Impact of the transport of magnetospheric electrons on the composition of the Triton atmosphere

¹ Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, Allée Geoffroy Saint-Hilaire, 33615 Pessac, France
e-mail: benjamin.benne@ed.ac.uk
² The University of Edinburgh, School of Geosciences, Edinburgh, UK
³ Laboratoire de Physique Atmosphérique et Planétaire, B5C Quartier Agora, Allée du Six Août 19c, 4000 Liège, Belgium
⁴ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
⁵ Institut des Sciences Moléculaires, CNRS, Univ. Bordeaux, 351 Cours de la Libération, 33400 Talence, France
⁶ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France

Received: 19 April 2023
Accepted: 23 February 2024

Abstract

Context. Due to its inclined orbit and the complex geometry of the magnetic field of Neptune, Triton experiences a highly variable magnetic environment. As precipitation of magnetospheric electrons is thought to have a large impact on the Triton atmosphere, a better understanding of the interaction between its atmosphere and the magnetosphere of Neptune is important.

Aims. We aim to couple a model of the Triton atmosphere with an electron transport model to compute the impact of a varying electron precipitation on the atmospheric composition.

Methods. We coupled a recent photochemical model of the Triton atmosphere with the electron transport model TRANSPlanets. The inputs of this code were determined from Voyager 2 observations and previous studies. The main inputs were the electron precipitation flux, the orbital scaling factor, and the magnetic field strength. The electron-impact ionization and electron-impact dissociation rates computed by TRANSPlanets were then used in the photochemical model. We also analyzed the model uncertainties.

Results. The coupling of the two models enabled us to find an electron density profile, as well as N₂ and N number densities, that are consistent with the Voyager 2 observations. We found that photoionization and electron-impact ionization are of the same order, in contrast to the results of previous photochemical models. However, we emphasize that this result depends on the hypotheses we used to determine the input variables of TRANSPlanets. Our model would greatly benefit from new measurements of the magnetic environment of Triton, as well as of the electron fluxes in the Neptune magnetosphere.