Whether bright frosts also occur in the south polar region is unknown. Photogeologic units were identified based on albedo, crater density, surface features, and cross-cutting relations. All craters larger than 60 km in diameter were mapped and classified according to their stage of degradation. Because the poor resolution makes crater counting difficult and correlation of counts between areas uncertain, qualitative estimates of crater frequency rather than quantitative counts were used to gain insight into relative unit ages. The surfaces seen thus far on Callisto seem to be remarkably simple for such a large satellite.
Line geometry is topologically clean.
Photogeologic units were identified based on albedo, crater density, surface features, and cross-cutting relations. All craters larger than 60 km in diameter were mapped and classified according to their stage of degradation. Because the poor resolution makes crater counting difficult and correlation of counts between areas uncertain, qualitative estimates of crater frequency rather than quantitative counts were used to gain insight into relative unit ages. The surfaces seen thus far on Callisto seem to be remarkably simple for such a large satellite. Information has been obtained from sources believed to be reliable, but its accuracy and completeness and the opinions based thereon, are not guaranteed.