JWST observations of exogenic species on Jupiter: HCN, H₂O, and CO₂

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris-Cité, Meudon, France
² Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, Pessac 33615, France
³ School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
⁴ Aix-Marseille Université, CNRS, CNES, Institut Origines, LAM, Marseille, France
⁵ Laboratory for Planetary and Atmospheric Physics, STAR Institute, University of Liège, Liège, Belgium
⁶ Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA
⁷ Department of Astronomy, University of California, Berkeley, CA 94720, USA

^★ Corresponding author; pablo.ovalle@obspm.fr

Received: 21 December 2024
Accepted: 19 March 2025

Abstract

Context. The impact of the Shoemaker-Levy 9 (SL9) comet on Jupiter in 1994 opened up a new field of study focused on the exogenic species within Jupiter’s atmosphere. Among these species, we find H₂O, CO, and HCN. It is thought that these species coexist at the same pressure level (∼3 mbar in 2022) and that the interaction between some of them creates daughter molecules such as CO₂. However, understanding their complex meridional distributions is still a matter of debate.

Aims. We measured the meridional distribution of H₂O, HCN, and CO₂ to understand the chemistry and dynamics leading to these distributions.

Methods. We used James Webb Space Telescope (JWST) Mid InfraRed Instrument (MIRI) medium-resolution spectroscopy observations from 17^∘S to 26^∘S, and from 45^∘S towards the south pole for CO₂, H₂O, and HCN. We used a radiative transfer code coupled with an inversion algorithm to retrieve the temperature using the CH₄ v₄ band and the abundance of the species for the different latitudes.

Results. We found an increase in H₂O in the south polar region, while CO₂ is found to be depleted, which points towards an exchange of oxygen between H₂O and CO₂ happening in the southern auroral region. The HCN abundance decreases towards the pole, and abundance values are similar to the ones obtained with ALMA in 2017. The depletion of HCN may be due to heterogeneous chemistry related to stratospheric polar aerosols.

Conclusions. The exogenic molecules analysed seem to be influenced either by polar aerosols produced by ion-neutral chemistry (e.g. HCN) or by particle precipitation occurring in the auroral regions (e.g. H₂O and CO₂). These measurements provide new insights into chemical evolution at a small spatial scale, revealing previously undetected localized trends.