Mathematics – Logic
Scientific paper
Jul 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000came.work...19b&link_type=abstract
Concepts and Approaches for Mars Exploration, p. 19
Mathematics
Logic
Atmospheric Models, Mars Atmosphere, Thermosphere, Accelerometers, Instrument Packages, Boundary Conditions, Atmospheric Temperature, Density (Mass/Volume), Three Dimensional Models, Atmospheric Circulation
Scientific paper
Besides its variations related to solar cycle and seasonal effects, the Martian thermosphere also displays specific responses to propagating gravity waves, dust storm heating and interaction with the solar wind. All these effects, which strongly affect the density and temperature structure of the upper atmosphere as well as the wind pattern, are of significant importance for the understanding of the dynamics and of the short and long term evolution of the global planetary environment. As a matter of fact, ongoing studies have shown that the lower and middle atmosphere are rather sensitive to conditions in the thermosphere; consequently, numerical simulations of the Martian meteorology through General Circulation Models require that the boundary conditions be known with a good accuracy at thermospheric altitudes as high as 150 km and even higher. In this altitude range, the coupling with the solar wind and its consequences on energy input both depend upon and influence the large scale structure of the upper atmosphere. The long term evolution and erosion of the atmosphere by the solar wind definitely appear as a key question to be investigated by the future Martian program. A detailed and quantitative understanding of the various mechanisms which can presently play a role is needed to estimate their effectiveness back over the geological times and describe their possible effects on the climatic variations. This can only be achieved through a precise knowledge of the structure thermosphere and of its temporal variations. Last but not least, insertion in Mars orbit of future scientific or telecommunication satellites will certainly rely on aerocapture and aerobraking which, compared to the classical chemical technique, allow for a very large mass saving. Reliable and safe orbit insertion and orbital operations require that accurate models of the structure of the atmosphere and its predicted variations be available. The response of the Martian environment above about 100 km to the various processes mentioned above are at present very poorly constrained by available measurements. Upcoming missions to Mars such as Planet-B and Mars Express will not provide in situ measurements down to the lower thermosphere of Mars, in the altitude range between 100 and 150 km where considerable variability has been observed recently by the Mars Global Surveyor (MGS) Accelerometer during aerobraking campaigns. The Mars Thermospheric General Circulation Model (MTGCM) is a 3-D modeling tool that is presently being used to simulate the Mars upper atmosphere structure and dynamics in the altitude range from about 70 to 300 km. The simulation runs for various solar fluxes, seasons, and dust heating conditions were only crudely constrained by Mariner, Viking, Pathfinder, and MGS observations since the available in-situ data span only a fraction of the solar cycle and Mars seasons. A long-term program to monitor the structure of the Martian thermosphere from about 100 km up to about 250 km is thus proposed which can take benefit of multiple opportunities to provide the necessary coverage of the various conditions which affect the global environment of Mars. The ultimate goal is to build a data base for the climatology of the lower thermosphere of Mars which can be used to constrain the models.
Berthelier Jean-Jacques
Bougher Stephen
Chassefiere Eric
Duvet Ludovic
Forget Francois
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