Mysterious "Super Earth" Is Smallest Known Exoplanet?

April 11, 2008

The eccentric orbit of a Neptune-like planet could be evidence that the distant gas giant has a smaller, rocky neighbor, astronomers say.

If confirmed, the new terrestrial world will be one of the least massive exoplanets known to orbit a sunlike star and only the second known warm "super Earth."

Although they are five or more times as massive as our world, super-Earths are thought to be rocky rather than gaseous—which makes them strong candidates for harboring life.

Ignasi Ribas of the Spanish National Research Council in Bellaterra and colleagues describe the possible new world in the April 6 issue of The Astrophysical Journal.

Ribas and colleagues say the planet, dubbed GJ 436c, orbits a red dwarf star about 30 light-years away in the constellation Leo.

According to the study team, GJ 436c would also be the first exoplanet revealed by its affect on the orbit of a planetary neighbor.

"Because of this," Ribas said, "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."

Four-Year-Long Day

Ribas and colleagues predicted GJ 436c after noticing that GJ 436b, the known Neptune-like exoplanet, passed in front of its host star in 2007. Observations in 2004 had not revealed such a transit.

Computer models of the system therefore suggested that another world was affecting the gas giant's orbit.

The models predict that the new planet is a rocky type with a radius some 50 percent larger than Earth's.

Temperatures on the planet range between 260 and 800 degrees Fahrenheit (127 and 427 degrees Celsius), the team calculated.

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