by David Derbyshire
30 September 2010
Astronomers Discover Planet
20 Light Years Away With Similar Atmosphere
Gravity Which Has
'100% Chance of Life' - And May
Planet's gravity means a
human could walk on the surface
temperature is -12°C - cold but survivable
incredible discovery points to universe full of
The chances that future generations will
one day colonize the stars have just got higher.
Astronomers tonight announced the discovery of the most Earth-like
planet ever found - a rocky world three times the size of our own
world, orbiting a star 20 light years away.
The planet lies in the star's 'Goldilocks zone' - the region in
space where conditions are neither too hot or too cold for liquid
water to form oceans, lakes and rivers.
conception shows the inner four planets of
the Gliese 581 system
and their host star,
a red dwarf star only
20 light years away from Earth.
The four tiny planets
in the background are the planets that have already been discovered.
The closer, blue and
green planet is 581G, the most Earth-like planet ever discovered
The planet also appears to have an
atmosphere, a gravity like our own and could well be capable of
The discovery comes three years after astronomers found a similar,
slightly less habitable planet around the same star - described by
astronomers as being 'in our backyard' in the Milky Way.
Researchers say the findings suggest the universe is teeming with
world like our own.
'If these are rare, we shouldn't
have found one so quickly and so nearby,' Dr Steven Vogt who led
the study at the University of California, Santa Cruz.
'The number of systems with potentially habitable planets is
probably on the order of 10 or 20 per cent, and when you
multiply that by the hundreds of billions of stars in the Milky
Way, that's a large number.
There could be tens of billions of
these systems in our galaxy.'
GLIESE 581-g - FACT FILE
Diameter: 1.2 to 1.4
times that of the Earth
Mass: 3.1 and 4.3 times that of the Earth
Average surface temperature: between -24F and 10F
(-31C and -12C)
Distance from the Earth: 20 light years or
Time needed to travel to Gliese 581-g in a rocket
travelling one tenth the speed of light, or 19,000 miles
per second: 200 years
One of six planets to orbit the star Gliese 581
Length of year: 37 Earth days
Gravity: similar or slightly higher than Earth
Distance from its sun: around six million miles
The planet orbits a red dwarf which is 50 times cooler
and a third the size of our Sun
Composition: rocky with liquid water and
He told Discovery News:
'Personally, given the ubiquity and
propensity of life to flourish wherever it can, I would say that
the chances for life on this planet are 100 percent. I have
almost no doubt about it'.
The planet is so far away, spaceships
travelling close to the speed of light would take 20 years to make
the journey. If a rocket was one day able to travel at a tenth of
the speed of light, it would take 200 years to make the journey.
Planets orbiting distant stars are too small to be seen by
telescopes. Instead, astronomers look for tell-tale gravitational
wobbles in the stars that show a planet is in orbit.
The findings come from 11 years of observations at the W.M. Keck
Observatory in Hawaii.
The planet orbits a small red star called
Gliese 581 in the
constellation of Libra. The planet, named Gliese-g, is
118,000,000,000,000 miles away - so far away that light from its
start takes 20 years to reach the Earth.
It takes just 37 days to orbit its sun which means its seasons last
for just a few days. One side of the planet always faces its star
and basks in perpetual daylight, while the other is in perpetual
The most suitable place for life or future human colonists would be
in the 'grey' zone - the band between darkness and light that
circles the planet.
'Any emerging life forms would have
a wide range of stable climates to choose from and to evolve
around, depending on their longitude,' said Dr Vogt who reports
the find in the Astrophysical Journal.
If Gliese 581-g has a rocky composition
similar to the Earth's, its diameter would be about 1.2 to 1.4 times
that of the Earth.
It's gravity is likely to be similar - allowing a
human astronaut to walk on the surface upright without difficulty.
'This planet doesn't have days and
nights. Wherever you are on this planet, the sun is in the same
position all the time. You have very stable zones where the
ecosystem stays the same temperature... basically forever,' Vogt
Gliese 581, the
brightest object in this Nasa image from 2007,
is only 20 light
years from Earth and is one of our nearest neighbors
'If life can evolve, it's going to
have billions and billions of years to adapt to the surface.
Given the ubiquity of water, it seems probable that this thing
actually has liquid water. On the surface of the Earth,
everywhere you have liquid water you have life,' Vogt added.
Astronomers have now found six planets
in orbit around Gliese 581 - the most discovered in a planetary
system other than our own solar system.
Like the solar system, the planets orbiting Gliese 581 have mostly
Two of its detected planets have previously been proposed as
habitable planets. However they lie at the extremes of the
Goldilocks Zone - one on the hot side, the other on the cold side.
Gliese 581g, in contrast, lies right in the middle.
The star has not been given a proper name. It appears in a catalogue
of stars compiled by the German astronomer William Gliese where it
has been given the reference number 581.
Astronomers name planets found orbiting stars with a letter. The
previous five planets found around Gliese 581 were named b to f,
making the latest discovery Gliese 581-g.
Its star is a red giant - a massive star near the end of its life.
It is too dim to see in the night sky from Earth without a
Astronomers have found nearly 500 exoplanets - or planets outside
our own solar system. However, almost all are too big, made of gas
instead of rock, too hot or too cold for life as we know it.
The orbits of planets in the Gliese 581 system are compared to those
of our own solar system
The orbits of planets
in the Gliese 581 system
are compared to those
of our own solar system.
The Gliese 581 star
has about 30% the mass of our sun,
and the outermost
planet is closer to its star than we are to the sun.
The 4th planet, G, is
a planet that could sustain life.
More Evidence That Gliese 581...
Has Planets in The Habitable Zone
by Fraser Cain
December 14, 2007
The discovery of Gliese 581 was one of
the most exciting moments in extrasolar planetary researcher.
Astronomers found an Earth-massed planet
orbiting within the habitable zone of a distant star. This would
mean that liquid water could be on its surface - and maybe life.
there’s even more evidence that
is living up to the speculation. Astronomers have published
two independent studies this week, claiming that there are least 2
Earthlike planets orbiting the star within the habitability zone.
The first team, led by Franck Selsis, computed the properties
of planetary atmospheres at various distances from the star.
As we’ve seen with Venus, Earth and Mars
in our own Solar System, your distance from the star matters a great
deal. Get too close, and the water is vaporized and blown out into
space. Get too far away and your carbon dioxide can’t trap in enough
heat to keep the planet warm. You want to be just right.
Selsis and his team calculated that the inner boundary of this
habitable zone (below image) around Gliese 581 should be
somewhere between 0.7 and 0.9 astronomical units (an AU is the
distance from the Earth to the Sun ≈ 149,597,870.7 kilometers).
And the outer zone should be between 1.7
and 2.4 AU. At least one planet orbiting Gliese 581 falls within
The second team used a different technique to calculate
They studied a narrower region where
Earth-like photosynthesis is possible. For the super-Earths thought
to be orbiting Gliese 581, they calculated the sources of
atmospheric CO2 (volcanoes and ridges) and then the
potential sinks through weathering.
If a planet’s too old, if might not be
active any more, and wouldn’t release enough CO2 to keep
the planet warm.
Once again, the age of the planets, and
therefore the amount of carbon dioxide, is within this region of
Thanks to this new research, the planets orbiting Gliese 581 are
primary targets for future planet hunting observatories, such as
ESA’s Darwin and
NASA’s Terrestrial Planet Finder.
These observatories should be able to directly measure the
atmospheres of these planets, and determine if they harbor life.
A third paper on the topic has recently been accepted for
publication in the journal Astronomy and Astrophysics. In
this, another team of researchers have studied the long term orbits
of planets going around Gliese 581.
Here you want stability, without highly
eccentric orbits that might cause extreme warm and glacial eras.
Once again, the planets around Gliese 581 are surprisingly stable.
Things are looking really hopeful. Now we just need someone to
uncancel the Terrestrial Planet Finder.