Chasing the Martian Aerosols with the Upcoming MIRS/MMX instrument

          MMX InfraRed Spectrometer (MIRS) is the push-broom imaging spectrometer [1] aboard the Martian Moons eXploration (MMX) mission [2] by JAXA, operating between 0.9 and 3.6 µm with a spectral resolution of around 22 nm below 3.2 µm. The mission will be launched in autumn 2026 to the Martian system, with an arrival planned for 2027. The main objective of the mission is to study the two Martian moons, Phobos and Deimos, and to collect samples from Phobos to bring back to Earth in 2031. Another major aim of the mission [3] and the MIRS instrument [1] is to answer key science questions on the transport processes of dust and water in the Martian atmosphere [3], such as: how do local and regional dust storms form, grow and evolve? What is the diurnal behaviour of water ice clouds (formation, transport, dynamics)?

          The MMX probe will be injected into a quasi-circular equatorial orbit around Mars at an altitude of about 6000 km. From this particular orbit, four different observation modes of MIRS are expected for Mars observations: nominal mode maximising the longitudinal overlap, global mapping mode covering all the illuminated Martian disk up to medium-high latitudes (+/- 60°), region of interest mode providing temporal resolution (down to 15 minutes) above a limited area, and the limb mode. Each mode will be useful to study the spatial and temporal variations of aerosols (atmospheric dust, water and CO₂ ices), and their fine diurnal variations. Indeed, the particular orbit of MMX (the second probe after the Emirates Mars Mission to be in equatorial orbit near Mars) will give us access to observations at very different local times with high spatial resolution, which will certainly provide some answers to the question addressed above.

          The objective is to develop a pipeline that will invert flight data to extract aerosol properties (e.g., optical depths, particle sizes) as fast as the data is downloaded. To do so, different existing retrieval methods will be implemented, such as the dust optical depth retrievals at 2 µm [4] and 2.77 µm [5]. These recently developed methods are based on CO₂ absorption band variations due to atmospheric dust, allowing to retrieve automatically dust optical depth on near-IR nadir observations. We are also developing a more usual method based on the spectral continuum variations induced by the aerosols, for which we are building a look-up table based on simulated spectra. We will present an update on these aerosol inversion methods and also on the Mars observation strategy.

Acknowledgments:
We thank the MMX JAXA teams for their efforts and CNES for the financial support and collaboration to build the MIRS instrument.

References:
[1] Barucci M. A. et al. (2021) Earth, Plan. and Space, 73, 211. [2] Kuramoto K. et al. (2022) Earth, Plan. and Space, 74, 12. [3] Ogohara K. et al. (2021) Earth, Plan. and Space, 74, 1. [4] Leseigneur Y. and Vincendon M. (2023) Icarus, 392, 115366. [5] Kazama A. et al. (2025) JGR: Planets, 130, E2025JE008987.