Free-Floating Planets May Be More Common Than Stars May 18, 2011: Astronomers   
   have discovered a new class of Jupiter-sized planets floating alone in the   
   dark of space, away from the light of a star. The team believes these lone   
   worlds are probably outcasts from developing planetary systems and, moreover,   
   they could be twice as numerous as the stars themselves.   
       
   "Although free-floating planets have been predicted, they finally have been   
   detected," said Mario Perez, exoplanet program scientist at NASA Headquarters   
   in Washington. "[This has] major implications for models of planetary   
   formation and evolution."   
       
   The discovery is based on a joint Japan-New Zealand survey that scanned the   
   center of the Milky Way galaxy during 2006 and 2007, revealing evidence for up   
   to 10 free-floating planets roughly the mass of Jupiter. The isolated orbs,   
   also known as orphan planets, are difficult to spot, and had gone undetected   
   until now. The planets are located at an average approximate distance of   
   10,000 to 20,000 light years from Earth.   
   [...]   
   This artist's concept illustrates a Jupiter-like planet alone in the dark of   
   space, floating freely without a parent star. [larger image] [video]   
   This could be just the tip of the iceberg.  The team estimates there are about   
   twice as many free-floating Jupiter-mass planets as stars. In addition, these   
   worlds are thought to be at least as common as planets that orbit stars. This   
   adds up to hundreds of billions of lone planets in our Milky Way galaxy alone.   
       
   "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. "We sampled a portion of the galaxy, and   
   based on these data, can estimate overall numbers in the galaxy."   
       
   The study, led by Takahiro Sumi from Osaka University in Japan, appears in the   
   May 19 issue of the journal Nature. 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. As a result, they are   
   thought to be more common than free-floating Jupiters.   
       
   Previous observations spotted a handful of free-floating planet-like objects   
   within star-forming clusters, with masses three times that of Jupiter. But   
   scientists suspect the gaseous bodies form more like stars than 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.   
   It is thought the smallest brown dwarfs are approximately the size of large   
   planets.   
   [...]   
   A video from JPL describes the microlensing technique astronomers used to   
   detect the orphan planets. 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. Without a star to   
   circle, these planets would move through the galaxy as our sun and others   
   stars do, in stable orbits around the galaxy's center. The discovery of 10   
   free-floating Jupiters supports the ejection scenario, though it's 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. "Our   
   results suggest that planetary systems often become unstable, with planets   
   being kicked out from their places of birth."   
       
   The observations cannot rule out the possibility that some of these planets   
   may be in orbit around distant stars, but other research indicates   
   Jupiter-mass planets in such distant orbits are rare.   
       
   The survey, the Microlensing Observations in Astrophysics (MOA), is named in   
   part after a giant wingless, extinct bird family from New Zealand called the   
   moa. A 5.9-foot (1.8-meter) telescope at Mount John University Observatory in   
   New Zealand is used to regularly scan the copious stars at the center of our   
   galaxy for gravitational microlensing events. These occur when something, such   
   as a star or planet, passes in front of another more distant star. The passing   
   body's gravity warps the light of the background star, causing it to magnify   
   and brighten. Heftier passing bodies, like massive stars, will warp the light   
   of the background star to a greater extent,resulting in brightening events   
   that can last weeks. Small planet-size bodies will cause less of a distortion,   
   and brighten a star for only a few days or less.   
       
   A second microlensing survey group, the Optical Gravitational Lensing   
   Experiment (OGLE), contributed to this discovery using a 4.2-foot (1.3 meter)   
   telescope in Chile. The OGLE group also observed many of the same events, and   
   their observations independently confirmed the  analysis of the MOA group.   
       
   For more information about exoplanet research, visit http://plan   
   tquest.jpl.nasa.gov/  .   
       
       
   Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
       
   Lone Planet under a Cosmic Magnifying Glass -- JPL video   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.61   
    * Origin: NCS BBS (1:3828/7)