Artist's conception of GJ 667C with planet GJ 667Cc on the right.
An international team of scientists that includes University of Hawaiʻi at Mānoa astronomer Nader Haghighipour has discovered a potentially habitable super-Earth planet orbiting a nearby star. This discovery demonstrates that habitable planets could form in a greater variety of environments than previously believed.
“This planet is the new best candidate to support liquid water and, perhaps, life as we know it,” said team leader Guillem Anglada-Escudé.
Super-Earth planets are two to ten times more massive than Earth.
The team used the planet-finding technique that involves measuring the small wobbles in a star’s orbit in response to a planet’s gravity. An M-class dwarf star called GJ 667C, which is 22 light-years away from Earth, had previously been observed to have a super-Earth (called GJ 667Cb) that orbited the star in only 7.2 days, making it too close to the star, and thus too hot, to support life.
The study started with the aim of learning more about the orbit of GJ 667Cb. However, the research team found a clear signal of a new planet (GJ 667Cc) with an orbital period of 28.15 days and a minimum mass of 4.5 times that of Earth.
The new planet receives 90 percent of the light that Earth receives. However, because most of its incoming light is heat (infrared light), a higher percentage of this incoming energy should be absorbed by the planet. When both these effects are taken into account, GJ 667Cc should absorb about the same amount of energy from its star that Earth absorbs from the sun. This would allow surface temperatures similar to Earth and perhaps liquid water, but this cannot be confirmed without further information on the planet’s atmosphere.
“The detection of this planet is strong evidence that our strategy in choosing M stars as potential hosts for habitable planet is correct and has been successful,” said Haghighipour, who works at UH Mānoa’s Institute for Astronomy and is a member of the UH NASA Astrobiology Institute. M stars are smaller than the sun.
The team used public data from the European Southern Observatory and analyzed it with a novel data analysis method. They also incorporated new measurements from the Keck Observatory’s High Resolution Echelle Spectrograph in Hawaiʻi and the new Carnegie Planet Finder Spectrograph at the Magellan II Telescope in Chile.
GJ 667C is a member of a triple-star system and has less metallic elements (those heavier than hydrogen and helium) than our sun. The other two stars in the triple system (GJ 667AB) also have a small concentration of heavy elements. Since such elements are the building blocks of terrestrial planets like Earth, the team thought it was unusual for a metal-depleted star system to have an abundance of low-mass planets.
The work on this project will be published in The Astrophysical Journal Letters
. The current version of the manuscript is posted at http://arxiv.org/abs/1202.0446
Anglada-Escudé was with Carnegie Institution for Science when he conducted the research, but has since moved on to the University of Gottingen. The co-authors in addition to Haghighipour are Carnegie’s Paul Butler, Jeffrey D. Crane, Stephen A. Shectman, and Ian B. Thompson; Pamela Arriagada and Dante Minniti of Pontificia Universidad Catolica de Chile; Steve Vogt and Eugenio J. Rivera of University of California’s Lick Observatory; Brad D. Carter of University of Southern Queensland; C. G. Tinney, Robert A. Wittenmyer, and Jeremy A. Bailey of the University of New South Wales; Simon J. O’Toole of the Australian Astronomical Observatory; Hugh R. A. Jones of the University of Hertfordshire; and James S. Jenkins of the Universidad de Chile, Camino El Observatorio.