Title: The composition of Solar system asteroids and Earth/Mars moons, and the Earth-Moon composition similarity,
Abstract: [abridged] In the typical giant-impact scenario for the Moon formation most
of the Moon's material originates from the impactor. Any Earth-impactor
composition difference should, therefore, correspond to a comparable Earth-Moon
composition difference. Analysis of Moon rocks shows a close Earth-Moon
composition similarity, posing a challenge for the giant-impact scenario, given
that impactors were thought to significantly differ in composition from the
planets they impact. Here we use a large set of 140 simulations to show that
the composition of impactors could be very similar to that of the planets they
impact; in $4.9\%$-$18.2\%$ ($1.9\%$-$6.7\%$) of the cases the resulting
composition of the Moon is consistent with the observations of
$\Delta^{17}O<15$ ($\Delta^{17}O<6$ ppm). These findings suggest that the
Earth-Moon composition similarity could be resolved as to arise from the
primordial Earth-impactor composition similarity. Note that although we find
the likelihood for the suggested competing model of very high mass-ratio
impacts (producing significant Earth-impactor composition mixing) is comparable
($<6.7\%$), this scenario also requires additional fine-tuned requirements of a
very fast spinning Earth. Using the same simulations we also explore the
composition of giant-impact formed Mars-moons as well as Vesta-like asteroids.
We find that the Mars-moon composition difference should be large, but smaller
than expected if the moons are captured asteroids. Finally, we find that the
left-over planetesimals ('asteroids') in our simulations are frequently
scattered far away from their initial positions, thus potentially explaining
the mismatch between the current position and composition of the Vesta
asteroid.