Martian craters viewed by the Thermal Emission Imaging System instrument: Double‐layered ejecta craters
Martian craters viewed by the Thermal Emission Imaging System instrument: Double‐layered ejecta craters
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热发射成像系统仪器观察到的火星陨石坑：双层喷射物陨石坑
DOI：
10.1029/2005je002638
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发表时间：
2006
影响因子：
--
通讯作者：
P. Mouginis
中科院分区：
文献类型：
--
作者：
J. Boyce;P. Mouginis
热发射成像系统（THEMIS）的可见光（VIS）图像为了解火星陨石坑独特的喷出物沉积物的性质和发展提供了新的见解。本研究的重点是双层喷射陨石坑（DLE）。迄今为止，主要使用THEMIS VIS数据检查了100多个mid陨石坑。我们的观测结果表明，DLE陨石坑喷射物的就位分两个阶段，内部喷射层的就位与单层喷射物（SLE）陨石坑喷射物相似。这可能涉及到弹道过程和流动过程。相比之下，DLE陨石坑的外层喷射层似乎是通过推进的喷射幕或基底涌浪产生的龙卷风产生的物质的高速流出而放置的。值得注意的是，DLE陨石坑缺乏次级陨石坑，这表明通常产生这种陨石坑的大型喷射块可能被这些风带走和/或压碎，或者由于目标物质中存在水而破碎。这些观测结果表明，挥发物（无论是被困在地下还是在大气中）在DLE陨石坑的喷出物的安置中发挥了关键作用，并留下了挥发物在其他类型流化陨石坑（即SLE和MLE陨石坑）的喷出物的安置中起什么作用的问题。由于DLE陨石坑位于火星的许多不同区域，通常与其他类型的陨石坑非常接近，因此产生DLE陨石坑的条件（例如大气密度）必须波动，或者火星地壳必须出乎意料地不均匀（横向和垂直）。虽然异质性的程度尚未得到确认，但最近关于火星可能发生气候变化的建议提出了撞击目标物质的可能性，这些物质周期性潮湿，或者周期性存在明显更高的大气压力。
[1] The Thermal Emission Imaging System (THEMIS) visible (VIS) images provide new insight into the nature and development of the unique ejecta deposits of Martian craters. This study focuses on double-layered ejecta (DLE) craters. To date, over 100 DLE craters have been examined using mainly THEMIS VIS data. Our observations suggest that emplacement of DLE crater ejecta occurred in two stages, with the inner ejecta layer emplaced similar to single-layered ejecta (SLE) crater ejecta. This may have involved both ballistic and flow processes. In contrast, the outer ejecta layer of DLE craters appears to have been emplaced through the high-velocity outflow of materials from tornadic winds generated by the advancing ejecta curtain or base surge. Remarkably, DLE craters lack secondary craters, which suggests that the large ejecta blocks that normally produce such craters may have either been entrained and/or crushed by these winds or fragmented as a result of the presence of water in the target materials. These observations suggest that volatiles (either trapped in the subsurface or in the atmosphere) have played a key role in the emplacement of the ejecta of DLE craters and leaves open the question as to what role volatiles play in the emplacement of ejecta of other types of fluidized ejecta craters (i.e., SLE and MLE craters). Because DLE craters are found in many different regions of Mars, often in close proximity to other types of craters, conditions (e.g., atmospheric density) that produce DLE craters must fluctuate or the Martian crust must be unexpectedly heterogeneous (laterally and vertically). While the degree of heterogeneity has yet to be recognized, recent suggestions about possible Martian climate change raises the possibility of impact into target materials that are periodically wet or that a significantly higher atmospheric pressure may be periodically present.