Strom Robert G, Chapman Clark R, Merline William J, Solomon Sean C, Head James W
Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.
Science. 2008 Jul 4;321(5885):79-81. doi: 10.1126/science.1159317.
Morphologies and size-frequency distributions of impact craters on Mercury imaged during MESSENGER's first flyby elucidate the planet's geological history. Plains interior to the Caloris basin displaying color and albedo contrasts have comparable crater densities and therefore similar ages. Smooth plains exterior to Caloris exhibit a crater density approximately 40% less than on interior plains and are thus volcanic and not Caloris impact ejecta. The size distribution of smooth-plains craters matches that of lunar craters postdating the Late Heavy Bombardment, implying that the plains formed no earlier than 3.8 billion years ago (Ga). At diameters less than or equal to 8 to 10 kilometers, secondary impact craters on Mercury are more abundant than primaries; this transition diameter is much larger than that on the Moon or Mars. A low density of craters on the peak-ring basin Raditladi implies that it may be younger than 1 Ga.
信使号首次飞越水星期间拍摄的撞击坑的形态和大小频率分布揭示了该行星的地质历史。卡洛里斯盆地内部的平原呈现出颜色和反照率对比，其撞击坑密度相当，因此年龄相似。卡洛里斯盆地外部的平滑平原撞击坑密度比内部平原低约40%，因此是火山成因的，而非卡洛里斯撞击喷出物。平滑平原上撞击坑的大小分布与晚期重轰炸期之后的月球撞击坑相匹配，这意味着这些平原形成时间不早于38亿年前（Ga）。在直径小于或等于8至10公里时，水星上的次生撞击坑比原生撞击坑更为丰富；这个转变直径比月球或火星上的要大得多。环形山盆地拉迪拉迪上的撞击坑密度较低，这表明它可能小于1 Ga。
