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
Credit: Guillem Anglada-Escudé
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. "The star is quite red in colour. If the planet is rocky with an atmosphere the sky would look like a red sunset all the time."
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 might be.
"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."
