Gravitational Microlensing: A Tool for Detecting and Characterizing Free‐Floating Planets

Various methods have been proposed to search for extrasolar planets. Comparedto the other methods, microlensing has unique applicabilities to the detectionsof Earth-mass and free-floating planets. However, the microlensing method isseriously flawed by the fact that the masses of the detected planets cannot beuniquely determined. Recently, Gould, Gaudi, & Han introduced an observationalsetup that enables one to resolve the mass degeneracy of the Earth-massplanets. The setup requires a modest adjustment to the orbit of an alreadyproposed Microlensing planet-finder satellite combined with ground-basedobservations. In this paper, we show that a similar observational setup canalso be used for the mass determinations of free-floating planets with massesranging from ~0.1 M_J to several Jupiter masses. If the proposed observationalsetup is realized, the future lensing surveys will play important roles in thestudies of Earth-mass and free-floating planets, which are the populations ofplanets that have not been previously probed.Comment: total 8 pages, including 3 figures, ApJ, in press (Mar 1, 2004