Precious metals could exist under the surface of the moon, scientists say.
A team of researchers made the prediction after modelling the geological conditions which could exist on the inside of the Earth’s satellite.
They found that the moon’s mantle is likely rich in certain ‘siderophile’ elements, which are those that, like gold and platinum, bond easily with iron.
It is unclear exactly what precious metals might lie under the moon’s surface, however, and whether such would be easy to extract if desired.
Nevertheless, the results help shine light on why rocks brought back from the moon by the Apollo missions contained less siderophile elements than predicted.
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Precious metals could exist under the surface of the moon, pictured in this artist’s model, suggest experts who modelled the conditions magma experiences inside the natural satellite
Geologist James Brenan of Canada’s Dalhousie University and colleagues set out to work out the composition of the moon’s mantle, specifically that of so-called iron-loving — or siderophile — elements, which include gold and platinum.
Experts believe that these were not part of the moon when it was first formed after a Mars-sized planet collided into the Earth, chucking material up into space.
Instead, they were delivered to the moon in an assortment of impacts around the time that the solar system’s period of formation was coming to an end.
Knowing the proportion of siderophile elements that make up the moon would help researchers determine the extend of the bombardment suffered by the early moon.
The researchers began by considering the material brought back from moon around 50 years ago which is available for us to study directly.
‘We have a grand total of 400 kilograms of sample that was brought back by the Apollo and lunar missions,’ Professor Brenan told ScienceAlert.
‘It’s a pretty small amount of material. So, in order to find out anything about the interior of the Moon we have to kind of reverse engineer the composition of the lavas that come onto the surface.’
Previous research on rocks brought back by the Apollo 15 and 17 missions, however, yielded siderophile levels that were around 10–100 times smaller than expected.
The numbers wouldn’t even add up when experts tried to account for how impacts into the early lunar surface — unlike those hitting the Earth — might have eroded the moon, taking from its overall mass rather than adding to it.
Instead, Professor Brenan and colleagues went back to basics, modelling how rocks on the moon’s surface would have formed from the magma beneath.
They found that the moon’s mantle is likely rich in certain ‘siderophile’ elements, which are those that, like gold and platinum bond easily with iron
They combined models of the pressures and temperatures found in cooling magma with lab-based experiments into how sulphur dissolves in molten rock.
The team found that the parts of the moon’s mantle from which lava comes are dominated by sulphur-poor, iron-rich sulphides that concentrate certain highly siderophile elements more than others — keeping them from reaching the surface.
‘Our results show that sulphur in lunar volcanic rocks is a fingerprint for the presence of iron sulphide in the rocky interior of the moon,’ Professor Brenan told ScienceAlert.
This, he added, ‘is where we think the precious metals were left behind when the lava were created.’
The researchers explain the differences between their models and the measurements of rocks from the moon’s surface as being a product of mixing between the magma and surface rocks that contained impact debris.
‘The composition of the lunar mantle is veiled by regolith contamination of the lunar basalts,’ the researchers wrote in their paper.
‘Highly-siderophile element abundances in lunar mantle-derived materials cannot be used to determine the mass of material accreted late onto the moon.’
This finding also means that we cannot use volcanic rocks from the moon’s surface to indicate which precious metals might be found beneath.
Furthermore, these metals will likely not be found in high concentrations of ore that are easy to mine and process, so a lunar ‘gold rush’ might not be on the horizon.
While the findings of the present study leave much uncertain, scientists may be able to learn more about the moon’s inner composition by studying deep rock formations that have been exposed by impacts in the moon’s southern regions.
‘It’s pretty exciting to think that we might return to the Moon,’ Brenan told ScienceAlert.
‘And if so, the South Pole seems like a good choice for sampling.’
The full findings of the study were published in the journal Nature Geoscience.
WHAT ARE THE THEORIES ON THE ORIGIN OF THE MOON?
Many researchers believe the moon formed after Earth was hit by a planet the size of Mars billions of years ago.
This is called the giant impact hypothesis.
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.
The colliding body is sometimes called Theia, after the mythical Greek Titan who was the mother of Selene, the goddess of the moon.
Many researchers believe the moon formed after Earth was hit by a planet the size of Mars billions of years ago. This is called the giant impact hypothesis
But one mystery has persisted, revealed by rocks the Apollo astronauts brought back from the moon: Why are the moon and Earth so similar in their composition?
Several different theories have emerged over the years to explain the similar fingerprints of Earth and the moon.
Perhaps the impact created a huge cloud of debris that mixed thoroughly with the Earth and then later condensed to form the moon.
Or Theia could have, coincidentally, been chemically similar to young Earth.
A third possibility is that the moon formed from Earthen materials, rather than from Theia, although this would have been a very unusual type of impact.
