GJ 367b: A dense ultra-short period sub-Earth planet transiting a nearby red dwarf star

TL;DR

This paper reports the discovery and detailed characterization of GJ 367b, an ultra-short-period sub-Earth exoplanet with a dense, iron-rich composition orbiting a nearby red dwarf star.

Contribution

It provides precise measurements of GJ 367b's mass, radius, and density, offering insights into its interior structure and formation, which are novel for such ultra-short-period sub-Earth planets.

Findings

GJ 367b has a radius of 0.718 Earth radii.

GJ 367b has a mass of 0.546 Earth masses.

The planet's density suggests an iron-rich interior similar to Mercury.

Abstract

Ultra-short-period (USP) exoplanets have orbital periods shorter than one day. Precise masses and radii of USPs could provide constraints on their unknown formation and evolution processes. We report the detection and characterization of the USP planet GJ 367b using high precision photometry and radial velocity observations. GJ 367b orbits a bright (V-band magnitude = 10.2), nearby, red (M-type) dwarf star every 7.7 hours. GJ 367b has a radius of $0.718 \pm 0.054$ Earth-radii, a mass of $0.546 \pm 0.078$ Earth-masses, making it a sub-Earth. The corresponding bulk density is $8.106 \pm 2.165$ g cm$^-3$, close to that of iron. An interior structure model predicts the planet has an iron core radius fraction of $86 \pm 5\%$, similar to Mercury's interior.