May 18, 2011

Free Floating Jupiter-Sized Planets Roam The Galaxy

NASA said on Wednesday that astronomers have discovered a new class of Jupiter-sized planets floating alone in space.

The astronomers believe these worlds were probably ejected from developing planetary systems.

A Japan-New Zealand joint survey scanned the center of the Milky Way galaxy during 2006 and 2007, revealing evidence for up to 10 free-floating planets about the size of Jupiter. 

"Although free-floating planets have been predicted, they finally have been detected, holding major implications for planetary formation and evolution models," Mario Perez, exoplanet program scientist at NASA Headquarters in Washington, said in a statement.

NASA said the scientists believe that there are hundreds of billions of lone planets in our Milky Way galaxy alone.

"Our survey is like a population census," David Bennett, a NASA and National Science Foundation-funded co-author of the study from the University of Notre Dame in South Bend, Ind, said in a statement. "We sampled a portion of the galaxy, and based on these data, can estimate overall numbers in the galaxy."

The astronomers say that theories suggest lower-mass planets like Earth should be ejected from their stars more often.

Previous studies found a handful of free-floating, planet-like objects within star-forming clusters.  However, scientists believe the gaseous bodies form more like stars than planets. 

NASA said some planets are ejected from their early solar systems due to close gravitational encounters with other planets or stars.  These planets move through the galaxy in stable orbits around the galaxy's center.

The discovery of 10 free-floating Jupiters supports the ejection scenario, though it is possible both mechanisms are at play.

"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 in a statement. "Our results suggest that planetary systems often become unstable, with planets being kicked out from their places of birth."

The space agency said that the observations cannot rule out the possibility that some of these planets may have a very distant orbit around stars. 

A 5.9-foot telescope at Mount John University Observatory in New Zealand is used to regularly scan the stars at the center of the Milky Way galaxy for gravitational microlensing events.

The Optical Gravitational Lensing Experiment (OGLE) also contributed to this discovery using a 4.2-foot telescope in Chile.

The study will be published on May 19 in the journal Nature.


Image Caption: This artist's conception illustrates a Jupiter-like planet alone in the dark of space, floating freely without a parent star. Image credit: NASA/JPL-Caltech


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