An Earth-mass Planet in a 1-AU Orbit around an Ultracool Dwarf
Shvartzvald et al
We combine Spitzer and ground-based KMTNet microlensing observations to identify and precisely measure an Earth-mass (1.43+0.45−0.32M⊕) planet OGLE-2016-BLG-1195Lb at 1.16+0.16−0.13 AU orbiting a 0.078+0.016−0.012M⊙ ultracool dwarf. This is the lowest-mass microlensing planet to date. At 3.91+0.42−0.46 kpc, it is the third consecutive case among the Spitzer "Galactic distribution" planets toward the Galactic bulge that lies in the Galactic disk as opposed to the bulge itself, hinting at a skewed distribution of planets. Together with previous microlensing discoveries, the seven Earth-size planets orbiting the ultracool dwarf TRAPPIST-1, and the detection of disks around young brown dwarfs, OGLE-2016-BLG-1195Lb suggests that such planets might be common around ultracool dwarfs. It therefore sheds light on the formation of both ultracool dwarfs and planetary systems at the limit of low-mass protoplanetary disks.