Atmospheric implications of the lack of H3+ detection at Neptune

Moore, L., Moses, J. I., Melin, H., Stallard, T. S. and O'Donoghue, J. ORCID: https://orcid.org/0000-0002-4218-1191 (2020) Atmospheric implications of the lack of H3+ detection at Neptune. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 378 (2187). 20200100. ISSN 1471-2962 doi: 10.1098/rsta.2020.0100

Abstract/Summary

H3+ has been detected at all of the solar system giant planets aside from Neptune. Current observational upper limits imply that there is far less H3+ emission at Neptune than rudimentary modelling would suggest. Here, we explore via modelling a range of atmospheric conditions in order to find some that could be consistent with observational constraints. In particular, we consider that the upper atmosphere might be much cooler than it was during the 1989 Voyager 2 encounter, and we examine the impact of an enhanced influx of external material that could act to reduce H3+ density. Resulting ionosphere models that are consistent with existing H3+ observational constraints have an exospheric temperature of 450K or less, 300K lower than the Voyager 2 value. Alternatively, if a topside CO influx of 2 × 10^8 cm−2 s−1 is imposed, the upper atmospheric temperature can be higher, up to 550 K. The potential cooling of Neptune’s atmosphere is relevant for poorly understood giant planet thermospheric energetics, and would also impact aerobreaking manoeuvers for any future spacecraft. Such a large CO influx, if present, could imply Triton is a very active moon with prominent atmospheric escape, and/or that Neptune’s rings significantly modify its upper atmosphere, and the introduction of so much exogenic material would complicate interpretation of the origin of species observed in Neptune’s lower atmosphere. This article is part a discussion meeting issue ‘Future exploration of ice giant systems’.

Item Type	Article
URI	https://centaur.reading.ac.uk/id/eprint/120078
Identification Number/DOI	10.1098/rsta.2020.0100
Refereed	Yes
Divisions	No Reading authors. Back catalogue items Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Publisher	Royal Society Publishing
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