Earth might once have resembled a hot, steamy doughnut

The newly proposed planetary shape is called a synestia

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.

If Earth went through a synestia state, it was short-lived. An object Earth’s size would have quickly cooled and condensed back into a solid, spherical rock in 100 to 1,000 years, researchers write online May 22 in the Journal of Geophysical Research: Planets. Rocky bodies may become synestias several times before settling into a permanent planet shape, say planetary scientists Simon Lock of Harvard University and Sarah Stewart of the University of California, Davis. They came up with the term synestia from syn-, meaning together, and Hestia, the Greek goddess of home, hearth and architecture.

No one has seen a synestia in space. But the weird structures could be out there, waiting to be discovered in solar systems far away.