We performed high-resolution computer simulations of impacts into homogeneous and layered martian terrain analogs to try to account for the ages and characteristics of the martian meteorite collection found on Earth. We found that craters as small as approximately 3 kilometers can eject approximately 10(7) decimeter-sized fragments from Mars, which is enough to expect those fragments to appear in the terrestrial collection. This minimum crater diameter is at least four times smaller than previous estimates and depends on the physical composition of the target material. Terrain covered by a weak layer such as an impact-generated regolith requires larger, therefore rarer, impacts to eject meteorites. Because older terrain is more likely to be mantled with such material, we estimate that the martian meteorites will be biased toward younger ages, which is consistent with the meteorite collection.

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We present a navigation technique for a lunar vehicle based upon matching horizon imagery with a database of synthetic panoramas generated from ultrahigh-resolution topographic models created by stereophotoclinometry. We conducted two tests, one with lunar topography and fully synthetic panoramas, and another using Earth-based data and actual panoramic images. We have shown that the horizon-matching technique can search a wide area for a vehicle's location and determine that location to within 6 m using readily available imagery.

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