NASA planet hunters announce smallest exoplanet ever found, and close

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A tiny world of molten rock, orbiting scorchingly close to its host star, is the smallest planet ever discovered outside our solar system, NASA announced today. And it’s likely only the first in a parade of planet discoveries to be announced this spring by the Kepler Space Telescope team.

Kepler-10b, as the new world is called, is a rocky, dense and hellish planet just 1.4 times the size of Earth. It’s not in the Goldilocks zone, however — it’s much too close to its star for life to exist. It’s so hot (about 2,500 degrees F at the surface) that boiled iron and silicates are flowing into the stellar wind, much like a comet’s tail.

Kepler-10b is more than 20 times closer to its star than Mercury is to the sun, and it whips around the star once every 0.84 days. Its average density is comparable to that of an iron dumbbell, says NASA — about 8.8 grams per cubic centimeter, or 0.32 pounds per cubic inch.

Kepler’s super-precise camera was designed to spend three years staring at 150,000 Sun-like stars, searching for evidence of Earth-like planets. When a planet crosses the face of its star, called a transit, the star will get a tiny bit dimmer, and Kepler will notice the change.

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