Kepler spots two super Earths, one squarely in the habitable zone

Ars Technica » Scientific Method 2013-04-22

Liquid water is one of the essential ingredients of life on Earth and it has properties conducive to life in general, so researchers have defined the concept of a habitable zone with water as its focus. For astronomers, the habitable zone is the area far enough from a host star that a planet would be cool enough to support liquid water, but not so far that the water would be frozen. Although there are many caveats to this definition—everything from the presence of greenhouse gasses to clouds will shift a planet's average surface temperature—the concept helps drive the search for a planet capable of supporting life.

The caveats, however, have led to a number of arguments over whether a given exoplanet is likely able to host liquid water, with some candidates shifting in and out of the habitable zone more than once. Still, it's pretty clear that given the large number of reported candidate exoplanets, the odds suggest we've already spotted one. Today, scientists are announcing an exosolar system that has two planets that are both likely to be within the habitable zone, along with three others that are closer to the host star.

The findings come from the Kepler mission, which is dealing with a backlog of roughly 2,000 planet candidates to sort through and confirm. Normally, confirmation requires observing changes in the light emitted by the host star, which gets dragged closer to and further from the Earth as the planets circle it. However, this method requires that the planets either be large or orbiting close to the star so that their gravitational influence is big enough to shift it.

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