Impact cratering of granular mixture targets made of H2O ice-CO2 ice-pyrophylite

Experiments related to impacts onto three-component targets which could sim ulate cometary nucleus or planetary regolith cemented by ices are presented here. The impact velocities are from 133 to 632 m s(-1). The components ar e powdered mineral (pyrophylite), H2O ice, and CO2 ice mixed 1 : 1 : 0.74 b y mass. The porosity of fresh samples is about 0.48. Two types of the sampl es were studied: nonheated samples and samples heated by thermal radiation. Within the samples a layered structure was formed. The cratering pattern s trongly depended on the history of the samples. The craters formed in nonhe ated targets had regular shapes. The volume was easy to be determined and i t was proportional to impact energy E. The crater depth scales as E-0.5. Im pacts on the thermally stratified target led to ejection of a large amount of material from the loose sub-crustal layer. For some particular interval of impact velocity a cratering pattern can demonstrate unusual properties: small hole through the rigid crust and considerable mass transfer (radially , outward of the impact point) within sub-crustal layer. (C) 2000 Elsevier Science Ltd. All rights reserved.