TOI-1075 b: A Dense, Massive, Ultra-Short Period Hot Super-Earth Straddling the Radius Gap

TL;DR

This paper reports the discovery and characterization of TOI-1075 b, an ultra-short period hot super-Earth with high density, providing insights into its composition, formation, and potential for atmospheric studies, contributing to understanding the radius gap in exoplanets.

Contribution

The study presents the first detailed characterization of a dense, ultra-short period hot super-Earth orbiting an M-dwarf, including mass, radius, and density measurements, and discusses its implications for planet formation theories.

Findings

TOI-1075 b has a radius of approximately 1.79 R⊕ and a mass of about 10 M⊕.

The planet's high density suggests a rocky composition with little to no H/He atmosphere.

Radial velocity data indicate a potential additional planet in the system.

Abstract

Populating the exoplanet mass-radius diagram in order to identify the underlying relationship that governs planet composition is driving an interdisciplinary effort within the exoplanet community. The discovery of hot super-Earths - a high temperature, short-period subset of the super-Earth planet population - has presented many unresolved questions concerning the formation, evolution, and composition of rocky planets. We report the discovery of a transiting, ultra-short period hot super-Earth orbiting TOI-1075 (TIC 351601843), a nearby ($d$ = 61.4 pc) late K-/early M-dwarf star, using data from the Transiting Exoplanet Survey Satellite (TESS). The newly discovered planet has a radius of $1.791^{+0.116}_{-0.081}$ $R_{\oplus}$, and an orbital period of 0.605 days (14.5 hours). We precisely measure the planet mass to be $9.95^{+1.36}_{-1.30}$ $M_{\oplus}$ using radial velocity measurements obtained with the Planet Finder Spectrograph (PFS), mounted on the Magellan II telescope. Our radial velocity data also show a long-term trend, suggesting an additional planet in the system. While TOI-1075 b is expected to have a substantial H/He atmosphere given its size relative to the radius gap, its high density ($9.32^{+2.05}_{-1.85}$ $\rm{g/cm^3}$) is likely inconsistent with this possibility. We explore TOI-1075 b's location relative to the M-dwarf radius valley, evaluate the planet's prospects for atmospheric characterization, and discuss potential planet formation mechanisms. Studying the TOI-1075 system in the broader context of ultra-short period planetary systems is necessary for testing planet formation and evolution theories, density enhancing mechanisms, and for future atmospheric and surface characterization studies via emission spectroscopy with JWST.