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Planet found at perfect spot for life - in solar system with three suns

Scientists have found a planet about 4.5 times the mass of Earth that orbits in the heart of its star's habitable zone, with two other suns orbiting much farther away. Is there water or the potential for life? Perhaps. But the planet could also be a two-faced world of scorching sun and perpetual ice.   

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Achieving synchronous rotation likely would happen within a billion years or so for an Earth-size planet, Dr. Comins says, especially if it has a moon, which also acts to slow the planet's rotation.

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For a super Earth, however, there might be hope. If the planet has no moon and is dense enough, the spin-down could take longer, allowing warmth to circulate and water to accumulate for a while longer before the big freeze and fry.

If a planet is in a elliptical orbit, which often is the case, the prospects are somewhat brighter, Comins suggests. The elliptical orbit would allow the planet to rotate and expose more of itself to light from its sun. Potentially habitable areas would fall in the twilight zone between hemispheres.

Some research suggests that the presence of the right kind of atmosphere could redistribute heat more readily than previously thought, “so it doesn't look that bad,” says Guillem Anglada-Escudé, a researcher at the University of Gottingen in Germany who led the international team.

Yet all of this remains speculation, he adds, until more is known about the planet.

How they found it

The discovery of GJ 667Cc emerged from a test Dr. Anglada-Escudé was making of new software, which was designed to analyze archived data to hunt for extrasolar planets. The team's planet-hunting approach measures the wobble that gravity from an orbiting planet imparts on its star.

The wobble shows up as back-and-forth shifts in the star's spectrum – a kind of bar code bearing information on the chemical elements present in the star's atmosphere. As the planet slips behind the star, the entire spectrum shifts toward red. When the planet tugs the star toward the observer, the star's spectrum shifts toward blue.

In 2009, researchers announced the discovery of a planet orbiting GJ 667C, with an orbital period of about 7 days. Last year, another team suggested a planet was orbiting with a 28-day period. But neither group provided any data or detailed analysis to back the claims. So Anglada-Escudé's team picked the system as the test dummy for its new detection software.

Not only did his team provide the first solid evidence of GJ 677Cb, a planet with 5.2 times Earth's mass orbiting the star every 7.2 days. It also found the super Earth in the habitable zone, as well as evidence for perhaps as many as two additional, more-distant planets.

The technique the team used, formally known as radial-velocity measurements, can provide only part of the picture, however. The team notes that there is a small chance that the orientation of the GJ 677C system could be just right, allowing scientists to watch the planets pass in front of their host star, an event called a transit. 

The star is bright enough and close enough that even amateur-class telescopes could detect any transits, Anglada-Escudé says. Such measurements would allow astronomers to determine more precisely the shape of the planets' orbits, and importantly, the planet's densities. The density estimates would allow a first cut at estimating what the planets are made of and what is in their atmospheres, if they have any.

Within two or three years, he adds, “we may have the capability of looking at the spectral features of the atmospheres of these planets, if they really transit.”

Accomplishing that “would be a real breakthrough,” he says.

The results of the team's research have been accepted for publication in Astrophysical Journal Letters.

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