Mathematics – Logic
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....5917r&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #5917
Mathematics
Logic
Scientific paper
The appearance of the impact craters on the Martian surface depends on numerous factors beginning from the size, mass, velocity, type, and impact angle of the approaching projectile [1]. These all have affected on the impact energy delivered into the surface. The bedrock properties have then resulted in additional effects. Besides some major phenomena (Pre-existing faults and fractures, permafrost-saturated layers) there may have been numerous more delicate variations due to local projectile-bedrock combinations. Various post-impact deformation processes may then have changed the appearance of an impact crater to the extent that it is difficult to identify any original crater characteristics in great details. The changes in the crater appearances can, however, be looked in a positive way to provide crucial information on the local surface geology, bedrock properties and, more generally, on the whole post-impact geological evolution of the area studied [2,3,4]. We have characterized and studied the various crater deformation types found from within the large Hellas area. As it is one of the possible previous water body areas on Mars and lies also close to the southern permafrost and the south-pole environment, many craters locating within the greater Hellas Basin area have undergone substantial fluvial processes. Still, many of their surviving geologic features are enough well preserved. The good state of preservation is due partly to the relative youth of the craters and/or partly to Martian relative dryness. The absence of permanent water cover limits the weathering of surface materials, while it optimizes the site's exposure for geologic surveys by remote-sensing. This allows to estimate that the effects related to permafrost, water, erosion and sedimentation have been far more important within the greater Hellas area than what was earlier assumed using the previous data sets which have had defects either in resolution or in areal coverage. The still-cumulating MOC and THEMIS-VIS data are steps to the right direction but the more complete realization of the effect of fluvial processes will still wait for more complete coverage possibly acquired by the MEX HRSC camera. References: [1] Melosh, H.J. (1989) Impact Cratering. A Geologic Process, Oxford Univ.Press, 245 pp. [2] Öhman, T. et al. (2003) LPSC 34, pdf #1311. [3] Stewart et al. (2001) LPSC 32, pdf #2092. [4] Ormö J. and P. Muinonen (2000) LPSC 31, pdf #1266.
Aittola Marko
Kostama Veli-Petri
Lahtela H.
Raitala Jouko
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