Hydrocode simulation of Ganymede and Europa cratering trends - How thick is Europa's crust?
Hydrocode simulation of Ganymede and Europa cratering trends - How thick is Europa's crust?
复制标题
木卫三和木卫二陨石坑趋势的水电编码模拟 - 木卫二的地壳有多厚？
DOI：
10.1016/j.icarus.2013.12.009
复制
发表时间：
2014
期刊：
影响因子：
3.2
通讯作者：
Bray V
中科院分区：
文献类型：
--
作者：
Bray V
外太阳系研究的一个持续争论的焦点是木卫二冰壳的厚度，因为它影响了其地下海洋的可居住性和可访问性。在这里，我们使用水文模拟的影响过程中分层冰和水的目标和比较欧罗巴陨石坑的趋势和伽利略派生的地形剖面调查地壳厚度。在冰厚度小于抛射体半径14倍的模拟中，撞击物完全或部分穿透冰壳。在这些薄壳模拟中产生的陨石坑始终小于较大冰厚度的陨石坑，这将使大型撞击物数量的推断复杂化。在模拟中，由此产生的陨石坑是冰层厚度的3倍，导致了山顶坑的形态。这项工作支持了在岩石和冰体上发现的山顶坑陨石坑，可以由深度较弱的层产生。我们认为，地板坑，只看到富含冰的机构，需要一个不同的形成机制，以首脑pits.Pristine陨石坑中形成的高热流的目标比相同的影响到一个目标的热流较小，这表明“启动”陨石坑形态的粘性松弛，均衡rerereadjustment和侵蚀速率的研究是不同的陨石坑形成在不同的热流的时间。我们发现，只有当模拟撞击到7公里深的上层脆性冰层时，才能重现欧罗巴的陨石坑深度-直径趋势，相应的地热梯度为0.025 K/m。由于冰的厚度估计低于1000公里，这项工作的结果表明，木卫二表面冰的对流翻转可能发生，或者已经发生，使土著生命的发展成为可能。
One of the continuing debates of outer Solar System research centers on the thickness of Europa’s ice crust, as it affects both the habitability and accessibility of its sub-surface ocean. Here we use hydrocode modeling of the impact process in layered ice and water targets and comparison to Europan cratering trends and Galileo-derived topographic profiles to investigate the crustal thickness. Full or partial penetration of the ice crust by an impactor occurred in simulations in which the ice thickness was less than 14 times the projectile radius. Craters produced in these thin-shell simulations were consistently smaller than for larger ice thicknesses, which will complicate inference of large impactor population sizes. Simulations in which the resultant crater was 3 times the ice layer thickness resulted in summit-pit morphology. This work supports that summit pit craters noted on both rocky and icy bodies, can be created by the presence of a weaker layer at depth. We suggest that floor pits, seen only on ice-rich bodies, require a different formation mechanism to summit pits.Pristine craters formed in a target with high heat flow were shallower than for the same impact into a target of lesser heat flow, suggesting that the ‘starting’ crater morphology for viscous relaxation, isostatic readjustments and erosion rate studies is different for craters formed in times of different heat flow. We find that the crater depth–diameter trend of Europa can only be recreated when simulating impact into an upper brittle ice layer of 7 km depth, with a corresponding geothermal gradient of 0.025 K/m. As this ice thickness estimate is below ∼10 km, results from this work suggest that convective overturn of the surface ice may occur, or have occurred, on Europa making the development of indigenous life a possibility.