Spectroscopic Exploration of the Martian System
Ann C. Vandaele (1), F. Daerden (1), S. Aoki (2), C. Depiesse (1), J. Erwin (1), L. Neary (1), A. Piccialli (1), S. Robert (1,3), I. R. Thomas (1), L. Trompet (1), S. Viscardy (1), B. Vispoel (1), Y. Willame (1)
(1) Royal Belgian Institute for Space Aeronomy (IASB-BIRA), Brussels, Belgium; (2) ISAS, JAXA, Japan; (3) Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Chemin du Cyclotron 2, 1348 Louvain-la-Neuve, Belgium ()
Mars and its two moons Phobos and Deimos have been scrutinized for decades using spectroscopic instruments operating in different wavelength ranges, at different spectral resolutions. After a brief description of what such instruments can teach us, we will focus on some recent results obtained by the NOMAD (“Nadir and Occultation for MArs Discovery”) spectrometer suite on board the ExoMars Trace Gas Orbiter. This instrument has been designed to investigate the composition of Mars' atmosphere, with a particular focus on trace gases, clouds and dust. The instrument probes the ultraviolet and infrared regions covering large parts of the 0.2-4.3 µm spectral range [1,2], with 3 spectral channels: a solar occultation channel (SO – Solar Occultation; 2.3–4.3 μm), a second infrared channel capable of nadir, solar occultation, and limb sounding (LNO – Limb Nadir and solar Occultation; 2.3–3.8 μm), and an ultraviolet/visible channel (UVIS – Ultraviolet and Visible Spectrometer, 200–650 nm). The infrared channels record spectra at high spectral resolutions (λ/dλ~10,000–20,000) provided by an echelle grating used in combination with an Acousto Optic Tunable Filter (AOTF) which selects the spectral region to be recorded. The sampling rate for the solar occultation measurement is 1 second, which provides high vertical sampling step (~1 km) and resolution (~2 km) from the surface to 200 km. Thanks to the instantaneous change of the observing diffraction orders achieved by the AOTF, the SO channel is able to measure five or six different spectral intervals per second in solar occultation mode. The UVIS channel has a spectral resolution
Since its arrival at Mars in April 2018, NOMAD performed solar occultation, nadir and limb observations dedicated to the determination of the composition and structure of the atmosphere. Since the beginning of operations, NOMAD acquired more than 4000 solar occultations with an almost complete coverage of the planet. Here we report on the different discoveries highlighted by the instrument during its first full Martian year of observations: investigation of the 2018 Global dust storm and its impact on the water uplifting and escape, on temperature and pressure increases within the atmosphere; dust and ice clouds distribution; ozone measurements; dayglow observations; detection of HCl vertical profiles and in general advances in the analysis of the spectra recorded by the three channels of NOMAD.
 Vandaele et al., Planet. Space Sci., 2015, 119, 233-249.
 Vandaele et al., Space Sci. Rev., 2018, 214, 80.