![]() The observations cannot rule out the possibility that some of these planets may have very distant orbits around stars, but other research indicates Jupiter-mass planets in such distant orbits are rare. “Our results suggest that planetary systems often become unstable, with planets being kicked out from their places of birth.” “If free-floating planets formed like stars, then we would have expected to see only one or two of them in our survey instead of 10,” Bennett said. ![]() ![]() The discovery of 10 free-floating Jupiters supports the ejection scenario, though it’s possible both mechanisms are at play. Without a star to circle, these planets would move through the galaxy as our sun and other stars do, in stable orbits around the galaxy’s center. On the other hand, it is likely that some planets are ejected from their early, turbulent solar systems, due to close gravitational encounters with other planets or stars. It is thought the smallest brown dwarfs are approximately the size of large planets. These small, dim orbs, called brown dwarfs, grow from collapsing balls of gas and dust, but lack the mass to ignite their nuclear fuel and shine with starlight. But scientists suspect the gaseous bodies form more like stars than planets. Previous observations spotted a handful of free-floating, planet-like objects within star-forming clusters, with masses three times that of Jupiter. As a result, they are thought to be more common than free-floating Jupiters. The survey is not sensitive to planets smaller than Jupiter and Saturn, but theories suggest lower-mass planets like Earth should be ejected from their stars more often. The study, led by Takahiro Sumi from Osaka University in Japan, appears in the May 19 issue of the journal Nature. “We sampled a portion of the galaxy, and based on these data, can estimate overall numbers in the galaxy.” “Our survey is like a population census,” said David Bennett, a NASA and National Science Foundation-funded co-author of the study from the University of Notre Dame in South Bend, Ind. This would add up to hundreds of billions of lone planets in our Milky Way galaxy alone. In addition, these worlds are thought to be at least as common as planets that orbit stars. The team estimates there are about twice as many of them as stars. The discovery indicates there are many more free-floating Jupiter-mass planets that can’t be seen. “Although free-floating planets have been predicted, they finally have been detected, holding major implications for planetary formation and evolution models,” said Mario Perez, exoplanet program scientist at NASA Headquarters in Washington. The newfound planets are located at an average approximate distance of 10,000 to 20,000 light-years from Earth. The isolated orbs, also known as orphan planets, are difficult to spot, and had gone undetected until now. The discovery is based on a joint Japan-New Zealand survey that scanned the center of the Milky Way galaxy during 20, revealing evidence for up to 10 free-floating planets roughly the mass of Jupiter. The team believes these lone worlds were probably ejected from developing planetary systems. Astronomers, including a NASA-funded team member, have discovered a new class of Jupiter-sized planets floating alone in the dark of space, away from the light of a star.
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