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A large spinning hunk of hot, vaporized rock that forms when rocky, planet-sized objects collide
Earth may have taken on a jelly doughnut shape early in its history. The rocky planet was spinning through space about 4.5 billion years ago when it smacked into a Mars-sized hunk of rotating rock called Theia, according to one theory (SN: 4/15/17, p. 18). That hit may have turned Earth into a synestia, a blob of mostly vaporized rock with an indented center, resembling a slightly squished jelly doughnut, new simulations suggest. This synestia wouldn’t have had much of a solid or liquid surface. And the structure could have spread to about 100,000 kilometers across or more, much larger than its original 13,000 kilometers or so. The added girth would have come from rock vaporizing and continuing to spin quickly, which would puff up and flatten the shape.