Since 1995, more than 500 exoplanets have been detected using differenttechniques, of which 11 were detected with gravitational microlensing. Most ofthese are gravitationally bound to their host stars. There is some evidence offree-floating planetary mass objects in young star-forming regions, but theseobjects are limited to massive objects of 3 to 15 Jupiter masses with largeuncertainties in photometric mass estimates and their abundance. Here, wereport the discovery of a population of unbound or distant Jupiter-massobjects, which are almost twice (1.8_{-0.8}^{+1.7}) as common as main-sequencestars, based on two years of gravitational microlensing survey observationstoward the Galactic Bulge. These planetary-mass objects have no host stars thatcan be detected within about ten astronomical units by gravitationalmicrolensing. However a comparison with constraints from direct imagingsuggests that most of these planetary-mass objects are not bound to any hoststar. An abrupt change in the mass function at about a Jupiter mass favours theidea that their formation process is different from that of stars and browndwarfs. They may have formed in proto-planetary disks and subsequentlyscattered into unbound or very distant orbits.
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