Quantified Estimation of Molecular Detections across Different Classes of Neptunian Atmospheres Using Cross-correlation Spectroscopy: Prospects for Future Extremely Large Telescopes with High-resolution Spectrographs
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1.
Ludwig-Maximilians-Universität München
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2.
Excellence Cluster Universe
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3.
National Institute of Science Education and Research
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4.
Homi Bhabha National Institute
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5.
California Institute of Technology
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6.
Jet Propulsion Lab
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7.
Max Planck Institute for Astronomy
Abstract
Neptune-size exoplanets are less studied as characterizing their atmospheres presents challenges due to their relatively small radius and atmospheric scale height. As the most common outcome of planet formation, these planets are crucial for understanding planetary formation, migration theories, atmospheric composition, and potential habitability. Their diverse atmospheres, influenced by equilibrium temperature, composition, and cloud presence, offer unique opportunities to study atmospheric dynamics and chemistry. While low-resolution spectroscopy struggles with atmospheric characterization due to clouds, high-resolution observations provide detailed analysis of the atmospheres by detecting molecular lines beyond the cloud deck. This study investigates four subclasses of Neptune atmospheres: HAT-P-11 b (warm Neptune), HD 63433c (warm sub-Neptune), K2-25 b (temperate Neptune), and TOI-270 d (temperate sub-Neptune), using six ground-based spectrographs: GIANO-B, CARMENES, IGRINS, HISPEC, MODHIS, and ANDES over one and three transits. Our simulation integrates the chemical kinetics model VULCAN with the 1D line-by-line radiative transfer model petitRADTRANS, and estimates detection significance using the ground-based noise simulator SPECTR. We aim to predict how future extremely large telescopes (ELTs) such as TMT (MODHIS) and E-ELT (ANDES) can utilize their higher resolving powers and larger collecting areas to surpass current observatories in detecting molecular bands. We highlight the importance of photochemistry in these atmospheres and demonstrate how ELTs will help further in constraining nitrogen and sulfur chemistry. Finally, we present a comprehensive picture of cloud presence in the atmospheres and its impact on molecular detectability in Neptune-class atmospheres.
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
L.M. acknowledges financial support from the DAE and DST-SERB research grants [MTR/2021/000864] of the Government of India. D.D. and L.M. thank Dr. Paul Mollière for providing access to petitCODE and for actively participating in discussions regarding its use and applications in the past. D.D. and L.M. thank Mr. Spandan Dash from the University of Warwick for valuable discussions regarding the observational aspects of high-resolution cross-correlation spectroscopy. D.D. and L.M. also thank Prof. Sergey Yurchenko from UCL for his suggestions on generating high-resolution opacities using the ExoCross package. D.D. and L.M. both thank Dr. Miles Currie from NASA GSFC for making the SPECTR simulator available to the community. This research was carried out, in part, at the Jet Propulsion Laboratory and the California Institute of Technology under a contract with the National Aeronautics and Space Administration. The high-resolution opacity files generated in this work will be made available on the petitRADTRANS website in the future. We would like to thank the anonymous referee for constructive comments that helped improve the manuscript.
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Additional details
- Department of Atomic Energy
- Science and Engineering Research Board
- MTR/2021/000864
- Available
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2025-04-29Published online
- Caltech groups
- Division of Physics, Mathematics and Astronomy (PMA), Division of Geological and Planetary Sciences (GPS), Infrared Processing and Analysis Center (IPAC)
- Publication Status
- Published