28 March 2012

from Telegraph Website

Hundreds of thousands of stars crowded

into the swirling core of our spiral Milky Way galaxy

Photo: NASA
 

Researchers discovered that at least 100 of the ''super-Earths'' may be on our galactic doorstep, at distances of less than 30 light years, or about 180 trillion miles, from the sun.

Astronomers say the findings were made after conducting a survey of red dwarf stars, which account for about four in five stars in the Milky Way.

They calculate that around 40 per cent of red dwarfs have a rocky planet not much bigger than Earth orbiting the ''habitable zone'', in which liquid surface water can exist.

Scientists say that where there is water, there also could be life although they add that being in the habitable zone is no guarantee that life has evolved on a planet.

Dr Xavier Bonfils, from Grenoble University in France, who led the international 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.''

In their study, the team of astronomers surveyed a carefully chosen sample of 102 red dwarfs using the European Southern Observatory's 3.6-metre telescope at La Silla, Chile.

A total of nine super-Earths - planets with masses between one and 10 times that of Earth - were found. Two were located within the habitable zones of the stars Gliese 581 and Gliese 667 C.

These data were combined with other observations, including those of stars which did not have planets.

The astronomers, whose research was reported in the journal Astronomy & Astrophysics, worked out that habitable zone super-Earths orbiting red dwarfs occurred with a frequency of around 41 per cent.

Meanwhile massive planets similar to Jupiter and Saturn were rare around red dwarfs. Less than 12 per cent of the stars were expected to have such ''gas giants''.

Because red dwarf are common near the sun, many ''super-Earths'' may not be far away in astronomical terms. The scientists estimate there could be around 100 habitable zone planets within 30 light years.

Red dwarfs are cooler than the sun, which means planets must orbit close to their parent stars to be warm enough to be habitable. Scientists said this might not be good news for life.

Dr Stephane Udry, from Geneva Observatory, who is also a member of the international team, added:

"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.

''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.''

One light year is nearly six trillion miles.