Speaker
Description
We review the detection and mass-function measurements of free-floating planets (FFPs) or very wide-orbit planets using the microlensing technique. The microlensing surveys have identified several events with extremely short Einstein radius crossing times, t_E<0.5 days, and very small angular Einstein radii of theta_E <10μas. Such events are likely produced by low-mass lenses, potentially down to planetary masses.
MOA collaboration measure the mass function of FFP or very wide orbit planets down to an Earth mass, from the MOA-II microlensing survey in 2006-2014. Six events are likely to be due to planets with Einstein radius crossing times, t_E<0.5days, and the shortest has t_E = 0.057days and an angular Einstein radius of theta_E= 0.90 uas. For the first time, we evaluated the detection efficiency as a function of both t_E and theta_E with image level simulations. These short events are well modeled by a power-law mass function with a power-law index of 0.96^{+0.47}_{-0.27} for M/M_sun < 0.02. This result suggests that the FFPs were likely ejected from bound planetary systems whose initial mass function may have followed a similar power-law index of approximately 0.9. This model predicts that the Roman Space Telescope will detect about 1000 FFPs, with masses extending down to that of Mars. The PRIME telescope has begun a near-infrared microlensing survey toward the Galactic center to measure the masses of FFPs via space-based microlensing parallax in collaboration with Roman.
