AN enormous metal structure buried deep beneath the surface of the Moon has been discovered by scientists.

The mystery blob is larger than Denmark and stretches 180 miles below the Moon's icy south pole.

3 A huge lump of metal has been found deep under the Moon's surface. Pictured inset is false-colour image of the Moon's south pole showing the newly found metal lump within the dotted line. The warmer colours show high topography and the bluer colours indicate low topography

Experts reckon it's shrapnel left behind by a huge collision with an asteroid around 4billion years ago.

The team from Baylor University in Texas, USA, found the metal lump by combining data from two Nasa satellites.

They say it covers roughly 20,000 square miles, making it larger than Denmark (17,000 square miles).

"Imagine taking a pile of metal five times larger than the Big Island of Hawaii and burying it underground," said lead scientist Dr Peter James.

3 Nasa has picked out the Moon's lumpy south pole (pictured) as a potential spot for future lunar bases Credit: Nasa

"That's roughly how much unexpected mass we detected."

Experts combined readings from Nasa's Gravity Recovery and Interior Laboratory (GRAIL) and Lunar Reconnaissance Orbiter missions.

They looked at the largest, oldest, and deepest crater on the Moon: The South Pole-Aitken (SPA) basin.

Spanning 1,240 miles across the Moon's far side, the basin is unusually lumpy, and scientists have long believed it was created by an explosive asteroid impact.

Readings show the rocky world's gravitational pull rises around the SPA basin, suggesting something extremely dense lays beneath.

The team reckons a huge lump of metal is most likely responsible, left behind by the asteroid that created the crater.

3 Scientists think the metal was left behind by an asteroid impact (stock image) Credit: Photographers Choice - Getty

Simulations suggest the space rock had a hot core of molten iron and nickel that was injected into the moon during impact.

"When we combined that with lunar topography data from the Lunar Reconnaissance Orbiter, we discovered the unexpectedly large amount of mass hundreds of miles underneath the South Pole-Aitken basin," Dr James said.

"One of the explanations of this extra mass is that the metal from the asteroid that formed this crater is still embedded in the Moon's mantle."

Another possibility is that the mass might be a concentration of dense chemicals linked to the formation of the Moon, in which its magma ocean solidified into rocks.

The Moon – our closest neighbour explained Here's what you need to know... The Moon is a natural satellite – a space-faring body that orbits a planet

It's Earth's only natural satellite, and is the fifth biggest in the Solar System

The Moon measures 2,158 miles across, roughly 0.27 times the diameter of Earth

Temperatures on the Moon range from minus 173 degrees Celcius to 260 degrees Celcius

Experts assumed the Moon was another planet, until Nicolaus Copernicus outlined his theory about our Solar System in 1543

It was eventually assigned to a "class" after Galileo discovered four moons orbiting Jupiter in 1610

The Moon is believed to have formed around 4.51billion years ago

The strength of its gravitational field is about a sixth of Earth's gravity

Earth and the Moon have "synchronous rotation", which means we always see the same side of the Moon – hence the phrase "dark side of the Moon"

The Moon's surface is actually dark, but appears bright in the sky due to its reflective ground

During a solar eclipse, the Moon covers the Sun almost completely. Both objects appear a similar size in the sky because the Sun is both 400 times larger and farther

The first spacecraft to reach the Moon was in 1959, as part of the Soviet Union's Lunar program

The first manned orbital mission was Nasa's Apollo 8 in 1968

And the first manned lunar landing was in 1969, as part of the Apollo 11 mission

The huge mass—"whatever it is, wherever it came from"—is weighing the basin floor downward by more than half a mile, Dr James added.

It could prove lucrative if humans ever land at the Moon's South Pole.

Nasa has previously picked out the spot as a potential site for a lunar base, as lots of water ice is stored there.

The agency says mining the Moon for resources will be key to any humans living there long term.

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What do you think the lump is? Let us know in the comments!

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