Titanium Moon: A Theory Explains Variable Lunar Magnetism

The rocks returned to Earth during NASA's Apollo program from 1968 to 1972 provided volumes of information on the history of the Moon, but they were also the source of an unexplained scientific mystery. Analysis of the rocks revealed that some appeared to have formed in the presence of a strong magnetic field, one that rivaled that of the Earth in strength. But it wasn't clear how a moon-sized body could have generated such a strong magnetic field.

Now, research led by a geoscientist at Brown University proposes a new explanation for the magnetic mystery of the Moon. The study, published in Nature Astronomy , shows how giant titanium-rich rock formations sinking through the lunar mantle may have produced the kind of internal convection that generates strong magnetic fields. The processes may have produced strong intermittent magnetic fields for the first billion years of the Moon's history, exactly as shown by the lunar rocks.

"Everything we have thought about how magnetic fields are generated by planetary nuclei tells us that a body the size of the Moon should not be able to generate a field as strong as Earth's," said Alexander Evans, an assistant professor of Earth. , environmental and planetary sciences at Brown and co-author of the study with Sonia Tikoo of Stanford University. “But instead of thinking about how to power a strong magnetic field continuously for billions of years, perhaps there is a way to get a high intensity field intermittently. Our model shows how this can happen and is consistent with what we know about the interior of the Moon ”.

Planetary bodies produce magnetic fields through what is known as the central dynamo. The slow dissipation of heat causes the convection of molten metals in a planet's core. The constant stirring of electrically conductive material is what produces a magnetic field. This is how the Earth's magnetic field is formed, which protects the surface from the sun's most dangerous radiation.

The Moon lacks a magnetic field today, and models of its core suggest it was probably too small and lacked the convective force to ever produce a relevant magnetic field. For a core to have strong convective rotation, it must dissipate a lot of heat. In the case of the first Moon, Evans says, the mantle surrounding the core was not much colder than the core itself. In the absence of a hot core and a cold mantle, as occurs in the Earth, no convective currents are created that feed the magnetism. But this new study shows how sinking rocks could have provided intermittent convection thrusts.

The story of these sinking stones begins a few million years after the formation of the Moon. Very early in its history, the Moon is thought to have been covered with an ocean of molten rock. As the vast ocean of magma began to cool and solidify, minerals such as olivine and pyroxene that were denser than liquid magma sank to the bottom, while less dense minerals such as anorthosite floated to form the crust. The remaining liquid magma was rich in titanium and heat-producing elements such as thorium, uranium and potassium, so it took a little longer to solidify. When this titanium layer finally crystallized just below the crust, it was denser than the minerals that had previously solidified under it. Over time, the titanium formations sank through the less dense rock of the mantle below, a process known as gravitational flip.

For this new study, Evans and Tikoo modeled the dynamics of how those titanium formations would sink, as well as the effect they might have when they reached the Moon's core. The analysis, based on the current composition of the Moon and the estimated viscosity of the mantle, showed that the formations would likely have shattered into small plates up to 60 kilometers in diameter and sank intermittently over the course of about a billion years. .

When each of these fragments touched the bottom, that is, the core, they would have given a great shock to the central dynamo of the Moon. Being located just below the lunar crust, the titanium formations would have had a relatively cool temperature, much cooler than the estimated core temperature of about 2,600 and 3,800 degrees Fahrenheit. When the cold blobs made contact with the hot core after sinking, the temperature discrepancy would have caused the core's convection to increase, enough to drive a magnetic field on the Moon's surface that is stronger or even stronger than Earth's.

“You can think of it a bit like a drop of water hitting a hot pan,” Evans said. “You have something really cold touching the core, then suddenly a heat loss starts. This causes an increase in activity in the core, which gives you these intermittently intense magnetic fields. "

There could have been up to 100 of these descending events in the first billion years of the Moon's existence, the researchers say, and each could have produced a strong magnetic field lasting about a century. The sum of these short periods would have generated a relatively long period of irregular and intermittent lunar magnetism, exactly as found in lunar rocks.

So there is a lot of titanium in the lunar core. With the price of the metal it is strange that someone has not already thought about going to collect it.

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The article Luna di Titanio: a theory explains the variable lunar magnetism comes from ScenariEconomici.it .

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This is a machine translation of a post published on Scenari Economici at the URL https://scenarieconomici.it/luna-di-titanio-una-teoria-spiega-il-variabile-magnetismo-lunare/ on Fri, 28 Jan 2022 13:00:17 +0000.