by Mike Wall, Senior Writer
Date: 16 October 2012 Time: 05:58 PM ET

The star system closest to our own sun hosts a planet with roughly Earth’s mass and may harbor other alien worlds as well, a new study reports.

Astronomers detected the alien planet around the sunlike star Alpha Centauri B, which is part of a three-star system just 4.3 light-years away from us. The newfound world is about as massive as Earth, but it’s no Earth twin; its heat-blasted surface may be covered with molten rock, researchers said.

The mere existence of the planet, known as Alpha Centauri Bb, suggests that undiscovered worlds may lurk farther away from its star — perhaps in the habitable zone, that just-right range of distances where liquid water can exist.

“Most of the low-mass planets are in systems of two, three to six or seven planets, out to the habitable zone,” study co-author Stephane Udry, of the Geneva Observatory, told reporters today (Oct. 16).

So the discovery “opens really good prospects for detecting planets in the habitable zone in a system that is very close to us,” Udry added. “In that sense, this system is a landmark.”

Alpha Centauri Bb zips around its star every 3.2 days, orbiting at a distance of just 3.6 million miles (6 million kilometers). For comparison, Earth orbits about 93 million miles, or 150 million km, from the sun. [Gallery: Nearby Alien Planet Alpha Centauri Bb]

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