QUANTITATIVE COMPARISON OF SHOEMAKER FORMATION EJECTA WITH RIES CRATER BRECCIA AND SUEVITE

The rover Opportunity has examined rocks that lie on the rim of the Endeavour impact crater on Mars. These basaltic impact breccias were imaged by Opportunity using its 360 degree panoramic cameras. It is proposed that these rocks are examples of the suevite found at Ries Crater in Germany. Suevite is a breccia characterized by angular clasts of rocks and minerals as well as impact glasses, set in a fine-grained matrix. The objective of this study is to understand the processes under which Endeavour crater formed. The area, perimeter, and circularity of the clasts within the Endeavour ejecta were measured and compared to previously published clast measurements from Ries suevite. Preliminary results show the Endeavour clasts are more evenly distributed over all size ranges, whereas the majority of clasts from Ries suevites lie within a narrow range of sizes. The size “sorting” displayed in the Ries suevites and the even distribution of clasts from Endeavour crater may indicate that the Endeavour rocks were part of the ballistic impact deposits in contrast to the fallout suevite.