A GINORMOUS crater on the Moon has left space scientists scratching their heads.

The pit on the lunar south pole covers the same area as the United States and stretches across nearly a quarter of the Moon – but experts have no idea how it got there.

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Known as the Aitken basin, scientists had long thought it was left behind by a huge collision with a very large, very fast meteor billions of years ago.

The impact cracked open the dark side of the Moon and scattered huge chunks of an inner layer known as the mantle across its surface, according to the theory.

However, a new study from researchers in China throws this idea into contention.

They looked at readings from China's Yutu-2 Moon rover, which landed in the Aitken basin alongside the country's Chang'e 4 lander in January.

3 Here are the different types of Moon rock found around the Aitken basin Credit: Nasa

After analysing six patches of soil from the bottom of the crater, the researchers argued it's largely made up of crust, and not mantle.

If true, this suggests the impact that opened up the Aitken basin did not hit hard enough to smear the Moon's innards across its surface.

"We are not seeing the mantle materials at the landing site as expected," said Dr Hao Zhang, a planetary scientist at the China University of Geosciences.

The findings showed that the Aitken basin was not formed by a high-speed meteor strike after all.

3 Researchers looked at readings from China's Yutu-2 Moon rover

Such a strike would almost certainly have spattered the Moon's surface with chunks of mantle that would still be there today.

The researchers refrained from taking a punt at what might have left the huge dent.

Other theories still back a meteorite collision as the most likely candidate.

However, instead of a full on smash, the strike may have merely glanced the Moon – enough to put a ding in the surface, but not enough to tear up its innards.

The research was published in the journal Geophysical Research Letters.

What's the difference between an asteroid, meteor and comet? Here's what you need to know, according to Nasa... Asteroid: An asteroid is a small rocky body that orbits the Sun. Most are found in the asteroid belt (between Mars and Jupiter) but they can be found anywhere (including in a path that can impact Earth)

An asteroid is a small rocky body that orbits the Sun. Most are found in the asteroid belt (between Mars and Jupiter) but they can be found anywhere (including in a path that can impact Earth) Meteoroid: When two asteroids hit each other, the small chunks that break off are called meteoroids

When two asteroids hit each other, the small chunks that break off are called meteoroids Meteor: If a meteoroid enters the Earth's atmosphere, it begins to vapourise and then becomes a meteor. On Earth, it'll look like a streak of light in the sky, because the rock is burning up

If a meteoroid enters the Earth's atmosphere, it begins to vapourise and then becomes a meteor. On Earth, it'll look like a streak of light in the sky, because the rock is burning up Meteorite: If a meteoroid doesn't vapourise completely and survives the trip through Earth's atmosphere, it can land on the Earth. At that point, it becomes a meteorite

If a meteoroid doesn't vapourise completely and survives the trip through Earth's atmosphere, it can land on the Earth. At that point, it becomes a meteorite Comet: Like asteroids, a comet orbits the Sun. However rather than being made mostly of rock, a comet contains lots of ice and gas, which can result in amazing tails forming behind them (thanks to the ice and dust vapourising)

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In other news, it emerged this week that alien technology and fossils from a billion years ago could be lurking on the Moon.

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