A new planet that is the most likely candidate yet identified to be able to host liquid water has been found by an international team of astronomers.
The planet, GJ 667Cc, lies only 22 light-years from Earth. It circles a relatively cool star (GJ667C), has an orbital period of 28.15 days and a minimum mass of 4.5 times that of Earth, according to a report of the discovery to be published in The Astrophysical Journal Letters.
The new planet receives about 90% of the light that the Earth receives from the Sun. But most of this incoming light is in the infrared, and so more of it will be absorbed by the planet, says Professor Chris Tinney of the University of NSW, a member of the research team. Other UNSW team members include Dr Jeremy Bailey and Dr Rob Wittenmyer.
“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,” says Professor Tinney. “And liquid water is seen as an essential pre-condition for the development of life.”
The planet orbits a star called GJ 667C, which is a member of a triple-star system and orbits a distant pair of brighter, orange K-dwarfs (GJ 667A and B).
“This discovery shows that habitable planets could form in a greater variety of environments than we previously considered,” said Dr Simon O’Toole of the Australian Astronomical Observatory, another team member.
The planet was discovered using the “Doppler wobble” technique, which detects the slight movements of a star as its orbiting planets tug it to and fro in space.
Star GJ 667C had previously been observed to have a “super-Earth” (GJ 667Cb) with an orbital period of 7.2 days, although this finding was never published. But that orbit is too tight, and thus that planet is too hot, to support life.
GJ 667C might also host a distant gas-giant planet, and an additional super-Earth with an orbital period of 75 days, but more observations are needed to confirm this.
Data that led to the finding came from the European Southern Observatory’s 3.6m telescope; one of the two 6.5-m Magellan telescopes of the Carnegie Observatories; and one of the twin 10-m Keck telescopes operated by the University of California and the California Institute of Technology.
Dr Brad Carter of the University of Southern Queensland was one of several astronomers who made observations for the project—in his case, using Magellan in Chile.
This project was part of a larger program to find rocky planets and super-Earths.