It's not a planet in the conventional sense, because it doesn't orbit a star. Yet it's between four and seven times the mass of Jupiter, well within planetary size range. The object appears to be a young, cold planet in a cluster of about 30 stars moving together called AB Doradus, astronomers report in the December Astronomy & Astrophysics. The free-floating planet is the closest to Earth yet discovered, scientists say.
“It's quite a nice discovery probably the clearest example of a planetary mass object that's very young like this,” says astrophysicist Philip Lucas of the University of Hertfordshire in England, who was not involved with the study.
Other potential free-floating planets have been detected before, but their ages weren't as well known. Astronomers couldn't be sure the objects were planets and not brown dwarfs, failed stars too small to sustain fusion reactions in their cores.
The newfound object, dubbed CFBDSIR2149, lies in the southern constellation Dorado. Scientists estimate the planet is between 20 million and 200 million years old, based on the assumption that it was formed around the same time as the stars that it accompanies.
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