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By Karen Nikos-Rose on September 30, 2019

A new explanation for the moon’s origin has that the moon formed inside the earth, back when our planet was a spinning cloud of vaporized rock called a synestia. The new model led by researchers at the University of California, Davis, and Harvard University resolves several questions about lunar formation and was published in the Journal of Geophysical Research — Planets.

"This new theory helps to explain the previously unexplainable."

— Sarah Stewart, professor of earth and planetary sciences, UC Davis. 

“The moon is chemically almost the same as the Earth, but with some differences,” Stewart said. “This is the first model that can match the pattern of the moon’s composition.” 

Current models of lunar formation suggest that the moon formed as a result of a glancing blow between the early Earth and a Mars-size body, commonly called Theia. According to the model, the collision between Earth and Theia threw molten rock and metal into orbit that collided together to make the moon.

The new theory relies instead on a synestia, a new type of planetary object proposed by Stewart and Simon Lock, graduate student at Harvard and visiting student at UC Davis, in 2017. A synestia forms when a collision between planet-sized objects results in a rapidly spinning mass of molten and vaporized rock with part of the body in orbit around itself. The whole object puffs out into a giant donut of vaporized rock.

Synestias condense into planets

Synestias likely don’t last long — perhaps only hundreds of years. They shrink rapidly as they radiate heat, causing rock vapor to condense into liquid, finally collapsing into a molten planet.

“Our model starts with a collision that forms a synestia,” Lock said. “The moon forms inside the vaporized Earth at temperatures of four to six thousand degrees Fahrenheit and pressures of tens of atmospheres.”

Want to know more? Read the full story on the research here.

Watch the UC Davis Facebook Live event, below, where Stewart answers questions about the impact the Apollo missions had on the science of understanding our universe.