Does Cumulative XUV Unify the Neptunian Desert?
Abstract
The Neptunian desert is the scarcity of roughly $2−10\,R_{\oplus}$ planets on orbits of a few days. Atmospheric escape driven by stellar X-rays and extreme-ultraviolet (XUV) radiation may shape its lower boundary by stripping hydrogen-helium envelopes. Because M dwarfs and F-, G-, and K-type stars have different activity histories, present bolometric irradiation may not trace the cumulative high-energy dose that drives escape. We ask whether cumulative XUV yields a common boundary across spectral type and whether the convergence survives star-to-star variation in age and rotation. Using 1850 Kepler and TESS planets, Model for Rotation of Stars (MORS) activity tracks, and a global boundary model, we find that the offset between M dwarfs and FGK stars shrinks from −1.065 dex in bolometric flux to −0.369 dex for a common 5 Gyr median-rotation XUV history. Assigning plausible ages and initial rotations to individual hosts preserves the smaller XUV offset in every trial, with a median reduction of 69.1%. A common-period null yields comparable alignment. Cumulative XUV therefore substantially reduces the host-type dependence, but the present data do not establish a universal XUV threshold independent of orbital period.
Related
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BibTeX
@misc{jiang2026does,
title = {{Does Cumulative XUV Unify the Neptunian Desert?}},
author = {Qunfeng Jiang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.21285},
eprint = {2608.21285},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.21285},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Does Cumulative XUV Unify the Neptunian Desert?
AU - Qunfeng Jiang
PY - 2026
DA - 2026/10/10
PB - arXiv
DO - 10.48550/arxiv.2608.21285
UR - https://arxiv.org/abs/2608.21285
AB - The Neptunian desert is the scarcity of roughly $2−10\,R_{\oplus}$ planets on orbits of a few days. Atmospheric escape driven by stellar X-rays and extreme-ultraviolet (XUV) radiation may shape its lower boundary by stripping hydrogen-helium envelopes. Because M dwarfs and F-, G-, and K-type stars have different activity histories, present bolometric irradiation may not trace the cumulative high-energy dose that drives escape. We ask whether cumulative XUV yields a common boundary across spectral type and whether the convergence survives star-to-star variation in age and rotation. Using 1850 Kepler and TESS planets, Model for Rotation of Stars (MORS) activity tracks, and a global boundary model, we find that the offset between M dwarfs and FGK stars shrinks from −1.065 dex in bolometric flux to −0.369 dex for a common 5 Gyr median-rotation XUV history. Assigning plausible ages and initial rotations to individual hosts preserves the smaller XUV offset in every trial, with a median reduction of 69.1%. A common-period null yields comparable alignment. Cumulative XUV therefore substantially reduces the host-type dependence, but the present data do not establish a universal XUV threshold independent of orbital period.
ER -