Transport processes of dust and water in the Martian atmosphere revealed by the MIRS: an imaging spectrometer for the MMX mission
Résumé
The MMX infrared spectrometer (MIRS) is an imaging spectrometer onboard MMX JAXA mission. MMX (Martian Moon eXploration) (Kuramoto et al. 2022, EPS 74, 12) is scheduled to be launched in 2024 with sample return from Phobos to Earth in 2029. MIRS will remotely provide near-infrared (IR) spectral maps in the spectral range from 0.9 to 3.6 micron with a spectral resolution better than 20 nm for Martian atmosphere, in addition to those of Phobos and Deimos (see Barucci et al., in the section B1.1). The previous observations of the lower atmosphere have been mostly done by polar-orbiting spacecrafts, such as Mars Global Surveyor (MGS), Mars Express (MEX), and Mars Reconnaissance Orbiter (MRO). These observations have provided global pictures of the atmospheric species and aerosols distributions at the Martian atmosphere at (mostly) fixed local times. Thus, development and decay of mesoscale to synoptic scale atmospheric events (such as horizontal water transport including surface-atmosphere interaction, clouds formation, and dust storms, etc.) have remained unclear. The more recent TGO mission already improved this coverage with its inclined orbit (74 degree) allowing different local times to be probed but still limited. The equatorial orbit of MMX can offer some advantages for global mapping of the Martian atmosphere. Being placed on the same orbit as Phobos around Mars, at altitudes ~ 6000 km, the spacecraft will have a ~7 hr orbit around Mars, allowing to complete a global mapping of Mars. The well-controlled scanner system of MIRS enables the specific pointing of the instrument, thus allowing MIRS measurements to obtain wide spatial coverage in hourly time-scale. The spacecraft's slewing capabilities will also be used during observations of Mars in order to maximize the coverage of the MIRS from low to mid-latitudes within an hour, or to obtain almost global mapping of the sunlit hemisphere with several orbits, in combination with its scanner. These provide the first opportunity to follow the temporal evolution of the atmospheric species (CO2, H2O, CO) and aerosols (dust and clouds) with a mesoscale spatial resolution to reveal the rapid transport processes of the atmospheric species and aerosols with relatively high spatial resolution (typically 2-5 km). Such time-resolved pictures of the atmospheric phenomena should be an important clue to understand both the processes of water exchange between the surface/underground reservoirs and the atmosphere and the drivers of efficient material transport to the upper atmosphere.