Synestia

A synestia is a rapidly spinning donut-shaped mass of vaporized rock. In computer simulations of giant impacts of rotating objects a synestia can form if the total angular momentum is greater than the co-rotational limit.^[1] Beyond the co-rotational limit the velocity at the equator of a body would exceed the orbital velocity.^[2] In a synestia this results in an inner region rotating at a single rate with a loosely connected torus orbiting beyond it.^[3]

According to recent studies, synestia was an early-stage process for the formation of the Earth and Moon within the Giant-impact hypothesis. A synestia forms following a high energy, high angular momentum, giant impact. As the synestia cools droplets form in its outer layers and rain inward. Those that remain outside the roche limit of the inner region accrete to form moonlets and combine to form the moon. The Earth forms later once the synestia cools sufficiently to fall within the co-rotational limit. The formation of the Moon within a cloud of vapor results in it having similar isotopic ratios as the Earth. The later formation of the Earth (after the synestia cools) enables it to accrete more volatile elements than the Moon.^[4]

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