Stringent Upper Bounds on Atmospheric Mass Loss from Three Neptune-sized Planets in the TOI-4010 System
Creators
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1.
California Institute of Technology
- 2. Carnegie Science Observatories
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3.
University of Chicago
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4.
Imperial College London
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5.
University of Warwick
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6.
University of British Columbia
Abstract
Photoevaporative models predict that the lower edge of the Neptune desert is sculpted by atmospheric mass loss. However, the stellar high-energy fluxes that power hydrodynamic escape and set predicted mass loss rates can be uncertain by multiple orders of magnitude. These uncertainties can be bypassed by studying mass loss for planets within the same system, as they have effectively undergone scaled versions of the same irradiation history. The TOI-4010 system is an ideal test case for mass loss models, as it contains three Neptune-sized planets with planet b located in the “Neptune desert,” planet c in the “Neptune ridge,” and planet d in the “Neptune savanna.” Using Keck/NIRSPEC, we measured the metastable helium transit depths of all three planets in order to search for evidence of atmospheric escape. We place upper bounds on the excess helium absorption of 1.23%, 0.81%, and 0.87% at 95% confidence for TOI-4010 b, c, and d respectively. We fit our transmission spectra with Parker wind models and find that this corresponds to 95th-percentile upper limits of 1010.17 g s−1, 1010.53 g s−1, and 1010.50 g s−1 on the mass loss rates of TOI-4010 b, c, and d respectively. Our non-detections are inconsistent with expectations from one-dimensional hydrodynamic models for solar composition atmospheres. We consider potential reductions in signal from a decreased host star extreme ultra-violet and X-ray luminosity, planetary magnetic fields, enhanced atmospheric metallicities, and fractionation, and explore the implications of our measurements for the past evaporation histories of all three planets.
Copyright and License
© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This research also made use of nep-des (available in https://github.com/castro-gzlz/nep-des). This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under grant No. DGE-1745301. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
We thank the Keck Observatory telescope and support astronomers, with special thanks to Greg Doppmann, Percy Gomez, Anthony Connors, Arina Rostopchina, and John Pelletier. We thank Justin Moore for his significant help in debugging software issues.
Co-author M.Z. thanks the Heising-Simons Foundation for funding his 51 Pegasi b postdoctoral fellowship. Co-author J.F.F. acknowledges studentship support from the UK Science and Technology Facilities Council (STFC) and co-author P.J.W. acknowledges STFC support under consolidated grants ST/T000406/1 and ST/X001121/1.
Facilities
ADS - , NASA Exoplanet Archive - , Keck II/NIRSPEC - .
Software References
AIOLOS (M. Schulik & R. A. Booth 2023), arviz (R. Kumar et al. 2019), astropy (Astropy Collaboration et al. 2013, 2018, 2022), emcee (D. Foreman-Mackey et al. 2013), matplotlib (J. D. Hunter 2007), numpy (C. R. Harris et al. 2020), photoevolver (J. Fernández Fernández et al. 2023), p-winds (L. A. Dos Santos et al. 2022), pyTPCI (R. Rosener et al. 2025), scipy (P. Virtanen et al. 2020).
Files
Saidel_2025_AJ_170_247.pdf
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Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2508.21166 (arXiv)
- Is supplemented by
- Software: https://github.com/castro-gzlz/nep-des (URL)
Funding
- National Science Foundation
- DGE-1745301
- Heising-Simons Foundation
- 51 Pegasi b Postdoctoral Fellowship -
- Science and Technology Facilities Council
- ST/T000406/1
- Science and Technology Facilities Council
- ST/X001121/1
Dates
- Accepted
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2025-08-20
- Available
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2025-09-30Published online