FIG. 2.

The precession rates for Earth-like planets 4.52 billion years after a moon-forming impact. Axes show the total angular momentum and lunar mass resulting from the impact and are normalized by the true values for the actual Earth-Moon system. Note that a moderately different angular momentum, or lunar mass, results in either an unstable obliquity (where precession <26″/y) or more rapid precession than that of the true Earth (i.e., >50″/y). Thus, the actual Earth-Moon properties are apparently fine-tuned to give slow Milankovitch cycles. For further details see Waltham (2004).