Modes of ejecta emplacement at Martian craters from laboratory experiments of an expanding vortex ring interacting with a particle layer

International audience[1] Ejecta morphologies of many Martian craters indicate fluidized emplacement which differs from ballistic emplacement in dry, airless environments. Double Layered Ejecta craters possess particularly interesting ejecta morphologies: two lobes and radial lineations on their surface, which probably result from gas-dominated radial flow during the emplacement. To examine how a radial flow interacts with surface particles to generate some of the observed morphologies on Mars, we have conducted water tank experiments in which a vortex ring encounters a particle layer. The threshold of particle motion and three interaction modes are described by two dimensionless numbers: particle Shields' parameter and particle Reynolds number. Our results show that gas-dominated flows are possible during cratering and could be used to constrain the ancient Martian environment from observations. Citation: Suzuki, A., I. Kumagai, Y. Nagata, K. Kurita, and O. S. Barnouin-Jha (2007), Modes of ejecta emplacement at Martian craters from laboratory experiments of an expanding vortex ring interacting with a particle layer, Geophys