2020/09/30 by P. Mroz, R. Poleski, A. Gould +27 · 1 citation
Physics and Astronomy · #astro-ph.EP #astro-ph.GA #astro-ph.IM
paper · pdf · doi:10.3847/2041-8213/abbfad
accepted for publication in ApJ Letters, minor changes
arxiv created 2020/10/20 · arxiv updated 2020/11/11
Some low-mass planets are expected to be ejected from their parent planetary systems during early stages of planetary system formation. According to planet-formation theories, such as the core accretion theory, typical masses of ejected planets should be between 0.3 and 1.0 M⊕. 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 uas) and extremely short timescales (< 0.1 day). Here, we present the discovery of the shortest-timescale microlensing event, OGLE-2016-BLG-1928, identified to date (t\rm E ≈ 0.0288 day = 41.5 min). 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 θ\rm E = 0.842 ± 0.064 uas, making the event the most extreme short-timescale microlens discovered to date. Depending on its unknown distance, the lens may be a Mars- to Earth-mass object, with the former possibility favored by the Gaia proper motion measurement of the source. The planet may be orbiting a star but we rule out the presence of stellar companions up to the projected distance of 8.0 au from the planet. Our discovery demonstrates that terrestrial-mass free-floating planets can be detected and characterized using microlensing.