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New Super-Earth is Smallest Yet

Astronomershave discovered possibly the smallest extrasolar planet yet, a rocky worldthat?s orbiting a star in the constellation Leo.

?Afterfinal confirmation, the new exoplanet will be the smallest found to date,"said lead researcher Ignasi Ribas of the Spanish Research Council (CSIC)."The study opens a new path that should lead to the discovery of evensmaller planets in the near future, with the goal of eventually finding worldsmore and more similar to the Earth.?

The newlydiscovered planet weighs about five Earth masses and is located 30 light-yearsfrom Earth. A planet of this mass is expected to be rockyrather than gaseous, but there are no actual pictures of it. (A light-yearis the distance light travels in one year, or about 5.88 trillion miles ? 9.46trillion kilometers.)

That massmeans the planet is a "super-Earth," a category that includes planetswith masses of between one and 10 times the Earth. Astronomers estimate itsradius to be about 50 percent greater than that of Earth's radius of 4,000miles (6,400 kilometers).

Dubbed GJ436c, the planet orbits its host star (GJ 436) in just 5.2 Earth days, and isthought to complete a revolution about its axis in 4.2 Earth days. A completerevolution of Earth takes 24 hours and a full orbit around the sun takes 365days. ?

Theastronomers predicted the existence of the small exoplanet due to itsgravitational effects on the orbit of an inner planet ? a "hot iceplanet" discovered in 2004. In the new study, detailed this week in AstrophysicalJournal, the researchers found that for every two orbits of the hot ice planet, the newplanet completes one.

Most of the280 or so planets discovered to date outside of our solar system are muchlarger gas giants called "hot-Jupiters."

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