Detecting Exomoons in Free-floating-planet Events from Space-based Microlensing Surveys 后印本

摘要: When a planet is ejected from its star-planet system due to dynamical interactions, its satellite may remain gravitationally bound to the planet. The Chinese Space Station Telescope (CSST) will be capable of detecting a large number of low-mass free-floating planet events (FFPs) from a bulge microlensing survey. We assess the feasibility of detecting satellites (a.k.a., exomoons) orbiting FFPs by simulating CSST light curves and calculating the detection efficiency as a function of satellite-to-planet mass ratios (q) and projected separations (s) in units of the Einstein radius. For a Neptune-class FFP in the Galactic disk with a Sun-like star as the microlensed source,CSST can detect Earth-mass satellites over a decade of separations (∼0.01–0.1 au) and has sensitivity down to Moon-mass satellites (q ∼ 10−3) at s ∼ 1. CSST also has some sensitivity to detect Moon-mass satellites at s ∼ 2 (∼0.02 au) orbiting an Earth-mass FFP in the disk. CSST has substantially reduced sensitivity for detecting satellites when the source star is an M dwarf,compared to a Sun-like source. We also calculate the satellite detection efficiency for the dedicated microlensing survey of the Roman Space Telescope (Roman),which demonstrates greater sensitivity than CSST,particularly for M-dwarf sources. Notably,some of the Neptune-Earth systems detectable by CSST and Roman may exhibit significant tidal heating.