Detecting Earth‐Mass Planets with Gravitational Microlensing

Abstract

We show that Earth mass planets orbiting stars in the Galactic disk and bulge\ncan be detected by monitoring microlensed stars in the Galactic bulge. The star\nand its planet act as a binary lens which generates a lightcurve which can\ndiffer substantially from the lightcurve due only to the star itself. We show\nthat the planetary signal remains detectable for planetary masses as small as\nan Earth mass when realistic source star sizes are included in the lightcurve\ncalculation. These planets are detectable if they reside in the ``lensing zone"\nwhich is centered between 1 and 4 AU from the lensing star and spans about a\nfactor of 2 in distance. If we require a minimum deviation of 4\\% from the\nstandard point-lens microlensing lightcurve, then we find that more than 2\\% of\nall $\\mearth$ planets and 10\\% of all $10\\mearth$ in the lensing zone can be\ndetected. If a third of all lenses have no planets, a third have $1\\mearth$\nplanets and the remaining third have $10\\mearth$ planets then we estimate that\nan aggressive ground based microlensing planet search program could find one\nearth mass planet and half a dozen $10\\mearth$ planets per year.\n