New planet may support liquid water
by Becky Crew
8 February 2012
Artist's impression of newly discovered
extrasolar planet GJ 667Cc (in red) with GJ 667Cb and GJ 667Ca
(in yellow), which orbit the star GJ 667C
SYDNEY: A new extrasolar planet has been
identified and researchers are calling it the most likely
candidate yet to be able to host liquid water.
Publishing in the current issue of The
Astrophysical Journal Letters, an international team of
researchers led by Guillem Anglada-Escudé from the Carnegie
Institution for Science in the U.S describes a planet called GJ
667Cc, which is located at the relatively close distance of 22
light-years from Earth.
The planet belongs to a three or four planet
system and absorbs a similar amount of light from its star as
the Earth does from the Sun. If the planet is Earth-like in its
atmospheric and terrestrial composition, it would have the right
temperature to sustain liquid water, the researchers suggest.
"It lies in the region that we call the
'habitable zone' - if it was a rocky planet that looks just like
the Earth, it would be just the right distance from its star to
have the right temperature to host liquid water. And liquid
water is seen as an essential pre-condition for the development
of life," said co-author Chris Tinney from the University of New
South Wales in Sydney.
Detecting a new planet
In September last year, the European Organisation
for Astronomical Research's HARPS instrument was responsible for
the discovery of 50 new extrasolar planets orbiting parent
stars, including 16 new 'super-Earths', which are planets with a
mass between one and 10 times that of the Earth.
Together with data from the Keck Observatory's
High Resolution Echelle Spectrograph in California and the new
Carnegie Planet Finder Spectrograph at the Magellan II Telescope
in Chile, Anglada-Escudé analysed four years worth of data
collected by HARPS as it observed a star called GJ 667C.
Setting out to determine the orbital parameters
of GJ 667Cb - a 'super-Earth' that orbits GJ 667C over 7.2 days
- Anglada-Escudé applied a new planet-finding analytical
technique called 'the Doppled Wobble' to the data. This involves
measuring the small wobbles in a star's orbit in response to its
orbiting planet's gravity. In the process, Anglada-Escudé
detected the presence of a new planet.
"[Anglada-Escudé] downloaded data taken on this
star [GJ 667C] by the Harps spectroscope and developed new
technique for analysing it, uncovering evidence for new planet,"
said Tinney. "The is also evidence of planet with a 70-day
orbit, and another much longer orbital period 10 years or more."
Looks like a sunset
The researchers estimate that GJ 667Cc has an
orbital period of roughly 28.2 days and has a mass of around 4.5
times that of the Earth. It receives from its star GJ 667C 90%
of the light that the Earth receives from the Sun, but most of
it is in the infrared, so much more would be absorbed by the
planet. "This means that overall the planet absorbs about the
same amount of energy from its star as the Earth absorbs from
the Sun: so that would give the planet the right temperature, if
it has a rocky surface and a wet atmosphere, to host liquid
water," said Tinney. "If it's rocky, it would look quite red,
probably look like a sunset."
Whether or not this extrasolar planet has the
right surface temperature to sustain liquid water is wholly
reliant on the composition of its surface and atmosphere, but at
this stage, the researchers are unable to figure out what these
"We can't work out atmosphere. It could be rocky,
and it would be somewhat larger than the Earth if it had the
same density, or it could be very small version of Neptune,"
said Tinney. When asked if there's a possibility that it could
sustain life, Tinney replied, "If it's a planet that looks like
the Earth, it could, if it looks like Neptune, then it could be
life as we don't know it."
"This is a very interesting result, [but] it does
come with some caveats that should be kept in mind," commented
Charley Lineweaver from the Australian National University and
Mt Stromlo Observatory in Canberra. "Firstly, they [the
researchers] had to dig more than usual into the noise to detect
the planet and also, as the authors point out, uncertainties
about the planet's atmosphere means that we cannot be sure that
liquid water could exist at the surface."
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