""The search for exoplanets, or worlds orbiting other stars, is evolving so fast that discoveries that seemed exotic just a few months ago have become commonplace. Multiple-planet solar systems? Astronomers expected to find just a handful; now we know of more than 200. Planets orbiting double or even triple stars? It was big news when just one was announced back in September; we've already got several more examples in hand. In short, the unexpected is something planet hunters have learned to expect — and in most cases, these surprises have tended to expand the possibilities for finding worlds where life might thrive.
It's just happened again: astronomers from the Carnegie Institution of Washington and the University of California, Santa Cruz, writing in the Astrophysical Journal Letters, have announced the discovery of yet another new world that defies everyone's expectations. Not only does the new planet orbit one of the suns in a triple-star system — rare enough in itself — but the stars in this system have surprisingly low levels of the heavy elements planets are made from. Theory suggests that such stars shouldn't form planets in the first place, so if this isn't a fluke, there may be many more planets in the Milky Way than anyone thought. (See the best photos from space in 2011.)""
""That's not all: the new planet, called GJ667Cc, is just 4.5 times Earth's mass. That's big enough to qualify it for the astronomical label "super-Earth" but still quite small by exoplanet standards. Indeed, it's so small that GJ667Cc is thought to be made of earthlike rock rather than gas — even if those rocks had to coalesce from a smaller supply of raw material circling the parent sun. Beyond that, it orbits in its star's habitable zone: if there's water there, that water could be in life-friendly liquid form. GJ667Cc whips around its star once every 28 days or so; in our solar system, that would put it so scorchingly close to the sun that water would boil off. But the star in this case is an M-dwarf, much dimmer and redder than our own. Given its mass and its temperature, says co-discoverer Steve Vogt, of UC Santa Cruz, "I think it's going to be pretty historic. We've been gnawing at the bone of an earthlike planet in the habitable zone for years now, and I think we're just about there."""
""A new planet—probably a rocky super-Earth—has been found squarely within its star's habitable zone, making it one of the best candidates yet to support life, its discoverers say.
The planet, dubbed GJ 667Cc, orbits a red dwarf star 22 light-years from Earth, in the constellation Scorpio. A binary pair of orange dwarf stars are part of the same system.
(Related: "'Tatooine' Planet With Two Suns Could Host Habitable Moon?")
The new planet has a mass 4.5 times that of Earth and orbits its host star every 28 days.
The red dwarf is relatively dim, so the planet receives slightly less light from its star than Earth does from the sun. But most of the star's light is infrared, so the planet should absorb more of its incoming energy than Earth does from sunlight.
That means if the planet has a rocky surface—which is predicted for planets less than ten times Earth's mass—and an atmosphere, it could support liquid water and maybe life, said co-discoverer Guillem Anglada-Escudé, who conducted the work while at the Carnegie Institution for Science in Washington, D.C.
"If it has an atmosphere, it's probably reddish all the time, because the star is really red," Anglada-Escudé said. "It would be like being evening all the time."
For any hypothetical observers on the surface, the binary stars in the distance would be "very prominent in the sky, and it would be an exotic thing."""
""(Relaed: "New Planet May Be Among Most Earthlike—Weather Permitting.")
Rocky Planet Around Unexpected Star
Anglada-Escudé and colleagues found the new planet using public data from the European Southern Observatory, which hosts telescopes that can measure wobbles in a star's orbit caused by a planet's gravitational tug.
The new super-Earth was somewhat unexpected, because some planetary-formation models say that metal-poor stars such as GJ 667C shouldn't have terrestrial planets around them.""
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