An international team of scientists has discovered a massive new planet thanks to a phenomenon predicted by Einstein 70 years ago. Microlensing occurs when a star crosses in front of another star and bends the light from the more distant star, magnifying it like a lens. Astronomers recently took advantage of one such occlusion to get a better look at a red dwarf star roughly 9,000 light years from Earth, known as BLG-169. It appeared even brighter than expected. Only a star with a planet could have produced this effect, they say.

Based on the more than 1,000 images from the MDM Observatory in Arizona, team leader Andrew Gould of Ohio State University and his fellow astronomers calculate that this new planet has roughly 13 times the mass of Earth--making it about the size of Neptune--and orbits its star at about the distance of the asteroid belt in our own solar system. The researchers suspect that it is a cold, rocky world, with temperatures around -330 degrees Fahrenheit--perhaps a gas supergiant in the making that failed to attract or didn't have access to gaseous material.

Although it is only the fifth Neptune-size planet discovered (all in the last decade) this type of object may be fairly common in the Milky Way. Current theory predicts that smaller stars should encourage the formation of smaller planets and, because most stars in this galaxy are red dwarfs, such planets may be more common than the 170 or so Jupiter-size orbs discovered so far. "These icy super-Earths are pretty common--roughly 35 percent of all stars have them," Gould says. "The next step is to push the sensitivity of our detection methods down to reach Earth-mass planets, and microlensing is the best way to get there." A paper detailing the findings was published online earlier this week in Astrophysical Journal Letters.

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