# An Earth-mass Planet in a 1-AU Orbit around an Ultracool Dwarf

## TL;DR

This paper reports the discovery of the lowest-mass microlensing planet to date, an Earth-mass planet orbiting an ultracool dwarf at 1 AU, providing insights into planet formation around very low-mass stars.

## Contribution

It presents the first precise measurement of an Earth-mass planet around an ultracool dwarf via microlensing, expanding knowledge of planetary systems in low-mass environments.

## Key findings

- The planet has a mass of approximately 1.43 Earth masses.
- It orbits at about 1.16 AU from its host star.
- The host ultracool dwarf has a mass around 0.078 solar masses.

## Abstract

We combine $Spitzer$ and ground-based KMTNet microlensing observations to identify and precisely measure an Earth-mass ($1.43^{+0.45}_{-0.32} M_\oplus$) planet OGLE-2016-BLG-1195Lb at $1.16^{+0.16}_{-0.13}$ AU orbiting a $0.078^{+0.016}_{-0.012} M_\odot$ 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.