Example of a typical simulation that results in a merger. Evolution over time is shown for (a) semimajor axis, (b) period ratio, (c) eccentricity, and (d) inclination. The initial mass of the inner (blue) and outer (green) moonlets is 0.26 and 0.32 M_l (lunar masses), respectively. The rotational period and obliquity of the proto-Earth is shown in orange in subplots (a) and (d). Initially, the inner moonlet migrates outward at a faster rate than the outer moonlet, as expected. However, the inner moonlet is relatively quickly captured into a 6:1 resonance with the outer moonlet. This increases the eccentricity and migration rate of the outer moonlet. Despite the outer moonlet’s faster migration rate relative to the inner moonlet, the increased eccentricity of the outer moonlet leads to a collision at ∼4.5 kyr. After the merger, the resulting 0.58 M_l moonlet tidally evolves outward (not shown).