论文标题
冲击火山口和古代火星海岸线的可观察性
Impact Craters and the Observability of Ancient Martian Shorelines
论文作者
论文摘要
数十年来，已经研究并辩论了火星北半球可能存在的早期海洋。早期的火星气候的本质仍然有些神秘，但是一个或多个早期海洋的证据意味着持久的可居住时期。支持早期海洋的主要证据是一组拟议的残留海岸线，这些海岸线围绕着地球的大部分。这些功能被认为年龄超过3.6 ga，可能年龄与4 GA一样古老，这将使它们成为火星表面仍然可以识别的最古老的大型大型特征。然而，一个尚未彻底解决的问题是，这种旧的海岸线是否可以在可识别形式的撞击火山口，构造，火山和水文学等破坏过程中生存下来。在这里，我们详细介绍了这些过程之一 - 影响碎屑。我们使用标准的火山口计数年龄模型来产生陨石坑的全球群体，并与假设的海岸线相交，并跟踪直接影响的海岸线部分。 The oldest shorelines (>= 4 Ga) are at least 70 % destroyed by direct impacts.当包括大于半径大于100 m的火山口的效果时，任何年龄> 3.6 GA的海岸线都被剖析到相对较短的不连续段不超过40 km。当排除小于500 m的陨石坑时，存活的节段长度可能大约1000 km。最古老的海岸线在撞击后表现出分形结构，作为一系列尺度上的线条集合。如果特征是真正的海岸线，高分辨率研究应发现相似的破坏和不连续性水平。但是，我们的结果表明，观察到像4 GA一样古老的海岸线是一个重大挑战，并引发了有关先前映射工作的问题。
The existence of possible early oceans in the northern hemisphere of Mars has been researched and debated for decades. The nature of the early martian climate is still somewhat mysterious, but evidence for one or more early oceans implies long-lasting periods of habitability. The primary evidence supporting early oceans is a set of proposed remnant shorelines circling large fractions of the planet. The features are thought to be older than 3.6 Ga and possibly as old as 4 Ga, which would make them some of the oldest large-scale features still identifiable on the surface of Mars. One question that has not been thoroughly addressed, however, is whether shorelines this old could survive modification and destruction processes like impact craters, tectonics, volcanism, and hydrology in recognizable form. Here we address one of these processes -- impact cratering -- in detail. We use standard crater counting age models to generate synthetic, global populations of craters and intersect them with hypothetical shorelines, tracking portions of the shoreline that are directly impacted. The oldest shorelines (>= 4 Ga) are at least 70 % destroyed by direct impacts. Shorelines of any age >3.6 Ga are dissected into relatively short, discontinuous segments no larger than about 40 km when including the effects of craters larger than 100 m in radius. When craters smaller than 500 m in radius are excluded, surviving segment lengths can be as large as ~1000 km. The oldest shorelines exhibit fractal structure after impacts, presenting as a discontinuous collection of lines over a range of scales. If the features are truly shorelines, high-resolution studies should find similar levels of destruction and discontinuity. However, our results indicate that observing shorelines as old as 4 Ga, should they exist, is a significant challenge and raises questions about prior mapping efforts.
