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题目材料：
One characteristic of terrestrial cratering is the presence of doublet craters: 3 of the 28 large impact craters on Earth (greater than 20 kilometers diameter) have partner craters. For example, the Kamensk crater in Russia, 25 kilometers in diameter, is partnered by the Gusev crater, 3 kilometers wide and of identical age. Since such doublets form when two well-separated asteroids impact Earth nearly simultaneously, their relatively frequent occurrence serves as evidence for the existence of a substantial population of co-orbiting asteroids.
Are other rocky planets subject to impacts from co-orbiting asteroids? Venus is a promising planet to search for doublets because its surface is young, erosion is nearly nonexistent, and its rater population is significantly larger than Earth's, but not so large that there is a high probability of chance associations. Researchers found that the proportion of doublet craters on Venus is significantly smaller than on Earth. However, Venus' denser atmosphere may screen out the smaller member of some asteroid pairs. If Earth had a similar screening effect, only one of its three known doublets would have formed, making the proportion of doublet craters on Earth(3.6%) identical to Venus'(2.2%) within uncertainties. The researchers concluded that co-orbiting asteroids must be common among both the near-Earth and near-Venus asteroid populations.
Are other rocky planets subject to impacts from co-orbiting asteroids? Venus is a promising planet to search for doublets because its surface is young, erosion is nearly nonexistent, and its rater population is significantly larger than Earth's, but not so large that there is a high probability of chance associations. Researchers found that the proportion of doublet craters on Venus is significantly smaller than on Earth. However, Venus' denser atmosphere may screen out the smaller member of some asteroid pairs. If Earth had a similar screening effect, only one of its three known doublets would have formed, making the proportion of doublet craters on Earth(3.6%) identical to Venus'(2.2%) within uncertainties. The researchers concluded that co-orbiting asteroids must be common among both the near-Earth and near-Venus asteroid populations.
以上解析由 考满分老师提供。
