The collision model – Young proto-Earth, Theia & the Moon

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Editor’s summary

The Moon is thought to have formed mainly from material within a giant impactor that struck the proto-Earth, so it seems odd that the compositions of the Moon and Earth are so similar, given the differing composition of other Solar System bodies. Alessandra Mastrobuono-Battisti et al. track the feeding zones of growing planets in a suite of computational simulations of planetary accretion and find that different planets formed in the same simulation have distinct compositions, but the compositions of giant impactors are more similar to the planets they impact. A significant fraction of planet–impactor pairs have virtually identical compositions. The authors conclude that the similarity in composition between the Earth and Moon could be a natural consequence of a late giant impact.

Paper:

A primordial origin for the compositional similarity between the Earth and the Moon

Alessandra Mastrobuono-Battisti, Hagai B. Perets & Sean N. Raymond
AffiliationsContributionsCorresponding authors
Nature 520, 212–215 (09 April 2015) doi:10.1038/nature14333
Received 10 November 2014 Accepted 10 February 2015

http://www.nature.com/nature/journal/v520/n7546/abs/nature14333.html

Most of the properties of the Earth–Moon system can be explained
by a collision between a planetary embryo (giant impactor) and the
growing Earth late in the accretion process1–3. Simulations show that
most of the material that eventually aggregates to form the Moon
originates from theimpactor1,4,5. However, analysis of the terrestrial
and lunar isotopic compositions show them to be highly similar6–11.
In contrast, the compositions of other Solar System bodies are significantly
different from those of the Earth and Moon 12–14, suggesting
that different Solar System bodies have distinct compositions. This
challenges the giant impact scenario, because the Moon-forming
impactor must then also be thought to have a composition different
from that of the proto-Earth. Here we track the feeding zones of
growing planets in a suite of simulations of planetary accretion 15, to
measure the composition of Moon-forming impactors.We find that
different planets formed in the same simulation have distinct compositions,
but the compositions of giant impactors are statistically
more similar to the planets they impact. A large fraction of planet–
impactor pairs have almost identical compositions. Thus, the similarityin
composition between the Earth and Moon could be a natural
consequence of a late giant impact.

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