The Moon is a bit of a mystery (Picture: Getty/500px)
The Moon turned itself inside out after breaking off from the Earth, according to scientists.
How our satellite formed has puzzled astronomers for centuries, but the leading theory today suggests that during the late stages of Earth’s growth – around 4.5 billion years ago – another planet, Theia, smashed into it.
Known as the ‘giant impact’, it flung molten rock into space, which gradually merged together and eventually cooled, forming the Moon we see today.
Now, researchers have combined computer simulations and data to show how oceans of magma sank and rose to the Moon’s surface again over billions of years to form its current layers.
Think a giant lava lamp in the sky.
Astronomers say these magma oceans fluctuated over thousands of years due to gravitational instability.
The American research team say their findings, published in Nature Geoscience, could offer important insights into the evolution of our moon – and even potentially for planets such as the Earth and Mars.
Apollo astronauts brought back Moon rocks for astronauts to study (Picture: NASA/SWNS)
Most of our knowledge about the origins of the Moon comes from analysis of rock samples collected by Apollo astronauts more than 50 years ago, combined with theoretical models.
Samples of basaltic lava rocks from the surface showed surprisingly high concentrations of titanium, and later satellite observations found that these titanium-rich volcanic rocks are primarily located on the Moon’s nearside.
But how and why they got there has remained a mystery, until now.
The Moon formed fast and hot, and was likely covered by a global magma ocean.
As the molten rock gradually cooled and solidified, it formed the Moon’s mantle and the bright crust we see when we look up at a full moon at night.
But below the surface, the young moon was wildly out of equilibrium.
Models suggest that the last dregs of the magma ocean crystallised into dense minerals including ilmenite, a mineral containing titanium and iron.
Weigang Liang, who led the research at the University of Arizona’s Lunar and Planetary Laboratory (LPL), said: ‘Because these heavy minerals are denser than the mantle underneath, you would expect this layer to sink deeper into the Moon’s interior.’
Although the magma initially cooled and sank inwards, some of it melted again and popped back up (Picture: Adrien Broquet/University of Arizone)
In the millennia that followed that dense material did sink into the interior and mix with the mantle, but then melted and returned to the surface as the titanium-rich lava flows that we see on the surface today as the Moon’s seas, or mare.
‘Our moon literally turned itself inside out,’ said co-author Dr Jeff Andrews-Hanna, an associate professor at LPL.
But how and when this happened has been up for debate.
Using data from Nasa’s gravity recovery and interior laboratory (Grail) mission, in which two spacecraft orbited the Moon between 2011 and 2012, the team was able to measure tiny variations in its gravitational pull.
These showed that the titanium-rich layers migrated to the Moon’s nearside, which can be seen from Earth, and sank in ‘sheetlike cascades’.
And thanks to impact craters on the Moon providing a timeline of events on the surface, they also determined this happened at least 4.22 billion years ago.
Mr Liang added that research such as this could assist astronauts on upcoming manned missions to the Moon.
‘When the Artemis astronauts eventually land on the Moon to begin a new era of human exploration, we will have a very different understanding of our neighbour than we did when the Apollo astronauts first set foot on it,’ he said.
In November, a new study argued that pieces of Theia, the planet that smashed into Earth and chipped off the Moon, are still buried within our planet, and behave strangely during earthquakes.