Properties of Martian Highlands Drainage from Themis Images and Mola Topography

Valley networks are mapped from mosaics composed of 100 m/pixel THEMIS images for 8 sites in Martian highlands. The sites are subdivided into individual drainage basins using 500 m/pixel DEMs co-registered with image mosaics. Terrain parameters are calculated for each basin with area > 10 km. Drainage densities of individual basins are 0 0.29 km−1. There is a moderate (r=0.5) correlation between values of drainage density and relief, no other terrain parameters are correlated. Within a given site, the basins show evidence of past integration disrupted by subsequent cratering. Morphologically, the basins are divided into 5 classes. There is no clear correlation between basin’s morphologic class and the value of any of the terrain parameters. In particular, heavily dissected and undissected basins are found in all morphological classes. Introduction. We map valley networks in eight large (∼ 10 km) Noachian sites using mosaics of 100m/pixel THEMIS daytime images. The results are compared to previous mapping [1] based on 256m/pixel global mosaic constructed from MOC images. They are also compared to results of automatic mapping [2] based on 500m/pixel digital elevation models (DEMs) constructed from topography data collected by MOLA instrument. The DEMs are also used to divide each site into constituent drainage basins. Overall, 83 non-crater basins having areas > 10 km are extracted from all eight sites. For each basin we calculate several terrain parameters including a drainage density. Drainage density is calculated using our new manual mapping of valley networks. We study the issue of integration of drainage basins by subdividing the sites into progressively smaller basins. Finally, we compare quantitatively morphologies of drainage basins using the circularity function method [3]. The 83 basins are classified into five morphologic classes on the basis of similarity between their circularity functions. We study correlations between pairs of basin’s terrain parameters, as well as between basin’s morphologic class and the values of terrain parameters. The overall purpose of this study is to understand a fluvial environment responsible for formation of valley networks during the Noachian era in Martian history. Mapping. The ISIS software was used to construct the mosaics of each site using 15-40 THEMIS images (band 1) covering a given site. The sites are: Locras Valles (6.0, 11.0, 45.0, 49.0), Pollack (-11.1, -6.7, 27.8, 34.8), Evros Vallis West (-15.8, -10.2, 10.8, 18.0), Evros Vallis North (-11.3, -5.3, 11.6, 18.6 ), Dawes East (-8.4, -3.2, 42.5, 47.9), Millochou West (-23.4, -16.9, 84.7, 91.7), Millochou South (-26.0, -20.0, 85.0, 91.0), and Naktong Vallis (1.0, 9.0, 28.0, 36.0). The number in brackets indicate site’s location: latitude of the lower edge, latitude of the upper edge, east longitude of the left edge, and east longitude of the right edge, respectively. The valleys were mapped manually by drawing over an image in the ArB A