Martian dust storm impact on atmospheric H₂O and D/H observed by ExoMars Trace Gas Orbiter

Global dust storms on Mars are rare but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere, primarily owing to solar heating of the dust. In turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on Mars. Recent observations of the water vapour abundance in the Martian atmosphere during dust storm conditions revealed a high-altitude increase in atmospheric water vapour that was more pronounced at high northern latitudes, as well as a decrease in the water column at low latitudes. Here we present concurrent, high-resolution measurements of dust, water and semiheavy water (HDO) at the onset of a global dust storm, obtained by the NOMAD and ACS instruments onboard the ExoMars Trace Gas Orbiter. We report the vertical distribution of the HDO/H O ratio (D/H) from the planetary boundary layer up to an altitude of 80 kilometres. Our findings suggest that before the onset of the dust storm, HDO abundances were reduced to levels below detectability at altitudes above 40 kilometres. This decrease in HDO coincided with the presence of water-ice clouds. During the storm, an increase in the abundance of H2O and HDO was observed at altitudes between 40 and 80 kilometres. We propose that these increased abundances may be the result of warmer temperatures during the dust storm causing stronger atmospheric circulation and preventing ice cloud formation, which may confine water vapour to lower altitudes through gravitational fall and subsequent sublimation of ice crystals. The observed changes in H2O and HDO abundance occurred within a few days during the development of the dust storm, suggesting a fast impact of dust storms on the Martian atmosphere

No detection of methane on Mars from early ExoMars Trace Gas Orbiter observations

The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere, which-given methane's lifetime of several centuries-predicts an even, well mixed distribution of methane. Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections. We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally

Estimate of aeolian dust thickness in Arabia Terra, Mars: implications of a thick mantle (> 20 m) for hydrogen detection

This study describes a method for estimating dust thickness on the surface of Mars using the distribution of small impact craters (3 Ga). Results also suggest that hydrogen, detected by the Neutron Spectrometer within this region in the top meter, is present in the dust and not in the underlying bedrock.Notre étude présente une méthode d’estimation de l’épaisseur de poussière à la surface de Mars en utilisant les petits cratères d’impact (< 1 km de diamètre) observés à haute résolution avec l’imagerie de l’instrument Mars Observer Camera de la sonde Mars Global Surveyor. La distribution des petits cratères est différente de celle prédite par le flux météoritique car les cratères sont progressivement recouverts de dépôts éoliens. La hauteur des remparts des plus gros cratères non enfouis permet d’obtenir une estimation approximative de l’épaisseur de ces dépôts éoliens. Cette méthode est appliquée à la région d’Arabia Terra. Les résultats montrent une couverture de poussière d’environ 20 m au minimum. Ceci indique que cette région est une zone de dépôt durant la période Amazonienne (< 3 Ga). Notre étude suggère également que l’hydrogène, qui est détecté par le spectromètre Neutron de Mars Odyssey dans cette région, se localise dans les dépôts éoliens et non pas dans le socle sous-jacent

Observational evidence for a dry dust-wind origin of Mars seasonal dark flows

Seasonal flows on warm slopes, or recurring slope lineae ("RSL"), have been presented as strong evidence for currently flowing water on Mars. This assumption was supported by a correlation between activity and warm temperatures, and by the spectral identification of hydrated salts. Here we first demonstrate that salts spectral identification is not robust, and that flow activity occurs on a wider range of seasons and slope orientations than previously thought, ruling out liquid water as a probable contributor. We then show that morphology, location and timing of flow activity is fully consistent with the removal and deposition of bright dust above darker underlying surfaces occurring notably in relation with seasonal dust storm activity. Mars recurring slope lineae are thus consistent with dust movements typical of present-day dry planet Mars

MicrOmega/MASCOT first results

International audienceMASCOT has been selected to be integrated on board the JAXA Hayabusa2 mission, with a suite of 4 instruments: a camera MASCam, a radiometer MARA, a magnetometer MASMag and MicrOmega, a hyperspectral near infrared microscope, designed to characterize the composition of Ryugu surface materials down their grain scale (25 μm large). A joined article (Ho et al., this issue) describes and gives references to MASCOT design, goals, development and operation, along its cruise, landing and on asteroid phase. MicrOmega has been activated and operated as planned, while demonstrating high instrumental performances. However, its configuration when MASCOT went at rest on Ruygu located MicrOmega line of sight over a deep depression, with Ryugu surface much too far to be illuminated and imaged, precluding a direct characterization. In this paper, we present and discuss MicrOmega operations and outcomes