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Potentially Habitable Planet Found Orbiting Nearby Star

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.

IfA astronomer Nader Haghighipour is a member of an international team of scientists that has discovered a potentially habitable orbiting a nearby star. The planet is categorized as a super-Earth planet, which means it is two to ten times more massive than Earth. This discovery demonstrates that habitable planets could form in a greater variety of environments than previously believed.

The 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.

"This planet is the new best candidate to support liquid water and, perhaps, life as we know it,” team leader Guillem Anglada-Escudé said. “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 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 Hawai‘i and the new Carnegie Planet Finder Spectrograph at the Magellan II Telescope in Chile. They used the planet-finding technique that involves measuring the small wobbles in a star’s orbit in response to a planet’s gravity.

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.

Haghighipour recently received a Humboldt Research Fellowship for Experienced Researchers  to work on planets in binary star systems. As part of that award, he will spend 2013 in Germany at the Max Planck Institute for Astronomy in Heidelberg and the University of Tübingen. Haghighipour has edited a book entitled Planets in Binary Star Systems, and he is a member of the planet-binary working group of the Kepler Space Telescope, which is searching for habitable planets.