Simulation of a Space‐based Microlensing Survey for Terrestrial Extrasolar Planets

We show that a space-based gravitational microlensing survey for terrestrialextra-solar planets is feasible in the near future, and could provide a nearlycomplete picture of the properties of planetary systems in our Galaxy. Wepresent simulations of such a survey using a 1-2m aperture space telescope witha ~2 square degree field-of-view which is used to continuously monitor ~10^8Galactic bulge main sequence stars. The microlensing techniques allows thediscovery of low mass planets with high signal-to-noise, and the space missionthat we have studied are sensitive to planets with masses as low as that ofMars. By targeting main sequence source stars, which can only be resolved fromspace, the space-based microlensing survey is able to detect enough light fromthe lens stars to determine the spectral type of one third of the lens starswith detected planets, including virtually all of the F, G, and K stars whichcomprise one quarter of the event sample. This enables the determination of theplanetary masses and separations in physical units, as well as the abundance ofplanets as a function of stellar type and distance from the Galactic center. Weshow that a space-based microlensing planet search program has its highestsensitivity to planets at orbital separations of 0.7-10 AU, but it will alsohave significant sensitivity at larger separations and will be able to detectfree-floating planets in significant numbers. This complements the plannedterrestrial planet transit missions which are sensitive to terrestrial planetsat separations of =< 1 AU. Such a mission also detect ~50,000 giant planets viatransits, and it is, therefore, the only proposed planet detection method thatis sensitive to planets at all orbital radii.