Martian geomorphology from fractal analysis of drainage networks

An alternative approach to conventional planetary terrain analysis is proposed. Martian terrains, represented by topography based on the Mars Orbiter Laser Altimetry (MOLA) data, are represented as a series of drainage basins, regardless of the historical presence or absence of actual fluid flow. A fractal analysis of each drainage network, computationally extracted from an underlying terrain, yields a network descriptor, a list of four numbers that describes the traits of a network. Network descriptors are used for a quantitative characterization and classification of Martian surfaces. We have extracted and analyzed 387 drainage networks from 74 Martian locations, representing all major epochs and geological units, to investigate whether their network descriptors are capable of differentiation between different epochs and geological units. We have found that our approach can distinguish morphologically different terrains, but only in a statistical sense. In particular, the method could be used to measure the degree of surface cratering and thus the age of the surface. In addition, for surfaces that are not heavily cratered the method is capable of distinguishing between different geological units. We have found no global trends in the character of Martian drainage networks; their network descriptors show no systematic dependence on location or elevation. Our analysis reveals that all Noachian surfaces grouped in the Npld geological unit have very similar network descriptors, regardless of prominence and integration of their visible fluvial features. The comparison between statistical description of Npld and terrestrial drainage networks shows overall similarities, but also some marked differences. Because of these differences, the notion of sustained rainfall on Mars during the Noachian epoch is inconsistent with our findings, but a limited rainfall is compatible with our results.