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Gaudi_2009_microlensing - The Demographics of Extrasolar...

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arXiv:0903.0880v1 [astro-ph.EP] 4 Mar 2009 The Demographics of Extrasolar Planets Beyond the Snow Line with Ground-based Microlensing Surveys White Paper for the Astro2010 PSF Science Frontier Panel B. Scott Gaudi The Ohio State University [email protected] 614-292-1914 J.P. Beaulieu 1 , David P. Bennett 2 , Ian A. Bond 3 , Subo Dong 4 , Andrew Gould 4 , Cheongho Han 5 , Byeong-Gon Park 6 , Takahiro Sumi 8 1 Institute d’Astrophysique de Paris 2 University of Notre Dame 3 Massey University 4 The Ohio State University 5 Chungbuk National University 6 Korea Astronomy and Space Science Institute 7 Nagoya University
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1. Overview In the currently-favored paradigm of planet formation, the location of the snow line in the protoplanetary disk plays a crucial role (e.g. Ida & Lin 2004). Determining the demographics of planets with masses of the Earth or larger beyond the snow line of stars of various masses is thus essential for testing this model. In the inner parts of this region, RV probes the gas giants but not the ice giants nor, of course, terrestrial planets. RV cannot make reliable measurements in the outer part of this region at all because the periods are too long. Future astrometry missions (such as SIM Lite ) could probe the inner regions down to terrestrial masses, but are also limited by their finite lifetime in the outer regions. Microlensing is sensitive to planets that are generally inaccessible to these other methods, and in particular is most sensitive to cool planets at or beyond the snow line, including very low-mass (i.e. terrestrial) planets. Hence, microlensing is uniquely suited and so essential for a comprehen- sive study of this region. Microlensing is also sensitive to planets orbiting low-mass stars, free-floating planets, planets in the Galactic bulge and disk, and even planets in external galaxies. These planets can also provide critical constraints on models of planet formation. In its final report, the ExoPlanet Task Force (Lunine et al. 2008) recognized the major role microlensing has to play in determining the demographics of planets throughout the Galaxy, writing that “[t]he statistics of planetary masses and separations available from a microlens- ing survey are vital for constraining the theory of planet formation.” They recommended that both ground and space-based microlensing be supported in the next 5-10 years. Here we focus on ground-based microlensing, and leave the discussion of space-based surveys for a separate paper (Bennett et al. 2009b). We briefly review the properties of and current results from the microlensing method (see Bennett 2009a for a more thorough discussion), and then outline the potential of, and progress toward, next generation ground-based microlensing surveys. Detailed models of such surveys have already been carried out, and the required network of 1-2m class tele- scopes with wide FOV instruments is beginning to be constructed by several countries, including Japan, New Zealand, Poland, and South Korea. The US still has a substantial role
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