Planets

Early Earth may have been a hot doughnut

Our planet may have spent part of its violent infancy as a geological ‘jelly doughnut’

Artists’ illustration of synestia, a spinning disk of vaporized rock that looks like a jelly-filled doughnut with a small, solid core (here, in gray).

S. LOCK/HARVARD UNIV.

By Ashley Yeager

August 11, 2017 at 6:22 am

In its early youth, Earth might have spent some time shaped like a hot, spinning jelly doughnut. That’s a suggestion just offered up by two planetary scientists.

Doughnut Earth would have existed some 4.5 billion years ago. Back then, our rocky planet was spinning through space when it likely smacked into a Mars-sized hunk of rotating rock called Theia (THAY-ah). This, in fact, is one now-popular explanation for how our moon came to be. It was flung off as a rocky shard released by that collision.

That massive smashup may have turned Earth into a blob of mostly vaporized rock. And the planet’s center would likely have been indented, as if squeezed by cosmic fingers. A new computer modeling study came up with this likely shape. Simon Lock of Harvard University in Cambridge, Mass., and Sarah Stewart at the University of California, Davis, reported their computer’s new assessment May 22 in the Journal of Geophysical Research: Planets.

Lock and Stewart also came up with a new term to describe the geological-jelly-doughnut shape that Earth would have resembled. They call it synestia (Sih-NES-tee-uh), from syn- (meaning together) and Hestia, the Greek goddess of home, hearth and architecture.

The semi-flattened orb might have ballooned out to about 100,000 kilometers (or some 62,000 miles) across or more. Prior to the collision, Earth’s diameter had only been some 13,000 kilometers (8,000 miles) or so. Why the temporary, smooshed up shape? Much of Earth’s rock would have vaporized as it continued to spin quickly. Centrifugal force due to this spinning would have flattened the shape of the now-softened Earth.

If Earth went through a synestia state, it was short-lived. An object Earth’s size would have cooled quickly. This would have returned the planet back into a solid, spherical rock. It would likely have taken no more than 100 to 1,000 years to return to its former shape, Lock and Stewart conclude.

Rocky bodies may become synestic several times before settling into a permanent orb-like shape, they say. To date, however, no one has seen a synestia in space. But the weird structures could be out there, Lock and Stewart suggest. They might be awaiting discovery in solar systems far away.