Snow carrots after the Chelyabinsk event and model implications for highly porous solar system objects
Luther, R., Artemieva, N., Ivanova, M., Lorenz, C. and Wünnemann, K.
Meteoritics & Planetary Science. doi: 10.1111/maps.12831
“After the catastrophic disruption of the Chelyabinsk meteoroid, small fragments formed funnels in the snow layer covering the ground. We constrain the pre-impact characteristics of the fragments by simulating their atmospheric descent with the atmospheric entry model. Fragments resulting from catastrophic breakup may lose about 90% of their initial mass due to ablation and reach the snow vertically with a free-fall velocity in the range of 30–90 m s−1. The fall time of the fragments is much longer than their cooling time, and, as a consequence, fragments have the same temperature as the lower atmosphere, i.e., of about −20 °C. Then, we use the shock physics code iSALE to model the penetration of fragments into fluffy snow, the formation of a funnel and a zone of denser snow lining its walls. We examine the influence of several material parameters of snow and present our best-fit model by comparing funnel depth and funnel wall characteristics with observations. In addition, we suggest a viscous flow approximation to estimate funnel depth dependence on the meteorite mass. We discuss temperature gradient metamorphism as a possible mechanism which allows to fill the funnels with denser snow and to form the observed “snow carrots.” This natural experiment also helps us to calibrate the iSALE code for simulating impacts into highly porous matter in the solar system including tracks in the aerogel catchers of the Stardust mission and possible impact craters on the 67P/Churyumov-Gerasimenko comet observed recently by the Rosetta mission.”