The Moon might be more metallic than researchers thought. And that comes from no less a source than NASA.
The scientists who operate the Miniature Radio Frequency (Mini-RF) instrument on the Lunar Reconnaissance Orbiter spacecraft have found evidence about the distribution of iron and titanium oxides in the lunar subsurface which, they say, could aid in drawing a clearer connection between Earth and the Moon.
Their findings are published in a paper in Earth and Planetary Science Letters.
Evidence points to the Moon as the product of a collision between a Mars-sized protoplanet and young Earth, and the Moon’s bulk chemical composition closely resembles that of Earth’s. There are discrepancies, however, and scientists have speculated about what contribution the protoplanet might have made.
The Mini-RF team says it has found a curious pattern that could lead to an answer.
The researchers sought to measure an electrical property within lunar soil piled on crater floors in the Moon’s northern hemisphere. It is known as the dielectric constant, a number that compares the relative abilities of a material and the vacuum of space to transmit electric fields and could help locate ice lurking in the crater shadows.
The team noticed this property changed with crater size. For craters two to five kilometres in width, the dielectric constant of the material steadily increased as the craters grew larger, but for craters of between five and 20 kilometres it remained constant.
“It was a surprising relationship that we had no reason to believe would exist,” says Essam Heggy, the paper’s lead author and co-investigator of the Mini-RF experiments.
Because meteors that form larger craters also dig deeper into the Moon’s subsurface, the team reasoned that the increasing dielectric constant of the dust in larger craters could be the result of meteors excavating iron and titanium oxides that lie below the surface. Dielectric properties are directly linked to the concentration of these metal minerals.
If their hypothesis were true, it would mean only the first few hundred metres of the Moon’s surface is scant in iron and titanium oxides, but below the surface, there’s a steady increase. Comparing Mini-RF radar images from with metal oxide maps confirmed this, they say.
The larger craters, with their increased dielectric material, were also richer in metals, suggesting that more iron and titanium oxides had been excavated from the depths of 0.5 to two kilometres than from the upper 0.2 to 0.5 kilometres.
The researchers stress that the new study can’t directly answer the outstanding questions about the Moon’s formation but, says Heggy, “it really raises the question of what this means for our previous formation hypotheses”.
They have begun examining crater floors in the Moon’s southern hemisphere to see if the same trends exist there.
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