：火星表面!在
The surface of Mars
Another prominent feature of Mars’s surface is cratering. The Mariner spacecraft found that the surface of Mars, as well as that of its two moons, is pitted with impact craters formed by meteoroids falling in from space. As on our Moon, the smaller craters are often filled with surface matter-mostly dust-confirming that Mars is a dry desert world. However, Martian craters get filled in considerably faster than their lunar counterparts. On the Moon, ancient craters less than 100 meters across (corresponding to depths of about 20 meters) have been obliterated, primarily by meteoritic erosion. On Mars, there are relatively few craters less than 5 kilometers in diameter. The Martian atmosphere is an efficient erosive agent, with Martian winds transporting dust from place to place and erasing surface features much faster than meteoritic impacts alone can obliterate them.
火星表面的另一个突出特征是陨石坑。水手计划中的宇宙飞船发现在火星表面布满来自太空的流星撞击表面形成的陨石坑，火星的两颗卫星也是如此。与我们的月球类似，那些较小的陨石坑经常被一些物质填满(主要是灰尘)，这表明火星是一个干燥的沙漠世界。然而，与月球相比，火星上的陨石坑被填满的速度明显要快很多。在月球上，那些直径不足100米(对应深度大约在20米)的古老陨石坑主要因流星冲击而形成的尘埃的缘故而被填平了。而在火星上，只有相当少的一部分陨石坑直径小于5千米。火星大气是一种强效的腐蚀剂，加之火星上的风把灰尘从一个地方卷到另一个地方，较之仅仅是因流星冲击而形成的尘埃的作用，(火星上的)地表特征被消除得更快。
As on the Moon, the extent of large impact cratering (i.e. craters too big to have been filled in by erosion since they were formed) serves as an age indicator for the Martian surface. Age estimates ranging from four billion years for Mars’s southern highlands to a few hundred million years in the youngest volcanic areas were obtained in this way.
与在我们的月球上相同，那些巨大陨石坑的范围(例如，那些巨大到自形成后尚未被尘埃填满的陨石坑)充当着火星表面年龄指示器的角色。从火星南部高地的40亿年至最年轻的火山地区的几千万年都是用同样的方法估算的。
The detailed appearance of Martian impact craters provides an important piece of information about conditions just below the planet’s surface. Martian craters are surrounded by ejecta (debris formed as a result of an impact) that looks quite different from its lunar counterparts. A comparison of the Copernicus crater on the Moon with the (fairly typical) crater Yuty on Mars demonstrates the differences. The ejecta surrounding the lunar crater is just what one would expect from an explosion ejecting a large volume of dust, soil, and boulders. However, the ejecta on Mars gives the distinct impression of a liquid that has splashed or flowed out of crater. Geologists think that this fluidized ejecta crater indicates that a layer of permafrost, or water ice, lies just a few meters under the surface. Explosive impacts heated and liquefied the ice, resulting in the fluid appearance of the ejecta.
火星表面陨石坑的具体外貌为揭示该行星表面状况提供了非常重要的信息。火星陨石坑周边布满了喷出物(因撞击而形成的碎片)，这与月球上的陨石坑看起来非常不同。对比月球上的哥白尼陨石坑与火星上(相当典型的)尤蒂陨石坑可以看出不同。月球上陨石坑周边的喷出物正如我们以为的那样，一场爆炸喷出的大量的灰尘、土壤和岩石。然而，火星(上的陨石坑周边的)喷出物则因飞溅而出或溢出的液体给人留下了深刻的印象。地质学家认为这种具有流体化喷出物的陨石坑指示了在火星地表下几米处存在永冻土层或水冰。爆炸性的撞击加热并液化了这些冰，结果导致这些喷出物呈现流体状的特征。
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