The distribution of bright and dark material on Ganymede in relationship to surface elevation and slopes

The unique high-resolution digital terrain data set available for Ganymede' s Uruk Sulcus area and Galileo Regio is analyzed by quantitative image anal ysis techniques to identify relationships between surface brightness, eleva tion, and slopes. Broad and narrow ridges and grooves of the Uruk Sulcus te rrain model are found to be aligned with bright and dark lineament patterns visible in images. These prominent lineaments represent areas covered by b right and dark albedo material, not effects of photometric shading. There i s a strong correlation between material locations and elevation: bright mat erial is found on topographic highs, whereas dark material is located in de pressions; the relative abundance of the dark material increases with lower elevation. In Galileo Regio, we find that bright material is also located on slopes facing north. We suggest that the bright material in Uruk Sulcus and Galileo Regio was emplaced or exposed during or after formation of the terrain in its present location, whereas the dark material was eroded and r edistributed down-slope. Effects of net solar illumination may play a role in the peculiar azimuthal distribution of bright and dark material on slope s. (C) 1999 Academic Press.