A potentially habitable alien planet — one that scientists say is the best candidate yet to harbor water, and possibly even life, on its surface — has been found around a nearby star.
The planet is located in the habitable zone of its host star, which is a narrow circumstellar region where temperatures are neither too hot nor too cold for liquid water to exist on the planet's surface.
"It's the Holy Grail of exoplanet research to find a planet around a star orbiting at the right distance so it's not too close where it would lose all its water and boil away, and not too far where it would all freeze," Steven Vogt, an astronomer at the University of California, Santa Cruz, told SPACE.com. "It's right smack in the habitable zone — there's no question or discussion about it. It's not on the edge, it's right in there."
Vogt is one of the authors of the new study, which was led by Guillem Anglada-Escudé and Paul Butler of the Carnegie Institution for Science, a private, nonprofit research organization based in Washington, D.C.
"This planet is the new best candidate to support liquid water and, perhaps, life as we know it," Anglada-Escudé said in a statement.
An alien super-Earth
The researchers estimate that the planet, called GJ 667Cc, is at least 4.5 times as massive as Earth, which makes it a so-called super-Earth. It takes roughly 28 days to make one orbital lap around its parent star, which is located a mere 22 light-years away from Earth, in the constellation Scorpius (the Scorpion).
"This is basically our next-door neighbor," Vogt said. "It's very nearby. There are only about 100 stars closer to us than this one."
Interestingly enough, the host star, GJ 667C, is a member of a triple-star system. GJ 667C is an M-class dwarf star that is about a third of the mass of the sun, and while it is faint, it can be seen by ground-based telescopes, Vogt said. [Gallery: The Strangest Alien Planets]
"The planet is around one star in a triple-star system," Vogt explained. "The other stars are pretty far away, but they would look pretty nice in the sky."
The discovery of a planet around GJ 667C came as a surprise to the astronomers, because the entire star system has a different chemical makeup than our sun. The system has much lower abundances of heavy elements (elements heavier than hydrogen and helium), such as iron, carbon and silicon.
"It's pretty deficient in metals," Vogt said. "These are the materials out of which planets form — the grains of stuff that coalesce to eventually make up planets — so we shouldn't have really expected this star to be a likely case for harboring planets."
The fortuitous discovery could mean that potentially habitable alien worlds could exist in a greater variety of environments than was previously thought possible, the researchers said.
"Statistics tell us we shouldn't have found something this quickly this soon unless there's a lot of them out there," Vogt said. "This tells us there must be an awful lot of these planets out there. It was almost too easy to find, and it happened too quickly."
The detailed findings of the study will be published in the Astrophysical Journal Letters.