Yves Langevin

The Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) investigation, on board the European Space Agency Mars Express mission, is mapping the surface composition of Mars at a 0.3- to 5-kilometer resolution by means of visible-near-infrared hyperspectral reflectance imagery. The data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy, offering key insights into the evolution of Mars. OMEGA has identified and mapped mafic iron-bearing silicates of both the northern and southern crust, localized concentrations of hydrated phyllosilicates and sulfates but no carbonates, and ices and frosts with a water-ice composition of the north polar perennial cap, as for the south cap, covered by a thin carbon dioxide-ice veneer.

National audience

Optical properties of lunar surface materials are modified by exposure to the space environment, including bombardment by solar wind particles and micrometeorites. One of the main problems in the interpretation of lunar spectral observations is to separate the effects of exposure (“space weathering”) and those due to the composition of the soils (mainly iron and titanium content). Here we use Clementine near‐infrared (NIR) data to investigate this problem for highland‐type soils in the Tycho crater area. Our approach is based on the methods developed for an analysis of a mare region near Aristarchus Plateau [ Le Mouélic et al. , 2000 ]. We show that the systematic relationships between spectral parameters (1‐μm band depth and continuum slope), which were previously observed in a mare area with varying maturity degree, are also valid for highland‐type soils. This technique aimed at evaluating the iron content of the surface materials from Clementine UV‐visible (UVVIS) and near‐infrared data can therefore be applied globally. This approach complements the widely used method of Lucey and coworkers, which relies on the UV‐visible bands only. The proposed method relies mostly on band ratios. The iron map produced from this method is therefore less dependent on topography than the iron estimates obtained with UV‐visible data alone, where brightness is one of the controlling parameters. Therefore the proposed approach should be particularly useful at middle to high latitudes, where local topography generates large variations in brightness and therefore hampers the interpretation of iron maps produced from UV‐visible bands only.

The Rosetta spacecraft accomplished a flyby of Mars on its way to 67P/Churyumov‐Gerasimenko on 25 February 2007. In this paper we describe the measurements obtained by the M channel of the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS‐M) and the first scientific results derived from their analysis. The broad spectral coverage of the VIRTIS‐M in the IR permitted the study of various phenomena occurring in the Martian atmosphere; observations were further exploited to achieve accurate absolute radiometric calibration. Nighttime data from the VIRTIS‐M constrain the air temperature profile in the lower atmosphere (5–30 km), using variations in CO 2 opacity at 4.3 μ m. A comparison of this data with the global circulation model (GCM) by Forget et al. (1999) shows a trend of slightly higher air temperature in the VIRTIS‐M retrievals; this is accompanied by the presence of moderate decreases (∼5 K) in large sections of the equatorial region. This is potentially related to the occurrence of water ice clouds. Daytime data from the VIRTIS‐M reveal CO 2 non–local thermodynamic equilibrium emission in the high atmosphere. A mapping of emission intensity confirms its strict dependence on solar zenith angle. Additionally, devoted limb observations allowed the retrieval of vertical emission intensity profiles, indicating a peak around 105 km in southern tropical regions. Ozone content can be effectively monitored by the emission of O 2 ( a 1 Δ g ) at 1.27 μ m. Retrieved emission intensity shows that polar regions are particularly rich in ozone. Aerosol scattering was observed in the 1–2.5 μ m region above the night region above the night disk, suggesting the occurrence of very high noctilucent clouds.

International audience