Many billions of super-Earths may be orbiting red dwarfs in Milky Way

Washington, Mar 29 (ANI): Rocky planets not much bigger than Earth are ubiquitous in the habitable zones around faint red stars, according to a new research.

e international team estimates that there are tens of billions of such planets in the Milky Way galaxy alone, and probably about one hundred in the Sun's immediate neighbourhood.

This is the first direct measurement of the frequency of super-Earths around red dwarfs (the most common kind of star in the Milky Way -also known as M dwarfs), which account for 80 percent of the stars in the Milky Way.

This first direct estimate of the number of light planets around red dwarf stars has just been announced by an international team using observations with the HARPS spectrograph on the 3.6-meter telescope at ESO's La Silla Observatory in Chile.

A recent announcement showing that planets are ubiquitous in our galaxy used a different method that was not sensitive to this important class of exoplanets.

"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," said Xavier Bonfils (IPAG, Observatoire des Sciences de l'Univers de Grenoble, France), the leader of the team.

"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 HARPS team surveyed a carefully chosen sample of 102 red dwarf stars in the southern skies over a six-year period.

A total of nine super-Earths (planets with masses between one and ten times that of Earth) were found, including two inside the habitable zones of Gliese 581 and Gliese 667 C respectively.

The astronomers could estimate how heavy the planets were and how far from their stars they orbited.

By combining all the data, including observations of stars that did not have planets, and looking at the fraction of existing planets that could be discovered, the team has been able to work out how common different sorts of planets are around red dwarfs.

They find that the frequency of occurrence of super-Earths in the habitable zone is 41 percent with a range from 28 percent to 95 percent.

On the other hand, more massive planets, similar to Jupiter and Saturn in our Solar System, are found to be rare around red dwarfs. Less than 12 percent of red dwarfs are expected to have giant planets (with masses between 100 and 1000 times that of the Earth).

As there are many red dwarf stars close to the Sun the new estimate means that there are probably about one hundred super-Earth planets in the habitable zones around stars in the neighbourhood of the Sun at distances less than about 30 light-years.

"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," said Stephane Udry (Geneva Observatory and member of the 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," Udry added. (ANI)