Two new free-floating planet candidates from microlensing
2018
Planetformation theories predict the existence of free-floating
planets, ejected from their parent systems. Although they emit little or no light, they can be detected during
gravitational microlensingevents. Microlensing events caused by
rogue planetsare characterized by very short timescales $t_{\rm E}$ (typically below two days) and small angular Einstein radii $\theta_{\rm E}$ (up to several uas). Here we present the discovery and characterization of two free-floating
planetcandidates identified in data from the Optical Gravitational Lensing Experiment (OGLE) survey. OGLE-2012-BLG-1323 is one of the shortest events discovered thus far ($t_{\rm E}$=0.155 +/- 0.005 d, $\theta_{\rm E}$=2.37 +/- 0.10 uas) and was caused by an
Earth-massobject in the Galactic disk or a
Neptune-mass
planetin the Galactic bulge. OGLE-2017-BLG-0560 ($t_{\rm E}$=0.905 +/- 0.005 d, $\theta_{\rm E}$=38.7 +/- 1.6 uas) was caused by a
Jupiter-mass
planetin the Galactic disk or a
brown dwarfin the bulge. We rule out stellar companions up to the distance of 6.0 and 3.9 au, respectively. We suggest that the lensing objects, whether located on very wide orbits or free-floating, may originate from the same physical mechanism. Although the sample of ultrashort microlensing events is small, these detections are consistent with low-mass wide-orbit or unbound
planetsbeing more common than stars in the Milky Way.
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