Quantitative comparison of morphometric and hydrological characteristics of valley networks between Evros Vallis on Mars and Kaidu River in Tarim Basin as terrestrial analog

Abstract

The evolution process of the generation, development, and extinction of valley networks on Mars and its analog on Earth should be understood by conducting a comparative study from the viewpoint of comparative planetology, which may be ultimately meaningful for exploring the ancient life relics on Mars. The valley networks of Evros Vallis on Mars and Kaidu River in the Tarim Basin in Xinjiang are extracted from the Mars Orbiter Laser Altimeter (MOLA) and ASTER Global Digital Elevation Map (ASTER GDEM) data. Then, the morphometric and hydrological parameters, namely, the mean length of tributaries at all levels, mean sinuosity at all levels, drainage density, channel density, river gradient, and stream fractal dimension of the entire valley networks, are calculated and compared. Both valley networks are quasi-dendritic valley systems, and the quantitative calculation results show the following. (1) The mean length of tributaries at all levels of Evros Vallis is 1.4 to 2.5 times longer than that of Kaidu River, which indicates that the scale of Evros Vallis is generally larger. (2) The average of the mean sinuosity of tributaries at all levels of Evros Vallis is 1.19, which indicates straightness; that of Kaidu River is sinuous and larger, with an average value of 1.35. (3) The stream fractal dimensions of Evros Vallis and Kaidu River are 1.63 and 1.70, respectively, which demonstrates that the geomorphic development stage of both drainage basins is at the end of topographic infancy and the beginning of maturity. However, the drainage and channel densities of the former are much smaller than those of the latter, indicating that the overall development stage of the former is less than that of the latter. (4) The longitudinal profile of Evros Vallis shows a concave-down trend with a relative gentle channel. Its river gradient is 1.63‰, and the river gradient of Kaidu River is 3.74‰. Its longitudinal profile can be divided into two as follows: the source section is concave-down, with a gentle channel and river gradient of 2.54‰, and the estuary section is concave-up, with a steep channel and river gradient of 5.18‰. The morphometric and hydrologic parameters of Evros Vallis on Mars are similar to those of natural rivers on Earth. In addition, fluvial landforms are found in the main stream channel, desiccation mud crack polygons, and rampart craters of Evros Vallis, showing that water and/or ice once existed when Evros Vallis was dry, as observed on the downstream channel. These features strongly suggest that this drainage area was formed by a long time of runoff erosion. However, the water source and duration still require further studies by combining the research outcomes in regional and global paleogeography and paleoclimate.