28 March 2012
Billions of potentially
habitable planets may exist within our galaxy, the Milky
Way, raising new prospects that life could exist near
Earth, a study has found.
Hundreds of thousands of stars crowded
into the swirling
core of our spiral Milky Way galaxy
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
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,
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
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