Moon created by a ‘dust doughnut’ after Earth collided with baby planet

THE Moon was formed after early Earth collided with a baby planet, creating a “dust doughnut” which spat out the lunar satellite, scientists have suggested.

Up until now, experts thought the Moon formed as a result of a glancing blow between the early Earth and a Mars-size body, commonly called Theia. However, experts at Harvard University and the Universities of Bristol and California now think that the chances of that having happened are too slim to be plausible.

Instead, they have suggested that although early Earth was involved in a huge collision 4.5 billion years ago, it was so devastating that it vaporised both bodies, creating a seething, spinning doughnut-shaped cloud of dust and debris, called a synestia. The new theory suggests that chunks of molten rock were sent into orbit during the impact, creating a seed for the Moon.

Synestias only last a few hundred years, before shrinking rapidly, causing rock vapour to condense into liquid, which finally collapses into a molten planet.

The Moon, which would have grown from ejected rock flung on to it from the “whirling doughnut”, now became trapped in Earth’s orbit.

The new model, which was simulated on a computer, also explains why the Moon’s chemical composition is slightly different to that of Earth.

“This is the first model that can match the pattern of the Moon’s composition,” said Sarah Stewart, professor of Earth and Planetary Sciences at University of California, Davis. The research was published in the Journal of Geophysical Research – Planets.