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.%从比较行星学的角度,开展火星典型河网和地球类比区河网对比研究,对深入理解火星表面河网产生、发展和消亡的时空演变过程,甚至对探索火星古老生命遗迹均具有重要意义.分别基于MOLA和ASTERGDEM高程数据,提取了火星Evros Vallis和新疆塔里木盆地开都河流域的河网水系,定量计算并比较了各级河流平均长度、各级河流平均弯曲系数、河网密度、河道密度、河道比降、河网分维数等河网形态与水文特征参数.结果显示:(1)Evros Vallis流域各级河流平均长度是开都河流域长度的1.4--2.5倍,说明Evros Vallis流域河流的规模普遍较大;(2)Evros Vallis流域各级河流平均弯曲系数为1.19,为平直河流;开都河流域各级河流平均弯曲系数均值为1.35,为弯曲河流;(3)Evros Vallis和开都河流域的河网分维数分别是1.63和1.70,表明这两个流域的地貌发育均处于幼年期刚刚结束,壮年期才开始的阶段,但前者的河网密度和河道密度均远小于后者,说明其整体发育程度小于后者;(4)Evros Vallis干流纵剖面整体呈现下凹趋势,河道相对平缓,比降为1.63‰;整个开都河干流的河道比降为3.74‰,其纵剖面整体形态可划分为两部分,河源这一段为下凹型,河道较平缓,比降为2.54‰,河口这一段为上凸型,河道较陡峭,比降为5.18‰.Evros Vallis的流域形态与水文参数与地球上自然形成的流域的形态与水文特征参数非常相似,并且其干流河道内还能观察到心滩等典型河流地貌、河流干涸过程中形成的泥裂以及表明水/冰曾存在的壁垒撞击坑,这些特征强烈显示该流域是长期水流冲刷侵蚀形成.
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