Early Earth may have been a hot doughnut | Science News for Students

Early Earth may have been a hot doughnut

Our planet may have spent part of its violent infancy as a geological ‘jelly doughnut’
Aug 11, 2017 — 7:22 am EST
donut Earth

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).


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.

Power Words

(more about Power Words)

celestial     (in astronomy) Of or relating to the sky, or outer space.

centrifugal force     A force that seems to pull a rotating body — or something on a rotating object (such as a rider of an amusement park ride) — away from the center of rotation.

computer model     A software program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

cosmic     An adjective that refers to the cosmos — the universe and everything within it.

diameter     The length of a straight line that runs through the center of a circle or spherical object, starting at the edge on one side and ending at the edge on the far side.

geological     Adjective to describe things related to Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject.

Mars     The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.

mass     A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.

moon     The natural satellite of any planet.

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood.

semi     An adjective meaning “somewhat.”

shard     A piece of broken pottery, tile or rock, or a hard, broken piece of anything that has an irregular shape.

solar system     The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

synestia     (adj. synestic) The somewhat flattened, jelly-doughnut-like shape that some planetary scientists suspect Earth may have developed after undergoing a violent collision early in its infancy. Simon Lock of Harvard University in Cambridge, Mass., and Sarah Stewart at the University of California, Davis, came up with the term, itself a mashup of syn- (meaning together) and Hestia, the Greek goddess of home, hearth and architecture.

Theia     (in astronomy) The name of a hypothetical protoplanet, named for the Greek goddess of sight, who was also the supposed mother of the moon goddess Selene. If this protoplanet existed, the Mars-sized rocky world would have died in a violent collision with Earth, some 4.5 billion years ago. Part of the debris from it — and Earth — might have eventually collected to form a new celestial object: Earth’s moon.


Journal:​ S.J. Lock and S.T. Stewart. The structure of terrestrial bodies: Impact heating, corotation limits, and synestiasJournal of Geophysical Research: Planets. Published online May 22, 2017. doi: 10.1002/2016JE005239.