Though missions such as Kepler, K2, and TESS have discovered >2,000 sub-Neptune and Neptunian planets, there is a dearth of such planets at close-in (P≲3 days) orbits. This feature, called the Neptune desert or the evaporation desert, is believed to be primarily shaped by planetary migration and photoevaporation. However, this region is not completely devoid of planets--a small number of very hot Neptunes reside within the desert. These planets provide an opportunity to directly probe the effects of migration and photoevaporation. We present confirmation of TOI-5800 b, an eccentric sub-Neptune on a ≈2.6 day period that is likely actively undergoing tidal migration. We use radial velocity measurements from the Carnegie Planet Finder Spectrograph (PFS) to constrain TOI-5800 b's mass and eccentricity. We find that it has an unusually high eccentricity (0.39±0.07) for its short orbit. TOI-5800 is therefore currently experiencing high levels of tidal heating as it moves into the desert. Ranked as a top candidate for transmission and emission spectroscopy within its temperature and radius regime, TOI-5800 b is a prime target for atmospheric characterization with JWST. TOI-5800 b presents a unique opportunity to study the atmosphere of a planet undergoing tidal heating and to probe the composition of sub-Neptune planets.
@article{arxiv.2505.10324,
title = {An Eccentric Sub-Neptune Moving Into the Evaporation Desert},
author = {Sydney Jenkins and Andrew Vanderburg and Ritika Sethi and Sarah Millholland and Joseph E. Rodriguez and Luca Fossati and Andreas Krenn and Emily Pass and Alex Venner and Paul Butler and Hugh Osborn and Aaron Householder and Carl Ziegler and Juliette Becker and Perry Berlind and Allyson Bieryla and Christopher Broeg and Michael L. Calkins and Jeffrey D. Crane and Tansu Daylan and Julien de Wit and Jason D. Eastman and David Ehrenreich and Gilbert A. Esquerdo and Michael Fausnaugh and Yadira Gaibor and David W. Latham and Monika Lendl and Andrew W. Mayo and Gaetano Scandariato and Steve Shectman and Stephanie Striegel and Johanna Teske and Thomas G. Wilson},
journal= {arXiv preprint arXiv:2505.10324},
year = {2025}
}