A Headwind-like Helium Outflow from TOI-3884b
Abstract
Constraining atmospheric loss is crucial for understanding the evolution of planetary atmospheres. We report the detection of an evaporating exosphere from TOI-3884b, a super-Neptune in a polar orbit around an M4 dwarf star. We infer this evaporation from a 6.8±0.27\% excess transit depth in the He I 10830 Å\, line, observed during five transits of TOI-3884b with the Habitable Zone Planet Finder spectrometer. While we observe outflow signatures starting as early as 5 hours before the onset of the planet's optical transit, no significant post-transit tail is detected. Hitherto, such a pre-transit headwind without a significant post-transit tail has only been detected from HAT-P-67b, a hot Saturn orbiting an F-type star. This asymmetric outflow morphology supports irradiation-driven mass loss over core-heated mass loss, and we explore whether this could be caused by sub-Alfvén star-planet interaction. The detection of such complex outflow morphologies is now opening a new window, enabling us to test theories of star-planet interactions and planetary magnetic fields with observations.
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BibTeX
@misc{ninan2026headwindlike,
title = {{A Headwind-like Helium Outflow from TOI-3884b}},
author = {Joe P. Ninan and Jessica Libby-Roberts and Suvrath Mahadevan and Oleg Kochukhov and Daniel M. Krolikowski and Gudmundur Stefansson and Shubham Kanodia and Jaume Orell-Miquel and Caroline V. Morley and Kevin France and Girish Duvvuri and Chad F. Bender and William D. Cochran and Megan Delamer and Scott A. Diddams and Samuel Halverson and Fred Hearty and Leslie Hebb and Andrew Monson and Paul Robertson and Arpita Roy and Christian Schwab},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.31492},
eprint = {2610.31492},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.31492},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A Headwind-like Helium Outflow from TOI-3884b
AU - Joe P. Ninan
AU - Jessica Libby-Roberts
AU - Suvrath Mahadevan
AU - Oleg Kochukhov
AU - Daniel M. Krolikowski
AU - Gudmundur Stefansson
AU - Shubham Kanodia
AU - Jaume Orell-Miquel
AU - Caroline V. Morley
AU - Kevin France
AU - Girish Duvvuri
AU - Chad F. Bender
AU - William D. Cochran
AU - Megan Delamer
AU - Scott A. Diddams
AU - Samuel Halverson
AU - Fred Hearty
AU - Leslie Hebb
AU - Andrew Monson
AU - Paul Robertson
AU - Arpita Roy
AU - Christian Schwab
PY - 2026
DA - 2026/10/22
PB - arXiv
DO - 10.48550/arxiv.2610.31492
UR - https://arxiv.org/abs/2610.31492
AB - Constraining atmospheric loss is crucial for understanding the evolution of planetary atmospheres. We report the detection of an evaporating exosphere from TOI-3884b, a super-Neptune in a polar orbit around an M4 dwarf star. We infer this evaporation from a 6.8±0.27\% excess transit depth in the He I 10830 Å\, line, observed during five transits of TOI-3884b with the Habitable Zone Planet Finder spectrometer. While we observe outflow signatures starting as early as 5 hours before the onset of the planet's optical transit, no significant post-transit tail is detected. Hitherto, such a pre-transit headwind without a significant post-transit tail has only been detected from HAT-P-67b, a hot Saturn orbiting an F-type star. This asymmetric outflow morphology supports irradiation-driven mass loss over core-heated mass loss, and we explore whether this could be caused by sub-Alfvén star-planet interaction. The detection of such complex outflow morphologies is now opening a new window, enabling us to test theories of star-planet interactions and planetary magnetic fields with observations.
ER -