Swiss researchers uncover clues to moon's origins

The moon is curiously large in proportion to Earth, a phenomenon that has long stumped scientists Keystone

New findings by Bern University researchers suggest that the moon may have been formed in a high-velocity hit-and-run collision, a theory which explains the presence of Earth-like elements on the moon.

This content was published on August 30, 2012 - 14:09
Chantal Britt,

It is widely accepted that the Earth’s moon formed 4.5 billion years ago from an impact between the Earth and a celestial object the size of Mars called Theia.

While simulations of the collision done over past decades suggested that the moon would have mostly been formed by material from Theia, the oxygen isotopes found on the moon are, mysteriously, exactly the same as those found on Earth. This mystery is known as the “lunar paradox”.

“Our model took into account relatively faster velocities than previous models,” Willy Benz, head of the Space Research and Planetary Science group and co-author of the study, told

“With our new approach we were able to show that more material from Earth would end up in the moon if the impact had been faster than previously assumed. This would explain the similarity of certain elements on the Earth and the moon.”

Probes on the moon have shown that it is made up of materials very similar to those composing the Earth’s crust and mantle, but not quite the same. With slower minimal velocities, most of the material in a collision between the Earth and Theia comes from the projectile, Benz said.

However, when the collision is modelled at a faster velocity, more of the Earth’s materials and chemical elements end up in the lunar make-up. Furthermore, a higher speed may also change where the projectile originally came from, he explained.

“If you assume a higher velocity, the celestial body may have come from much further away in the solar system; it could have contained more ice than rock."

Possible breakthrough

“While none of the simulations presented in their research provides a perfect match for the constraints from the actual Earth-Moon-system, several do come close," Alessandro Morbidelli, an editor of the Icarus journal, which published the study, wrote in a statement.

“This work, therefore…may finally lead to the long-searched solution of the lunar paradox.”

The Earth’s moon has puzzled scientists for years. Compared with other moons orbiting other planets including Jupiter, Saturn and Uranus, it has a mass ratio of one to 81, meaning it is much larger compared with the Earth than the moons of other planets, where the ratio is closer to one to 10,000.

“These findings are important because they’re opening up more doors and help us better understand the moon,” Benz told

“We believe that if you better understand the history of the moon, then you will also better understand the Earth.“

Swiss Space

Switzerland was one the founders of the European Space Agency.

The Swiss space industry includes 28 research institutes and 54 companies.

They specialise mostly in ground equipment, optical apparatuses, telecommunications systems, clocks, robotic machinery, microgravity research and weather surveillance.

Switzerland's Claude Nicollier is an astrophysicist, test pilot and astronaut.

He was the first foreigner granted mission specialist status by Nasa and completed four missions on board the space shuttle. His first shuttle mission was with the Atlantis.

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