Marine‐target craters on Mars? An assessment study
Marine‐target craters on Mars? An assessment study
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火星上的海洋目标陨石坑评估研究？
DOI：
10.1111/j.1945-5100.2004.tb00344.x
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发表时间：
2004
影响因子：
2.2
通讯作者：
A. Fairén
中科院分区：
文献类型：
--
作者：
J. Ormö;J. Dohm;J. Ferris;A. Lepinette;A. Fairén
摘要：对地球上撞击坑的观测表明，目标处的水柱强烈影响撞击坑的岩性和形态。影响程度随目标水深和冲击器直径的不同而变化。卫星图像中可检测到的形态特征包括同心形状，内火山口嵌入较浅的外火山口内，外火山口是由水流涌动开出的沟壑切割而成。在这项研究中，我们表明，如果火星上存在海洋、大海和湖泊一段时间，那么海洋目标陨石坑一定已经形成。我们根据“接触点1和接触点2”内假定海洋的水深、范围和持续时间、不同海洋阶段的陨石坑速率以及在海洋海底形成持久陨石坑所需的最小撞击器直径的计算机模型，对此类陨石坑的最小和最大数量进行了评估。我们还讨论了侵蚀和沉积对陨石坑保存和暴露的影响。对于持续时间为 100,000 年的较小“接触 2”内的海洋以及当前陨石坑形成率较低的情况，仅会形成约 1-2 个可检测到的海洋目标陨石坑。据估计，持续时间为 0.8 戈里时，可能会形成多达 1400 个陨石坑。尽管在 3.5 Gyr 之前估计陨石坑形成率较高，但持续时间为 100,000 年的较大“接触 1-Meridiani”内的海洋不会出现任何海底陨石坑。另一方面，最长持续时间为 0.8 戈里，可能会形成约 160 个海底陨石坑。然而，陆地实例表明，大多数海洋目标陨石坑可能被厚厚的沉积物覆盖。欧洲航天局火星快车和美国国家航空航天局 2005 年任务计划进行的探地雷达勘测可能会发现埋藏的陨石坑，但尚不确定该分辨率是否能够检测海洋目标陨石坑的诊断特征。在火星上发现海洋目标陨石坑的意义并非没有意义，因为此类发现将有助于解决关于大型水体是否占据火星北部平原的持续争论，并有助于限制未来的古气候重建。
Abstract— Observations of impact craters on Earth show that a water column at the target strongly influences lithology and morphology of the resultant crater. The degree of influence varies with the target water depth and impactor diameter. Morphological features detectable in satellite imagery include a concentric shape with an inner crater inset within a shallower outer crater, which is cut by gullies excavated by the resurge of water. In this study, we show that if oceans, large seas, and lakes existed on Mars for periods of time, marine‐target craters must have formed. We make an assessment of the minimum and maximum amounts of such craters based on published data on water depths, extent, and duration of putative oceans within “contacts 1 and 2,” cratering rate during the different oceanic phases, and computer modeling of minimum impactor diameters required to form long‐lasting craters in the seafloor of the oceans. We also discuss the influence of erosion and sedimentation on the preservation and exposure of the craters. For an ocean within the smaller “contact 2” with a duration of 100,000 yr and the low present crater formation rate, only ˜1–2 detectable marine‐target craters would have formed. In a maximum estimate with a duration of 0.8 Gyr, as many as 1400 craters may have formed. An ocean within the larger “contact 1‐Meridiani,” with a duration of 100,000 yr, would not have received any seafloor craters despite the higher crater formation rate estimated before 3.5 Gyr. On the other hand, with a maximum duration of 0.8 Gyr, about 160 seafloor craters may have formed. However, terrestrial examples show that most marine‐target craters may be covered by thick sediments. Ground penetrating radar surveys planned for the ESA Mars Express and NASA 2005 missions may reveal buried craters, though it is uncertain if the resolution will allow the detection of diagnostic features of marine‐target craters. The implications regarding the discovery of marine‐target craters on Mars is not without significance, as such discoveries would help address the ongoing debate of whether large water bodies occupied the northern plains of Mars and would help constrain future paleoclimatic reconstructions.