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takyon writes:

The Moon may have formed from the same synestia (spinning donut shape) as Earth rather than through a collision between the early Earth and the hypothetical protoplanet Theia:

Making the moon: Study details new story for how the moon formed

A graduate student in Harvard's Department of Earth and Planetary Sciences, [Simon] Lock is the lead author of a study that suggests the Moon - rather than being spun out of the aftermath of a collision - emerged from a massive, donut-shaped cloud of vaporized rock called a synestia. Along with Lock, the study, published February 28 in Journal of Geophysical Research: Planets, is co-authored by Sarah Stewart (UC Davis), Michail Petaev (Harvard), Zoë Leinhardt (Bristol), Mia Mace (Bristol), Stein Jacobsen (Harvard), and Matija Ćuk (SETI).

"The commonly accepted theory as to how the Moon was formed is that a Mars sized body collided with the proto-Earth and spun material into orbit," Lock said. "That mass settled into a disk and later accreted to form the moon. The body that was left after the impact was the Earth. This has been the canonical model for about 20 years." It's a compelling story, Lock said, and it's also probably not correct. "Getting enough mass into orbit in the canonical scenario is actually very difficult, and there's a very narrow range of collisions that might be able to do it," he said. "There's only a couple of degree window of impact angles and a very narrow range of sizes...and even then some impacts still don't work."

"This new work explains features of the Moon that are hard to resolve with current ideas," said Stewart, a professor of Earth and Planetary Sciences at UC Davis. "This is the first model that can match the pattern of the Moon's composition."

The origin of the Moon within a terrestrial synestia (DOI: 10.1002/2017JE005333) (DX)

Previously: "Synestia" Phase of Planetary Formation Simulated

Original Submission