Homeless planets may be common in our galaxy

Science : A long-running debate on whether free-floating planets really exist and how common they are may now be resolved, writes Jon Cartwright for Science. A new study by Takahiro Sumi of Osaka University in Japan and colleagues lists 10 objects in our galaxy that are very likely “homeless” planets and posits that such planets are more common than main-sequence stars, outnumbering them by nearly two to one. The team used a technique called gravitational microlensing to measure changes in the brightness of distant stars, whose light is bent and magnified by the gravity of planets passing in front of them. Smaller planets create shorter magnification times. The team found 474 incidents of microlensing, just 10 of which were brief enough to be planets of around Jupiter’s size, while the other 464 microlensing events were due to bigger objects such as brown dwarfs. One question arising from the study is how the free-floaters formed. According to one explanation, they used gravity to draw in nearby material such as the asteroids and protoplanets in our solar system. Sumi and his colleagues think it’s more likely that they began their lives in planetary systems and were subsequently thrown out of orbit.