Hot Earth orbits closest star system

by Ken Croswell
Tuesday, October 16, 2012

A hot Earth-sized planet circles Alpha Centauri, the sun's nearest stellar neighbor, a team of astronomers led by Xavier Dumusque of the University of Geneva reports this week in Nature. They detected the tiny gravitational tug this world exerts on its star.

Researchers had feared that Alpha Centauri might be planetless, because it consists of three separate suns. Thus, gravitational forces from one star might have thwarted the formation of planets around another. The two brightest stars, named Alpha Centauri A and B, lie just 4.37 light-years from Earth and emit roughly as much light as the sun: One is yellow, the other orange, and they orbit each other every 80 years. A dim red dwarf star orbits them; it's slightly closer to us, 4.24 light-years from Earth, so it's named Proxima Centauri.

The newfound planet circles Alpha Centauri B, the orange star, every 3 days, 5 hours, and 40 minutes. The planet is one-ninth as far from its sun as Mercury is from ours, so it must be torrid and lifeless. But the discovery, if confirmed, suggests Alpha Centauri could boast Earth-sized planets that sport mild climates, liquid water, and even some form of life.

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