Atmospheric Entry Studies and the Smallest Impact Craters on Mars

J. Cintala, W. C. Rochelle, C. M. Mitchell, R. N. Smith, J. Dobarco-Otero, B. K. Finch, and T. H. See; Astromaterials Research Office, NASA Johnson Space Center, Houston, Texas 77058, Lockheed-Martin Space Operations, 2400 NASA Parkway, Houston, Texas 77058. Introduction: High-resolution images from the Mars Orbiter Camera reveal impact craters as small as 10 m [1], and still smaller craters ( 0.95 ru ; ru thus defines the smallest impactor size that is minimally ablated after complete passage through the atmosphere. It follows that all objects > ru will reach the martian surface without significant mass loss. Note, however, that the impact velocity (Vu) of these relatively large objects may be significantly affected, especially at γ < 30°. Nevertheless, many chondrites some 10 cm across will reach Mars at some 80 to 90% of their initial impact speed and all meter-sized objects will be minimally decelerated. Although not listed, the effective impact angle at the martian surface is generally steeper than the initial entry angle, yet rare exceptions exist.