The Milky Way galaxy may be filled with millions upon millions of Jupiter-sized planets that have escaped their solar systems and are wandering freely in space, researchers said Wednesday in a finding that seems certain to make astronomers rethink their ideas about planetary formation.
Scientists had previously thought that about 20% of stars had massive planets attached to them, but the new results reported in the journal Nature suggest that there are at least twice as many planets as stars, and perhaps several times as many.
The finding "is a revelation in the sense that it looks like a quintupling of the number of gas giants in the universe," said astronomer Alan Boss of the Carnegie Institution for Science, who was not involved in the research.
Scientists have long speculated that some planets may be vagabonds in interstellar space, but with these observations, "for the first time, we have fairly strong evidence that indeed this is happening," said Caltech astronomer David Stevenson, who also was not involved in the research.
The discoverers of the wandering planets speculate that the orphan bodies were ejected from formative solar systems soon after they condensed from the interstellar dust that also formed the stars.
"If they are ejected, it's a real puzzle as to how that happened because you have to be kicked out by something bigger than you," Boss said.
The finding will have "theorists scratching their heads and sharpening their pencils for some time to come," he added.
The orphan planets were discovered by an international team of astronomers headed by Takahiro Sumi of Osaka University in Japan. The team used the 5.9-foot telescope at Mount John University Observatory in New Zealand to regularly scan the innumerable stars at the center of the galaxy to search for so-called gravitational microlensing events.
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