Unbound or distant planetary mass population detected by gravitational microlensing

• Published in: Nature (London) Vol. 473; no. 7347; pp. 349 - 352
• Main Authors: Sumi, T, Kamiya, K, Bennett, D P, Bond, IA, Abe, F, Botzler, C S, Fukui, A, Furusawa, K, Hearnshaw, J B, Itow, Y, Kilmartin, P M, Korpela, A, Lin, W, Ling, CH, Masuda, K, Matsubara, Y, Miyake, N, Motomura, M, Muraki, Y, Nagaya, M, Nakamura, S, Ohnishi, K, Okumura, T, Perrott, Y C, Rattenbury, N, Saito, To, Sako, T, Sullivan, D J, Sweatman, W L, Tristram, P J, Yock, PCM, Udalski, A, Szymaski, M K, Kubiak, M, Pietrzyski, G, Poleski, R, Soszyski, I, Wyrzykowski, Ulaczyk, K
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 19.05.2011; Nature Publishing Group
• Subjects: 639/766/33/445; Astronomical instruments; Astronomy; Astrophysics; Cosmic rays; Disks; Earth, ocean, space; Estimates; Exact sciences and technology; Extrasolar planetary systems; Extrasolar planets; Galactic bulge; Humanities and Social Sciences; Jupiter; letter; Light; multidisciplinary; Orbits; Photometric and spectroscopic detection ; coronographic detection ; interferometric detection; Science; Stars; Stars & galaxies; Uncertainty; Extrasolar planets; Abundance; Main sequence stars; Orbits; Milky Way; Proto planetary nebula; Young stars; Mass function; Sudden variation; Brown dwarf stars; Galactic bulge; Microlenses
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature10092

Lonely planets guide Gravitational microlensing observations in the direction of the Galactic Bulge have come up with a surprising result: the discovery of ten previously unknown extrasolar planets that are not bound to host stars. These seemingly free-ranging Jupiter-mass objects could be in very distant orbits around host stars, but no hosts could be detected within a distance of 10 astronomical units from the free-floating planets. It seems possible, therefore, that planet scattering is a routine part of the planet formation process. Since 1995, more than 500 exoplanets have been detected using different techniques 1 , 2 , of which 12 were detected with gravitational microlensing 3 , 4 . Most of these are gravitationally bound to their host stars. There is some evidence of free-floating planetary-mass objects in young star-forming regions 5 , 6 , 7 , 8 , but these objects are limited to massive objects of 3 to 15 Jupiter masses with large uncertainties in photometric mass estimates and their abundance. Here, we report the discovery of a population of unbound or distant Jupiter-mass objects, which are almost twice ( ) as common as main-sequence stars, based on two years of gravitational microlensing survey observations towards the Galactic Bulge. These planetary-mass objects have no host stars that can be detected within about ten astronomical units by gravitational microlensing. However, a comparison with constraints from direct imaging 9 suggests that most of these planetary-mass objects are not bound to any host star. An abrupt change in the mass function at about one Jupiter mass favours the idea that their formation process is different from that of stars and brown dwarfs. They may have formed in proto-planetary disks and subsequently scattered into unbound or very distant orbits.