An Earth-Mass Planet and a Brown Dwarf in Orbit Around a White Dwarf

TL;DR

This paper reports the discovery of an Earth-mass planet and a brown dwarf orbiting a white dwarf, providing evidence for planetary survival through stellar evolution and insights into future planetary system dynamics.

Contribution

It presents the first evidence of an Earth-mass planet and a brown dwarf orbiting a white dwarf, based on microlensing observations and system evolutionary analysis.

Findings

Earth-mass planet at 2.1 au from the white dwarf

Brown dwarf companion at 22 au, likely evolved from an initial 1 au orbit

Supports planetary survival during stellar evolution

Abstract

Terrestrial planets born beyond 1-3 AU have been theorized to avoid being engulfed during the red-giant phases of their host stars. Nevertheless, only a few gas-giant planets have been observed around white dwarfs (WDs) -- the end product left behind by a red giant. Here we report on evidence that the lens system that produced the microlensing event KMT-2020-BLG-0414 is composed of a WD orbited by an Earth-mass planet and a brown dwarf (BD) companion, as shown by the non-detection of the lens flux using Keck Adaptive Optics (AO). From microlensing orbital motion constraints, we determine the planet to be a $1.9\pm0.2$ Earth-mass ($M_\oplus$) planet at a physical separation of $2.1\pm0.2$ au from the WD during the event. By considering the system evolutionary history, we determine the BD companion to have a projected separation of 22 au from the WD, and reject an alternative model that places the BD at 0.2 au. Given planetary orbital expansion during the final evolutionary stages of the host star, this Earth-mass planet may have existed in an initial orbit close to 1 au, thereby offering a glimpse into the possible survival of planet Earth in the distant future.