mountain profile Institute for Astronomy University of Hawaii

Potentially habitable planet found orbiting nearby star

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For immediate release
February 2, 2012


Dr .Nader Haghighipour

Ms. Louise Good
Media Contact



GJ667C planetary system
GJ 667C planetary system showing the orbits of the planets b, c (the potentially habitable one), and d (not yet confirmed). The habitable zone (HZ) in which liquid water could exist is shown in blue. The outer gray circle could be an extended HZ if a planet's atmosphere contains a large amount of warming carbon dioxide (CO2). An astronomical unit (AU) is the distance between Earth and the sun. Click on picture for larger view. Credit: G. Anglada-Escudé.

An international team of scientists that includes University of Hawaii at Manoa 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,” team leader Guillem Anglada-Escudé said.

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. But 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 Manoa’s Institute for Astronomy and is a member of the UH NASA Astrobiology Institute. M stars are smaller than our 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 Hawaii 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

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.

Other illustrations

Figure 1: Comparative liquid water habitable zones for our solar system and the GJ 667C planetary system. The gray areas indicate the theoretical inner edge for different fractional cloud coverage. The outer edge is marked with a dashed line. Credit: G. Anglada-Escudé et al.

Figure 2: Artist's conception of GJ 667C. The size of the star and the binary are shown at the right scale, color and brightness. Credit: G. Anglada-Escudé using the program Celestia.

Figure 3: Artist's conception of the two planets b and c. Planet c is the one that lies in the habitable zone of the star. Planet b is too hot to be habitable. Credit: G. Anglada-Escudé using the program Celestia.

Figure 4: Same as Figure 3 with labels.

Figure 5: Sky location of the GJ 667 system in the constellation Scorpius. The system is a bit faint to be visible with the naked eye (V = 5.8), but you may be able to see it under extremely good conditions. Credit: G. Anglada-Escudé using the program Celestia.

Figure 6: The GJ 667C triple system as seen from a telescope. Image generated with Aladdin using images from the Digitized Sky Survey. Credit: G. Anglada-Escudé.

Founded in 1967, the Institute for Astronomy at the University of Hawaii at Manoa conducts research into galaxies, cosmology, stars, planets, and the sun. Its faculty and staff are also involved in astronomy education, deep space missions, and in the development and management of the observatories on Haleakala and Mauna Kea.

Established in 1907 and fully accredited by the Western Association of Schools and Colleges, the University of Hawaii is the state's sole public system of higher education. The UH System provides an array of undergraduate, graduate, and professional degrees and community programs on 10 campuses and through educational, training, and research centers across the state. UH enrolls more than 50,000 students from Hawaii, the U.S. mainland, and around the world.