HR: 0800h
AN: P41A-0224    [Abstracts]
TI: Planetary Scale Impacts and Consequences for the Mars Hemispheric Dichotomy
AU: * Marinova, M M
EM: mmm@caltech.edu
AF: Dept. of Geological and Planetary Sciences, California Institute of Technology, MC 150-21, Pasadena, CA 91125, United States
AU: Aharonson, O
EM: oa@gps.caltech.edu
AF: Dept. of Geological and Planetary Sciences, California Institute of Technology, MC 150-21, Pasadena, CA 91125, United States
AU: Asphaug, E
EM: asphaug@mac.com
AF: Earth and Planetary Sciences Dept., University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064, United States
AB: Planetary-scale impacts are events in which the resultant impact basin is a significant fraction of the planet's circumference. The curvature of the planet is expected to be important in the impact process, especially as it relates to the fate of downrange ejecta in off-axis events. Planetary-scale impacts are abundant in the Solar System, especially early in its evolution. A possible candidate planetary-scale impact basin is the Martian hemispheric dichotomy, expressed as a difference in surface elevation, crustal thickness, and surface age between the northern lowlands and the southern highlands. We investigate the characteristics of planetary-scale impacts, and in particular the effects of a mega impact on Mars. We use a 3 dimensional self-gravitational Smoothed Particle Hydrodynamics (SPH) model to simulate the impacts, implementing an olivine equation of state derived for the Tillotson formulation, and use this to establish the initial pressure and internal energy profile of the planet. The parameter space of impactor energy, impactor size, and impact velocity are explored for Mars hemispheric impacts. We find that for a given impact energy, head-on large but slow impacts produce more melt and cover more of the planet with melt than small, fast, and oblique events. Head-on impacts produce crustal blow-off and a melt pool at the antipode. Oblique impacts do not cover much of the planet with melt, but create sizable basins. Various degrees of crustal thickening are apparent around the crater over a length of ~1000 km; this crustal thickening could relax over geological time. Fast impacts eject material with escape velocity many times their own mass. In all cases, less than 10% of the impactor's mass is placed in orbit. For oblique events, a significant fraction of the angular momentum in the system is carried away by escaping material, limiting the efficiency of angular momentum transfer to the planet.
DE: 5420 Impact phenomena, cratering (6022, 8136)
DE: 5455 Origin and evolution
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting