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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Kilometer-scale slopes on Mars and their correlation with geologic units: Initial results from Mars Orbiter Laser Altimeter (MOLA) data
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Kilometer-scale slopes on Mars and their correlation with geologic units: Initial results from Mars Orbiter Laser Altimeter (MOLA) data

机译：火星上的千米比例坡度及其与地质单位的关系：来自火星轨道激光高度计（MOLA）数据的初步结果

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摘要

Martian surface slopes were calculated at baselines from 0.4 to 25 km using profiles obtained by the Mars Orbiter Laser Altimeter (MOLA) instrument during the aerobraking phase of the Mars Global Surveyor mission, Median slope is proposed as a characteristic measurement of the typical surface roughness at each corresponding scale. Median slope is favored over RMS slope because it is not influenced by the small number of higher slopes at the upper end of the slope-frequency distribution tail. Median slope complements interquartile scale roughness characterization in that it is more sensitive to smaller baseline slopes. A map of the median slope of the northern hemisphere is presented. Median slopes and their scale dependences are used to characterize typical kilometer-scale roughness for a set of geologic units mapped in the northern hemisphere. This analysis demonstrates that many individual units and groups of units are characterized by distinctive surface slopes and that these characteristics are sufficiently different that they hold promise for use in the definition and characterization of units. Characterization of the slope properties of geologic units provides information useful in the interpretation of their origin and evolution. For example, the generally smooth topography of the diverse Vastitas Borealis Formation subunits is dominated by about 3 km, 0.3 deg steep features almost indistinguishable in Viking images. The roughness characteristics of this unit differ from those of other geologic units on Mars and suggest some distinctive process(es) of formation and/or modification of kilometer-scale topography common for all subunits. The similarity of roughness characteristics of the several highland plateau units suggests that kilometer-scale topography was largely inherited from the period of heavy bombardment. The northern polar cap and layered terrains are largely very smooth at small scale. The long, steep-sloped tails of the slope-frequency distributions are compared for the dominant terrain types in the northern hemisphere of Mars and are compared with Earth continents. The Vastitas Borealis Formation found in the northern lowlands differs significantly from both cratered uplands and volcanic plains, and these latter two units can be distinguished from each other on the basis of median slope. Terrestrial continents are smoother than cratered highlands but rougher than the Vastitas Borealis Formation and most volcanic plains. An inventory of all observed slopes much steeper than the angle of repose is presented. Steep slopes occur in the upper parts of tectonic scarps, most likely representing bedrock exposures. The presence of extremely steep slopes in the presumably ductile polar cap provides evidence for geologically recent and/or ongoing formation of these slopes.
机译：火星表面坡度是在火星全球测量师飞行任务的航空制动阶段使用火星轨道激光高度计（MOLA）仪器在0.4至25 km的基线处计算得出的，建议采用中位坡度作为典型表面粗糙度的特征测量。每个相应的比例。中间斜率优于RMS斜率，因为它不受斜率频率分布尾部上端的少量较高斜率的影响。中位斜率补充了四分位尺度的粗糙度特征，因为它对较小的基线斜率更敏感。给出了北半球中间坡度的地图。中斜率及其与比例的关系用于表征北半球测绘的一组地质单位的典型千米级粗糙度。该分析表明，许多单独的单元和单元组的特征在于独特的表面坡度，并且这些特征差异很大，它们有望用于单元的定义和表征。地质单元的坡度特性表征为解释其起源和演化提供了有用的信息。例如，多样的瓦斯提塔斯北极星形成亚单位的总体上光滑的地形主要由维京图像中几乎无法区分的约3 km，0.3度陡峭特征所主导。该单元的粗糙度特征与火星上其他地质单元的粗糙度特征不同，并暗示了所有子单元共同的千米尺度地形形成和/或修改的一些独特过程。几个高原高原单元的粗糙度特征的相似性表明，千米级地形很大程度上是从轰炸时期继承而来的。小范围内，北极帽和分层地形在很大程度上非常平坦。比较火星北半球主要地形类型的斜率-频率分布的长而陡峭的尾巴，并与地球各大陆进行比较。在北部低地发现的Vastitas Borealis组与火山口的高地和火山平原明显不同，后两个单元可以根据中位坡度相互区分。陆地比起坑洼的高地要光滑，但要比瓦斯蒂塔斯北欧气层和大多数火山平原要粗糙。列出了所有观察到的坡度都比休止角陡得多的坡度。陡峭的斜坡出现在构造陡峭的上部，最有可能代表基岩暴露。推测是易延展的极地盖中存在极其陡峭的斜坡，为这些斜坡的地质新近和/或正在进行的形成提供了证据。

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