Moon anomaly: ‘MASSIVE’ deposit beneath Moon’s largest crater is ancient asteroid metal

The crater is several kilometres deep but can not be seen from Earth because it is located in the far side of the Moon, which is permanently turned away from Earth for astronomers and telescopes to study.

Earth's moon is hiding an enormous secret on its storied dark side.

The anomaly was discovered when the scientists measured subtle changes in the strength of gravity around the moon, analysing data collected from NASA missions. Ideas for what the mysterious lump may be include the splattered core of a giant metallic asteroid or an ocean of red-hot magma that slowly froze in place.

This mass, the researchers believe, is weighing the floor of the basin downward by more than 800 metres, around 10 percent of its total depth, explaining a depression in the bottom of the basin previously attributed to contraction.

'Imagine taking a pile of metal five times larger than the big Island of Hawaii and burying it underground, ' said lead author Peter B. James, from Baylor University's College of Arts & Sciences.

The research is described in a paper published April 5 in the journal Geophysical Research Letters.

A rendering of a lunar rover for China's Chang'e-4 moon mission. Things like when researchers successfully brought some frozen 40,000-year-old worms back to life last year or when Harvard's astronomy chair theorised that 'Oumuamua, the first interstellar object ever documented passing through our solar system, could be a solar-sail-powered alien probe.

The theory suggests the moon is made up of debris left over following a collision between our planet and a body around 4.5 billion years ago.

If the mass is from around the same time as the impact that made the basin, this implies an upper temperature limit of around 1,480 degrees Celsius for the latter half of the Moon's lifespan, consistent with estimates based on seismology.

Whatever formed the basin almost 4 billion years ago remains a mystery, but the blow was so strong that it likely punched all the way through the moon's crust and tossed part of the lunar mantle - a deeper geologic layer - onto the surface.

This data had already indicated a gravitational anomaly, and that the basin had higher-than-average density compared to the rest of the lunar surface; the team attributed this to its iron-rich surface composition.

A previously unknown deposit of an unidentified physical substance larger than the size of Hawaii has been discovered beneath the surface of the moon.

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

The South Pole-Aitken basin on the far side of the moon is said to be the largest crater in the solar system and extends several miles deep. Instead of sinking down into the moon's interior, it remained buried in the moon's mantle. The researchers think such splattering may have kept the metal floating beneath the crust; otherwise it might have sunk down into the moon's core.

Another source of the unexpected mass, researchers say, could be a concentration of oxides that could have formed when the magma ocean that existed on the moon solidified.