OGLE and KMTNet light curve of OGLE-2016-BLG-1928

According to planet formation theories, such as the core accretion theory, typical masses of ejected planets should be between 0.3 and 1.0M{Earth}. Although in practice such objects do not emit any light, they may be detected using gravitational microlensing via their light-bending gravity.

Microlensing events due to terrestrial-mass rogue planets are expected to have extremely small angular Einstein radii (<~1{mu}as) and extremely short timescales (<~0.1day). Here, we present the discovery of the shortest-timescale microlensing event, OGLE-2016-BLG-1928, identified to date (t_E_~0.0288day=41.5min. Thanks to the detection of finite-source effects in the light curve of the event, we were able to measure the angular Einstein radius of the lens {theta}_E_=0.842{+/-}0.064{mu}as, making the event the most extreme short-timescale microlens discovered to date.