Do you ever know the Moon's half-century magnetic mystery?
It wasn’t clear how a Moon-sized body could have generated a magnetic flux that strong. But now, the study, published in ‘Nature Astronomy’, has shown that big rock formations sinking through the Moon’s mantle could have produced the type of interior convection that generates strong magnetic fields. Ever since rocks were brought back from the Moon to the world, during NASA’s Apollo program from 1968 to 1972, an everlasting mystery continued to baffle scientists: the Moon’s magnetic flux – one that rivaled Earth’s in strength. Now, research led by a Brown University geoscientist proposes a replacement explanation for the Moon’s magnetic mystery.
It wasn’t clear how a Moon-sized body could have generated a magnetic flux that strong. But now, the study, published in ‘Nature Astronomy’, has shown that big rock formations sinking through the Moon’s mantle could have produced the type of interior convection that generates strong magnetic fields.
The processes could have produced intermittently strong magnetic fields for the primary billion years of the Moon’s history, the researchers said. “Everything that we’ve considered how magnetic fields are generated by planetary cores tells us that a body of the Moon’s size shouldn't be ready to generate a field that’s as strong as Earth’s,” said Alexander Evans, a professor of Earth, environmental and planetary sciences at Brown and co-author of the study with Sonia from Stanford University.
“But rather than brooding about the way to power a robust magnetic flux continuously over billions of years, maybe there’s how to urge a high-intensity field intermittently. Our model shows how, which will happen, and it’s according to what we all know about the Moon’s interior.” Planetary bodies are known to supply magnetic fields through what’s referred to as a core dynamo.
The Moon lacked a magnetic flux, and models of its core suggested that it had been probably too small and lacked the convective force to possess ever produced a continuously strong magnetic flux. So as for a core to possess a robust convective churn, it needed to dissipate tons of warmth. Within the case of the first Moon, Evans said, the mantle surrounding the core wasn’t much cooler than the core itself. Because the core’s heat didn’t have anywhere to travel, there wasn’t much convection within the core.
The story of those sinking stones started a couple of million years after the Moon’s formation. Very early in its history, the Moon is assumed to possess been covered by an ocean of molten rock. Because the vast magma ocean began to chill and solidify, minerals like olivine and propene that were denser than the liquid magma sank to the rock bottom, while less dense minerals like anorthosites floated to make the crust.
The remaining liquid magma was rich in titanium also as heat-producing elements like thorium, uranium, and potassium, so it took a touch longer to solidify. When this titanium layer finally crystallized just beneath the crust, it had been denser than the earlier-solidifying minerals below it. Over time, the titanium formations sank through the less-dense mantle rock underneath, a process referred to as gravitational overturn.
For this new study, Evans modeled the dynamics of how those titanium formations would have sunk, also because of the effect they could have once they eventually reached the Moon's core. The analysis, which was supported in the Moon's current composition and therefore the estimated mantle viscosity, showed that the formations would likely force an entry blob as small as 60 kilometers and diameter, and sink intermittently over a few billion years.
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