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

Abstract

Various methods have been proposed to search for extrasolar planets. Compared to the other methods, microlensing has unique applicabilities to the detections of Earth-mass and free-floating planets. However, the microlensing method is seriously flawed by the fact that the masses of the detected planets cannot be uniquely determined. Recently, Gould, Gaudi, & Han introduced an observational setup that enables one to resolve the mass degeneracy of the Earth-mass planets. The setup requires a modest adjustment to the orbit of an already proposed microlensing planet-finder satellite combined with ground-based observations. In this paper, we show that a similar observational setup can also be used for the mass determinations of free-floating planets with masses ranging from several Earth masses to several Jupiter masses. If the proposed observational setup is realized, future lensing surveys will play important roles in the studies of Earth-mass and free-floating planets, which are the populations of planets that have not been previously probed.