Planetary surfaces are made of solid matter and are affected by endogenic and exogenic processes. These processes affect the morphology and composition of the surface. Therefore, the investigation of planetary surfaces can teach us about the origin and evolution of planetary bodies. The structure of a surface can be inferred from its morphology, which allows the spatial interpretation of surface features and, with additional topographic information, of their quantitative three-dimensional characteristics like slopes, depths, volumes etc. From morphological and topographical information, the quantity of eroded material can be estimated, which is important for understanding surface-forming processes. Surface features can be grouped into geological units and mapped, based on their size, shape, texture, and albedo. Surface materials may differ in composition, associated with distinct spectral characteristics. The mineral and chemical content of geological units can be determined by analyzing their spectral reflectance.
In our Solar System planetary bodies collide with each other very often. All solid surfaces exhibit traces of these catastrophes in the form of impact craters. We can estimate the age of a surface unit by measuring the size and distribution of its craters. Data about structures, spatial distributions, compositions, and ages are used to define and map geological units. By classifying these individual units in time and space, it is possible to determine the so-called stratigraphic sequence of geologic events.
Additional to classifications like this, comparative studies are important for interpreting surface processes on planetary bodies. This is used also for understanding early processes on Earth, where almost all geologic evidences and indicates are lost due to dynamic plate tectonic processes. One of the main questions in this context concerns the habitability of planetary surfaces and their potential for generating life.
For further information see also:
Planetary Image Facility(RPIF) desktopdefault.aspx/tabid-723/1196_read-2164/Planetary Data System http://pds.jpl.nasa.gov/Planetary Science Archive http://www.rssd.esa.int/index.php?project=PSAPhotojournal http://photojournal.jpl.nasa.gov/