Journal article
Uranus and Neptune’s stratospheric water abundance and vertical profile from Herschel-HIFI
- Abstract:
- Here we present new constraints on Uranus’s and Neptune’s externally sourced stratospheric water abundance using disk-averaged observations of the 557 GHz emission line from Herschel’s Heterodyne Instrument for the Far-Infrared. Derived stratospheric column water abundances are × 1014 cm−2 for Uranus and ×1014 cm−2 for Neptune, consistent with previous determinations using ISO-SWS and Herschel-PACS. For Uranus, excellent observational fits are obtained by scaling photochemical model profiles or with step-type profiles with water vapor limited to ≤0.6 mbar. However, Uranus’s cold stratospheric temperatures imply a ∼0.03 mbar condensation level, which further limits water vapor to pressures ≤0.03 mbar. Neptune’s warmer stratosphere has a deeper ∼1 mbar condensation level, so emission-line pressure broadening can be used to further constrain the water profile. For Neptune, excellent fits are obtained using step-type profiles with cutoffs of ∼0.3–0.6 mbar or by scaling a photochemical model profile. Step-type profiles with cutoffs ≥1.0 mbar or ≤0.1 mbar can be rejected with 4σ significance. Rescaling photochemical model profiles from Moses & Poppe to match our observed column abundances implies similar external water fluxes for both planets: × 104 cm−2 s−1 for Uranus and ×104 cm−2 s−1 for Neptune. This suggests that Neptune’s ∼4 times greater observed water column abundance is primarily caused by its warmer stratosphere preventing loss by condensation, rather than by a significantly more intense external source. To reconcile these water fluxes with other stratospheric oxygen species (CO and CO2) requires either a significant CO component in interplanetary dust particles (Uranus) or contributions from cometary impacts (Uranus, Neptune)
- Publication status:
- Published
- Peer review status:
- Peer reviewed
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(Preview, Version of record, 1.2MB, Terms of use)
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- Publisher copy:
- 10.3847/PSJ/ac650f
Authors
- Publisher:
- IOP Publishing
- Journal:
- Planetary Science Journal More from this journal
- Volume:
- 3
- Issue:
- 4
- Article number:
- 96
- Publication date:
- 2022-04-29
- Acceptance date:
- 2022-04-05
- DOI:
- EISSN:
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2632-3338
- Language:
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English
- Keywords:
- Pubs id:
-
1249555
- Local pid:
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pubs:1249555
- Deposit date:
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2022-04-06
Terms of use
- Copyright holder:
- Teanby et al.
- Copyright date:
- 2022
- Rights statement:
- © 2022. 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.
- Licence:
- CC Attribution (CC BY)
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