Lunar-forming impacts: processes and alternatives
#MMPMID25114302
Canup RM
Philos Trans A Math Phys Eng Sci
2014[Sep]; 372
(2024
): 20130175
PMID25114302
show ga
The formation of a protolunar disc by a giant impact with the early Earth is
discussed, focusing on two classes of impacts: (i) canonical impacts, in which a
Mars-sized impactor produces a planet-disc system whose angular momentum is
comparable to that in the current Earth and Moon, and (ii) high-angular-momentum
impacts, which produce a system whose angular momentum is approximately a factor
of 2 larger than that in the current Earth and Moon. In (i), the disc originates
primarily from impactor-derived material and thus is expected to have an initial
composition distinct from that of the Earth's mantle. In (ii), a hotter, more
compact initial disc is produced with a silicate composition that can be nearly
identical to that of the silicate Earth. Both scenarios require subsequent
processes for consistency with the current Earth and Moon: disc-planet
compositional equilibration in the case of (i), or large-scale angular momentum
loss during capture of the newly formed Moon into the evection resonance with the
Sun in the case of (ii).
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