TOI-1075 b: The Densest Ultra-Short Period Hot Super-Earth Straddling the Radius Gap

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. Hot super-Earths – a high temperature, short-period subset of the super-Earth planet population – represent a readily accessible population that can be used to address 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 = 61.5 pc) late K/early M dwarf star, using data from the Transiting Exoplanet Survey Satellite (TESS). The newly discovered planet has a radius of 1.79+0.12–0.08 REarth, and an orbital period of 0.605 days (14.5 hours). Radial velocity measurements using the Planet Finder Spectrograph (PFS), mounted on the Magellan II telescope, confirm the existence of the planet, and we precisely measure the planet mass to be 9.95+1.36–1.30 MEarth. Our radial velocity data show a long-term trend, suggesting an additional planet in the system. TOI-1075 b’s mean density is ~9.32 g/cm3, making it almost twice as dense as the Earth, with a composition expected to be significantly enriched in iron. TOI-1075 b is the densest high temperature, ultra-short period planet above the radius gap discovered to date, making the system ideal for testing planet formation processes and evolution theories. Additionally, we evaluate the planet for future atmospheric characterization studies