AN ATMOSPHERIC BLAST/THERMAL MODEL FOR THE FORMATION OF HIGH-LATITUDE PEDESTAL CRATERS

Abstract

Although tenuous, the atmosphere of Mars affects the evolution of impact-generated vapor. Early-time vapor from a vertical impact expands symmetrically, directly transferring a small percentage of the initial kinetic energy of impact to the atmosphere. This energy, in turn, induces a hemispherical shock wave that propagates outward as an intense airblast (due to high-speed expansion of vapor) followed by a thermal pulse of extreme atmospheric temperatures (from thermal energy of expansion). This study models the atmospheric response to such early-time energy coupling using the CTH hydrocode written at Sandia National Laboratories. Results show that the surface surrounding a 10 km diameter crater (6 km "apparent" diameter) on Mars will be subjected to intense winds (~200 m/s) and extreme atmospheric temperatures. These elevated temperatures are sufficient to melt subsurface volatiles at a depth of several centimeters for an ice-rich substrate. Ensuing surface signatures extend to distal locations (~4 apparent crater diameters for a case of 0.1 % energy coupling) and include striations, thermally armored surfaces, and/or ejecta pedestals - all of which are exhibited surrounding the freshest high-latitude craters on Mars. The combined effects of the atmospheric blast and thermal pulse, resulting in the generation of a crater-centered erosion-resistant armored surface, thus provide a new, very plausible formation model for high-latitude Martian pedestal craters. © The Meteoritical Society, 2006.