Paper
Forming a Moon with an Earth-like Composition via a Giant Impact
Published Nov 23, 2012 · R. Canup
Science
510
Citations
73
Influential Citations
Abstract
Forming the Moon from Earth It is thought that the Moon formed after a Mars-sized planet hit Earth about 4.5 billion years ago. Computer simulations of this event predict that the Moon was produced primarily from material from the impacting planet. However, the Moon has a similar composition to that of Earth, and the impacting planet would likely have had a different composition. Prior models assumed that the impact left the Earth-Moon system with the same angular momentum as it has today (see the Perspective by Halliday). Ćuk and Stewart (p. 1047, published online 17 October; see the cover) show that the angular momentum of the Earth-Moon system could have decreased by half after the Moon-forming impact, opening the door to new impact models. For example, simulations suggest that high-velocity impacts onto a fast-spinning early Earth can lead to a Moon formed primarily from Earth's mantle. Canup (p. 1052, published online 17 October) considered instead lower-velocity impacts by planets comparable in mass to the proto-Earth, which could generate a Moon and an Earth with similar compositions. Computer simulations show that a giant impact on early Earth could lead to a Moon with a composition similar to Earth’s. In the giant impact theory, the Moon formed from debris ejected into an Earth-orbiting disk by the collision of a large planet with the early Earth. Prior impact simulations predict that much of the disk material originates from the colliding planet. However, Earth and the Moon have essentially identical oxygen isotope compositions. This has been a challenge for the impact theory, because the impactor’s composition would have likely differed from that of Earth. We simulated impacts involving larger impactors than previously considered. We show that these can produce a disk with the same composition as the planet’s mantle, consistent with Earth-Moon compositional similarities. Such impacts require subsequent removal of angular momentum from the Earth-Moon system through a resonance with the Sun as recently proposed.
Highly CitedA giant impact on early Earth could lead to a Moon with a composition similar to Earth's, potentially forming a moon from Earth's mantle.
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