Mini-moons
DID MINI-MOONS MAKE THE EARTH?
A new theory suggests ‘moonfalls’ may have formed our planet’s first continents
Reported by Libby Plummer
© Tobias Roetsch
Mini-moons may have battered Earth with debris in its formative years, shaping the young planet and maybe even building the first continents.
That’s the theory put forward by a new study, turning the ‘giant-impact hypothesis’ on its head.
In the well-established giant-impact theory, a Mars-sized rocky object called Theia smashed into what would become Earth around 100 million years after the Solar System was formed. The giant collision spewed debris up into space, forming a disc of debris, some of which gradually came together to form our Moon.
This idea was initially put forward in 2012. Then, four years later, researchers at the University of California, Los Angeles (UCLA) published new evidence to cement the theory. While it was previously thought that the collision, which took place around 4.5 billion years ago, was a powerful, angled side-swipe by the giant rock Theia, the new evidence confirmed it was likely to have been a violent, head-on smash. The team came to this conclusion after analysing seven rocks brought back to Earth by the Apollo 12, 15 and 17 lunar missions, along with six volcanic rocks from the Earth’s mantle. A shared chemical signature in the oxygen atoms both in the Moon rocks and the Earth rocks made it likely that a head-on collision had occurred, the researchers concluded.
“Theia was thoroughly mixed into both the Earth and the Moon, and evenly dispersed between them,” said Edward Young, UCLA professor and lead author of the study, speaking at the time of its publication. “This explains why we don’t see a different signature of Theia in the Moon versus the Earth.” The study explains that the alternative, a glancing side blow from Theia, would have meant that the vast majority of the Moon would have been formed from Theia, and thus the Earth and Moon would have different chemical ‘fingerprints’.