New Super-Earth is Smallest Yet

Astronomers have discovered possibly the smallest extrasolar planet yet, a rocky world that?s orbiting a star in the constellation Leo.

?After final 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 even smaller planets in the near future, with the goal of eventually finding worlds more and more similar to the Earth.?

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

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

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

The astronomers predicted the existence of the small exoplanet due to its gravitational effects on the orbit of an inner planet ? a "hot ice planet" discovered in 2004. In the new study, detailed this week in Astrophysical Journal, the researchers found that for every two orbits of the hot ice planet, the new planet completes one.

Most of the 280 or so planets discovered to date outside of our solar system are much larger gas giants called "hot-Jupiters."

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