Subsurface Investigations by MARSIS in Mars Express Mission

The MARSIS primary scientific objectives are to map the distribution of water, both liquid and solid, in the upper portions of the crust of Mars. Detection of such reservoirs of water will address key issues in the hydrologic, geologic, climatic and possible biologic evolution of Mars, including the current and past global inventory of water, mechanisms of transport and storage of water. Three secondary objectives are defined for the MARSIS experiment: subsurface geologic probing, surface characterization, and ionosphere sounding. According to the previous scientific objectives, this paper provides a description of the design approach, expected performances and first science results of the MARSIS. In order to assess the performances, taking into account of Mars Orbital Laser Altimeter (MOLA) data, some models, either dielectric and geometric, of the Martian crust have been worked out, being the related structure the result of many different processes and validate by the preliminary results. Moreover the two most likely scenarios representing the relevant interfaces MARSIS are: Ice/water(I/W) interface - in this scenario the pores are filled with ice from the surface down to a depth below which liquid water is stable and becomes the pore-filling material. Dry/ice(D/I) interface - here the pore-filling material is considered to be gas or some other vacuum-equivalent material up to a depth, below which ice fills the pores. Hence the interface to detect is between dry regolith and ice-filled regolith.