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题目材料：
No simple physical principle tells us whether planets should be rare or common. Monistic theories, in which planet and star formation are closely related, predicted that planets should be ubiquitous; an example was Laplace's nebular theory. In contrast, dualistic theories held that planets arise from events distinct from star formation, most of which were extremely unlikely. An example was tidal theory, wherein planets condense from material stripped away from a star during a chance encounter with another star, predicted to occur with a probability of only ~$$10^{-10}$$ for a given star. Doppler, transit, and microlensing techniques have shown that planets are prevalent, supporting the currently favored theory of planet formation in which planets condense from small particles within the gaseous disks that surround all young stars.
以上解析由 考满分老师提供。
