Stratospheric aerosols and C₆H₆ in Jupiter’s south polar region from JWST/MIRI observations

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris-Cité, Meudon, France
² Laboratoire de Météorologie Dynamique/Institut Pierre-Simon Laplace (LMD/IPSL), Sorbonne Université, CNRS, École Polytechnique, Institut Polytechnique de Paris, École Normale Supérieure (ENS), PSL Research University, Paris, France
³ School of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
⁴ Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, Pessac 33615, France
⁵ Aix-Marseille Université, CNRS, CNES, Institut Origines, LAM, Marseille, France
⁶ Instituto de Astrofísica de Andalucía, Consejo Superior de Investigaciones Científicas (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁷ Escuela de Ingeniería de Bilbao, Universidad del País Vasco, UPV/EHU, Bilbao, Spain
⁸ Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA
⁹ Department of Astronomy, University of California, Berkeley, CA 94720, USA
¹⁰ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹¹ Association of Universities for Research in Astronomy, Washington, DC, 20004, USA
¹² NASA Goddard Space Flight Center, Astrochemistry Laboratory, Greenbelt MD 20771, USA

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

Received: 11 July 2024
Accepted: 13 September 2024

Abstract

Context. The polar atmosphere of Jupiter is significantly affected by auroral activity, which can induce both thermal and chemical differences compared to the rest of the atmosphere. In particular, auroral activity enhances the production of various hydrocarbons, including benzene. Benzene could be a potential precursor to the formation of the stratospheric hazes.

Aims. We investigated the spatial distribution of the benzene abundance across latitudes ranging from 50°S to 81°S and 17°S to 25°S. Additionally, we examined the chemical origin of polar aerosols and their latitudinal distribution.

Methods. We employed James Webb Space Telescope (JWST) Mid InfraRed Instrument (MIRI) observations to measure the benzene abundance based on its emission at 674 cm⁻¹. Additionally, we examined the spectral dependence of the aerosol opacity within the 680–760 and 1380–1500 cm⁻¹ spectral ranges, and mapped their distribution from 80°S–50°S.

Results. At latitudes lower than 60°S, benzene is found to be up to ten times more abundant compared to lower latitudes. This enhancement of C₆H₆ is well mixed longitudinally and not particularly concentrated inside the auroral oval. Photochemical models predict a decrease in the abundance as we approach the mid latitudes, but fail at polar latitudes as they do not include ion-neutral chemistry. Moreover, we find that the southern polar atmosphere is enriched with aerosols at ~10 mbar. The optical depth of the aerosols increases at latitudes poleward of ~60°S, similar to the enhancement of C₆H₆. These aerosols have spectral features similar to the aerosols of Titan and Saturn, and the mass loading is of ~1.2 ± 0.2 × 10⁻⁴ g cm⁻². Finally, we quantified the impact of these aerosols on the retrieved temperature structure, causing a decrease in the temperature at pressure levels deeper than 10 mbar.

Conclusions. We find that the auroral precipitation produces abundant stratospheric aerosols, which must play an important role in the chemistry and dynamics of the planet.