TOI-2498 b: a hot bloated super-Neptune within the Neptune desert

Abstract

We present the discovery and confirmation of a transiting hot bloated super-Neptune using photometry from the Transiting Exoplanet Survey Satellite (TESS) and the Las Cumbres Observatory Global Telescope (LCOGT) and radial velocity measurements from the High Accuracy Radial velocity Planet Searcher (HARPS). The host star TOI-2498 is a V = 11.2, G-type (Teff = 5905 ± 12 K) solar-like star with a mass of 1.12 ± 0.02 M⊙ and a radius of 1.26 ± 0.04 R⊙. The planet, TOI-2498 b, orbits the star with a period of 3.7 d, has a radius of 6.1 ± 0.3 R⊕, and a mass of 35 ± 4 M⊕. This results in a density of 0.86 ± 0.25 g cm-3. TOI-2498 b resides on the edge of the Neptune desert; a region of mass-period parameter space in which there appears to be a dearth of planets. Therefore TOI-2498 b is an interesting case to study to further understand the origins and boundaries of the Neptune desert. Through modelling the evaporation history, we determine that over its ∼3.6 Gyr lifespan, TOI-2498 b has likely reduced from a Saturn-sized planet to its current radius through photoevaporation. Moreover, TOI-2498 b is a potential candidate for future atmospheric studies searching for species like water or sodium in the optical using high resolution spectroscopy, and for carbon-based molecules in the infrared using JWST.