Rocky Planet Goes to Extremes

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NEW YORK — The first rocky planet confirmed to be orbiting another star is truly one strange world, with rock rains, potentially raging volcanoes and huge temperature differences between its night and day sides. This rock might be the remnant core of a former gas giant whose atmosphere long ago evaporated away.

CoRoT-7b, named after the French telescope that discovered it, is a so-called super-Earth orbiting a star about 480 light-years from Earth.

At five times the mass of Earth and not quite two times the Earth’s radius, this extrasolar planet was the first of the more than 400 that have been found to date that was confirmed to be a rocky world instead of a gas giant. But this exoplanet is anything but Earth-like.

CoRoT-7b orbits just 2.5 million kilometers out from its parent star, or 23 times closer than Mercury is to the sun in our solar system. This close proximity sends temperatures on the star-facing side of the planet up to 2,200 degrees Celsius.

The planet is tidally locked, meaning the same side is always facing its star — just as the Moon only presents one face to the Earth. The far side of the planet is therefore always in shadow, and temperatures there dip down as low as minus 210 degrees Celsius.

The possibility that CoRoT-7b’s current appearance may be the shriveled remains of a former gas giant also casts another oddity atop the pile. “CoRoT-7b may be the first in a new class of planet — evaporated remnant cores,” said Brian Jackson of NASA’s Goddard Space Flight Center in Greenbelt, Md.

The temperatures on the star-facing side of the planet are so hot they can vaporize rock. Scientists who modeled the atmosphere of CoRoT-7b determined that the planet likely has no volatile gases such as carbon dioxide, water vapor or nitrogen, and is instead likely made up of what could be called vaporized rock. The atmosphere could have weather systems that cause pebbles to condense out of the air and rain rocks onto the molten surface of the planet.

The planet also could be a hotbed of volcanic activity. New evidence presented recently at the annual meeting of the American Astronomical Society in Washington suggests that if CoRoT-7b’s orbit is not perfectly circular, gravitational tugs from one of its two sister planets could push and pull the surface, creating friction that heats the interior of the planet. This heating could cause extensive volcanism across the planet’s surface, with even more explosive activity than Jupiter’s moon Io, which has over 400 volcanoes.