Statistics – Applications
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....12131b&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #12131
Statistics
Applications
Scientific paper
Aerosol dust suspended in the atmosphere thermally influences the behaviour of the lower atmosphere by absorbing solar radiation and by increasing the thermal inertia. Main dust parameters influencing the atmosphere heating are size distribution, albedo, single scattering phase function, imaginary part of the index of refraction. Moreover, atmospheric dust seems to have had long term effects on the surface geology, too. In fact, in the present environment of Mars, the most active surface modifying agent is the wind. Vast dune fields, various albedo patterns that change with time, wind eroded hills and drifts of fine grained material observed at the Viking landing sites are all attributed to aeolian processes. Large parts of the cratered uplands and smooth terrain in both polar regions are believed to be composed of deposits of windblown particles. These deposits may be important reservoirs for volatiles and may influence climate changes via variation of regional albedo. It is clear that the knowledge of the atmospheric dust properties and the mechanisms of dust settling and raising into the atmosphere are important to understand the climate and the surface evolution on Mars. Dust deposition also may be a key process in the volatile cycle on the planet. In situ results obtained so far do not give exhaustive information on dust physical properties and concentration near the surface. On the other hand H_2O is important as indicator of global climate changes on long time-scales and has fundamental links to life forms origin. Furthermore, the past volcanism on Mars, associated with a "wetter" environment, most probably caused in the past hydro-thermal activities that would be particularly suited for the existence of the most primitive organisms. Most of our understanding of the water vapour circulation derives from orbiter-based observations by the Mars Atmospheric Water Detection experiment, onboard the Viking Orbiters and from the Thermal Emission Spectrometer (TES) onboard the Mars Global Surveyor. Seasonal variations in the column abundance are due to the combined effect of exchange of H_2O between atmosphere and water reservoirs (i.e. polar caps, regolith) and atmospheric transport. Despite the low absolute water content (0.03% by volume), relative humidity can exceed 100% leading to frosting phenomena, thanks to low Martian temperatures. The typical value of the pressure at surface, close to the triple point value of water phase diagram, makes the persistence of liquid water at the surface of Mars highly improbable. This means that the water is probably present exclusively in gaseous and solid states, at the surface level. Attempts to use space-born and earth-based observations to estimate quantitatively surface and near-surface sources and sinks of water vapour have had good but also partial success. Most important questions that appear from the present knowledge is how the water vapour atmospheric circulation occurs and how to explain the difference in the hemispheric and seasonal behaviour of the water vapour. Despite TES results showed that a percentage of hemispheric "asymmetry" of the seasonal vapour abundance was probably due to the presence of two dust storms during MAWD observations, an evident difference remains partially unexplained. In this context, it is extremely important to study the role of the different contributions to the production of atmospheric vapour from the main reservoirs and to the formation of water ice clouds most probably catalysed by the atmospheric dust. At present, no in situ measurement of water vapour content was performed yet. We discuss the possibility of using a new concept instrument for extraterrestrial planetary environments, based on the past experience acquired for dust monitoring in space and on Earth and new possible technologies for space applications. MEDUSA (Martian Environmental Dust Analyser) project is a multisensor and multistage instrument based on an optical detector of dust grains, coupled with an impact sensor and a cascade of collecting sensors (microbalances). It that will provide a complete set of measurement about the grain size and mass distribution, number density in atmosphere and scattering properties. MEDUSA instrument can measure for the first time, directly and quantitatively, the physical and dynamical properties of atmospheric dust and the water vapour concentration on Mars.
Battaglia R.
Colangeli Luigi
Della Corte V.
Esposito Floriana
Ferrini Giulia
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