FORMATION OF AIRBLAST FEATURES ASSOCIATED WITH YOUNG MARTIAN CRATERS

New small craters on Mars are sometimes surrounded by a roughly circular dark area that is different from and generally larger than its ejecta blanket and any associated rays. This circular area is interpreted as an "airblast", wherein the shockwave propagating through the atmosphere blows away or otherwise disturbs a layer of dust surrounding the new crater (or craters, in the event of an atmospheric breakup of the projectile.) In this work we perform systematic measurements of a number of these airblast craters to ascertain what controls the diameters of the airblasts. Previous work has indicated that the normalized airblast diameter is not correlated with crater diameter. We examined each of the 249 new martian craters for which there are before and after impact images, meaning these craters are all less than about 10 years old. We studied in detail 25 of those craters that had clear airblast features. For each crater, we processed the raw HiRISE data in ISIS and used ISIS qview to measure both the crater diameters and the airblast diameters. For each crater we divide the airblast diameter by the crater diameter to determine the normalized airblast diameter, which gives how many times bigger the airblast is than the crater. For the craters we studied, the normalized airblast diameters range from 20-95. We assume the airblast is created by a shock wave propagating through the atmosphere away from the crater and disturbing the top layer of dust. For each airblast crater we determine local surface roughness, thermal inertia, dust cover index, and terrain type. We also compare these properties for craters with and without airblast features. This work provides insight into the factors that control the formation of these common airblast features.