JUICE/SWI measurements of HF and HCl in Earth’s Atmosphere during the Lunar Earth Gravity Assist

The Submillimetre Wave Instrument (SWI) onboard ESA’s JUpiter ICy moons Explorer (JUICE) mission acquired data of the Earth´s atmosphere during the Lunar-Earth Gravity Assist campaign in August 2024. These observations continued for several days after closest approach to investigate performance and test instrument behavior under in-flight conditions. SWI operates simultaneously in two frequency bands, 530–638 GHz and 1066–1286 GHz, with spectral resolution up to 10⁷ provided by its Chirp Transform Spectrometers. During these calibration measurements, several molecular rotational transitions were detected, including those of hydrogen chloride (HCl) and hydrogen fluoride (HF).  

 

In this talk we summarize the context, calibration, and analysis of these data. Using a line-by-line radiative transfer model, we retrieved the abundances of HCl and HF and assess the associated uncertainties. The results are interpreted in the context of stratospheric halogen chemistry: HCl is the principal reservoir species of stratospheric chlorine, while HF is a reservoir species of fluorine (F).  More broadly, these observations provide an important end-to-end validation of SWI’s spectroscopic capabilities and establish a benchmark for future studies of Jupiter’s atmosphere and the exospheres of the Galilean icy moons with JUICE/SWI.

 

Acknowledgements

SWI has been designed and developed by an international consortium of institutes led by the Max Planck Institute for Solar System Research (MPS, Germany) and including the Laboratory for Studies of Radiation and Matter in Astrophysics (LERMA, France), the Space Research Centre of the Polish Academy of Sciences (CBK, Poland), Chalmers University of Technology (Sweden), the Institute of Applied Physics of the University of Bern (IAP, Switzerland), the National Institute of Information and Communications Technology (NICT, Japan) and the French Space Agency CNES with additional support from the Laboratoire d’Instrumentation et de Recherche en Astrophysique of the Observatoire de Paris (LIRA, France), the Laboratoire d’Astrophysique de Bordeaux (LAB, France), the RPG Radiometer Physics GmbH (Germany), and Omnisys Instrument AV (Sweden). This development has been supported by national funding agencies and other organizations, including the Deutsches Zentrum für Luft- und Raumfahrt (DLR) and by central resources of the Max-Planck-Society. R. Moreno, and T. Cavalié acknowledge funding from the Centre National d’Études Spatiales (CNES).  Juice is a mission under ESA leadership with contributions from its Member States, NASA, JAXA, and the Israel Space Agency. It is the first Large-class mission in ESA’s Cosmic Vision Program.