Will Lunar Vertex solve the mystery of lunar vortices?

Impactful ideas

But where to do where do lunar vortices come from? Blewett says there are three main hypotheses to explain the formation of lunar vortices.

The first two ideas postulate an external amplification of magnetic fields during impacts on the Moon, either from the gas and dust of a comet’s coma, or from the cloud of vapor and plasma generated by a large impact crater. about the size of a basin. Such large impacts project matter, called ejecta, which, in the Moon’s low gravity, can travel vast distances and converge towards the antipodal point of impact on the opposite side of the Moon. During its journey, the material is magnetized by “complicated means,” Blewett explains.

Peter Schultz and Leonard Srnka proposed in a 1980 Nature paper that a comet with a diameter of between 650 and 1,640 feet (200 to 500 meters) – and possibly two core fragments – struck the moon, creating Reiner Gamma. They even found candidate impact sites for their proposed double impactor: Goddard A and the O ‘Day crater rim. Goddard and his satellite craters are on the eastern limb of the Moon at Mare Marginis, while O’Day is on the far side. But if comets are responsible for this and other eddies, why aren’t there more of them? After all, as lunar researcher and author Charles Wood writes, “Various studies have shown that impacts from comets are expected to be just as common as those from asteroids. Additionally, one study failed to show spectral evidence at Reiner Gamma of materials typically associated with comets.

But if vortices are associated with the ejection of impacts of antipodal impacts, why is Reiner Gamma not antipode to such an impact? A suggestion from Lon Hood of the University of Arizona’s Lunar and Planetary Laboratory and others is that Reiner Gamma may have formed from ejecta from Cavalerius Crater. But it could also be a consequence of the enormous impact of Mare Imbrium almost 4 billion years ago, an idea Hood supports. As it turns out, the Apollo impact breccias are the most magnetic lunar specimens, showing that impacts can induce magnetism.

Referencing a 2019 article he co-wrote in Journal of Geophysical Research: PlanetsHood suspects that most of the lunar magnetic anomalies were caused by iron-rich ejecta produced by the impactor that created the basin. For example, “the Imbrium Basin is the youngest large basin on the near face of the Moon and many magnetic anomalies (including Reiner Gamma) are aligned radially with respect to this basin,” he says. So instead of invoking an antipodal impact, his claim is that the ejecta – now buried – deposited by the Imbrium explosion are the cause of Reiner Gamma’s mysterious white markings.

Hood also says that “Imbrium’s iron-enriched ejecta converged on the far side of the Moon at the antipode to produce the largest cluster of strong anomalies on the Moon. Similar concentrations of anomalies are found across from several other young lunar basins. The pieces of ejecta would have been so large that they would have cooled slowly, “while they were magnetized,” Hood adds. And any pre-existing magnetic field inside the Moon would have magnetized the ejecta more.

Hood says that Reiner Gamma “is perhaps the most enigmatic feature of the Moon and its origin is unlikely to be fully resolved for a long time.” That’s because, he says, the feature has two separate issues: the origin of its magnetic anomaly and the origin of its light-colored curvilinear albedo marks. “The albedo marks are probably a secondary consequence of the magnetic anomaly,” Hood adds, “but exactly how… is an ongoing mystery.”

But the Lunar Vertex mission will certainly help solve that conundrum, he says.

Interior work

But there is a third possibility for the Reiner Gamma magnetic field – and others like it – that involves no impact. This idea is an endogenous, or internal, possibility that lava cooled on or near the surface at a time when the Moon had its own global magnetic field. As the molten rock solidified, it retained a record of the field even as the lunar interior cooled and the dynamo that generated the field died.

Douglas J. Hemingway and Sonia M. Tikoo suggested in 2018 that “heating associated with magmatic activity” within the Moon may have increased localized magnetic fields. “We suggest,” they wrote, “that these rocks were probably injected into the crust in the form of dikes and underground channels of flowing lava and that they cooled slowly, causing their content to increase. metal and allowing rocks to capture stable stability recording of the Moon’s ancient global magnetic field.

If the magnetic anomalies are endogenous, it raises questions about the volcanic and geochemical processes that produced rocks rich in metallic iron, suggests Blewett. Moreover, nothing in the Apollo, Luna or Chang’e sample collections has such compositions.

Whatever the cause, it appears that localized magnetic fields protect the surface from normal spatial alteration that darkens the regolith in non-magnetic areas. It is also possible that local electromagnetic effects cause high albedo, or reflectance, of the vortex by causing the movement of electrostatically charged dust over the vortices.

How strong are these fields? Blewett says: “We don’t really know the strength of the local field field on the ground in any of the magnetic anomalies. This will be one of Lunar Vertex’s major contributions! However, he adds, the fields are unlikely to be strong enough to protect the surface (or people or equipment) from dangerous high-energy radiation like cosmic rays or solar energetic particles.

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