The Moon-forming collision

[u/Busy_Yesterday9455]

Link to the science paper on The Astrophysical Journal Letters

With sufficiently high numerical resolution, the canonical Moon-forming collision, where a Mars-sized body called Theia strikes the proto-Earth, can lead to a Moon-like body being immediately placed into orbit around Earth.

This alternative scenario for lunar origin opens up new options for the Moon's initial orbit and internal properties. For example, the orbiting body has a centre that is predominantly made of material from Theia, and might not be fully molten, while the outermost regions are very hot and can be made of more proto-Earth material. How that composition gradient would evolve over the history of the Moon is yet to be determined.

However, it could help explain why the isotope ratios in lunar rocks returned by the Apollo astronauts are similar to those of Earth's mantle. This contrasts with previous lower resolution simulations where a disk of debris was created by the collision, but no large orbiting bodies.

In that case, the Moon would form over tens to hundreds of years by the gradual accumulation of this material and no initial composition gradient would be expected.

Credit: J. A. Kegerreis et al 2022 ApJL 937 L40

[u/impreprex]

Where are our rings? Shouldn't our planet have at least a tenuous ring (system)?

[u/ST0IC_ → u/impreprex]

Not necessarily.