HARPS-N reveals the Secrets of the Hot Neptune TOI-3862 b
Thanks to observations carried out with the high resolution spectrograph HARPS-N at the Telescopio Nazionale Galileo (TNG), astronomers have characterized the rare exoplanet named TOI-3862 b. The planet, with a radius of approximately 0.8 Jupiter radii and an unusually high density of ~ 1.7 g cm-3, resides in the so-called hot Neptune desert, a region where Neptune-sized planets are scarce despite their relative detectability.
TOI-3862 b was first identified through transit observations by space-based missions, including the satellite TESS. Its orbital period is extremely short, just 1.56 days, around a solar-type star. The combination of high mass, high density, and strong stellar irradiation makes it an ideal laboratory for studying atmospheric loss mechanisms, including photoevaporation and tidal heating, as well as for testing scenarios of early orbital migration versus the stripping of a more massive gas giant.
The planet's mass and density were precisely determined through radial-velocity measurements performed entirely with HARPS-N.
"These observations strongly highlight the central role of the TNG in advancing the detailed study of extrasolar planetary systems" comments Ilaria Carleo researcher at INAF and first author of the paper, "underscoring its importance as a key facility for the community and its important contribution in providing high-resolution spectroscopy that complements space-based transit surveys."
TOI-3862_RVs-1: HARPS-N RV data for TOI-3862, with the 1p+GP model overplotted. More information in the paper.
Planet radius vs. orbital period for all known exoplanets, highlighting the hot Neptune desert, ridge, and savanna derived by Castro-González et al. 2024a. The arrows represent the evolution of the planet' radius from the initial value to the current value. More information in the paper.
Link to the paper: https://arxiv.org/abs/2601.10450