we need to identify more using both HARPS and other future instruments. It is expected that some of these planets pass in front of its parent star during its orbit around it - this will open the exciting possibility of studying the atmosphere of these planets and signs of life, "he says Xavier Delfosse, one of the members of team.