Unexplained Magnetic Anomalies on the Moon Are Protecting Its Ice, Scientists Say

Two of the most enduring Moon mysteries may be deeply linked, according to new research.
Two of the most enduring Moon mysteries may be deeply linked, according to new research.
Visualization of the permanently shadowed regions of the Moon. Image: 

NASA's Goddard Space Flight Center

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Unexplained magnetic anomalies on the Moon may be shielding precious deposits of water ice that lie in permanent shadow at the lunar poles, according to new research

The hypothesis could help solve the mystery of the Moon’s polar ice, which was definitively confirmed to exist in 2018, a discovery that has major implications for understanding both the geological history and future exploration of Earth’s only natural satellite, by robots and humans.

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Scientists led by Lon Hood, a research professor at the University of Arizona, have now linked the presence of magnetic hotspots and water ice on the Moon by producing an updated map using data from Japan’s Kaguya satellite, which orbited the Moon from 2007 to 2009. They presented the work at the Lunar and Planetary Science Conference, held last month in Houston, Texas. 

The team demonstrated that local magnetic fields at the poles may be warding off the erosive solar wind, a stream of charged particles, called ions, emitted by the Sun, thereby enabling water ice to persist in these lunar nooks and crannies. 

“Moderate magnetic anomalies are present directly over at least two permanently shadowed craters near the lunar south pole,” Hood and his colleagues reported at the conference. “While these anomalies (and lunar magnetic anomalies in general) are too weak to shield future astronauts from biologically harmful cosmic radiation, they could assist in shielding these craters and any water ice therein from the solar wind ion bombardment.”

The Moon’s odd magnetic hotspots were first discovered by Apollo astronauts toward the tail-end of the lunar landings. Despite this long-standing awareness of the anomalies, their origin continues to evade explanation. 

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Some scientists have suggested that these areas were transformed by iron-rich meteorites—or perhaps one large asteroid—that impacted the Moon more than four billion years ago, producing molten regions that became permanently magnetized after they hardened. They could also be remnants of an overarching magnetic field that once enveloped the Moon, but has since weakened into regional hotspots. 

Likewise, the origin of the Moon’s water ice, which may also date back billions of years, raises as many questions as answers. Though these deposits are located in craters that are shielded from direct sunlight, they should theoretically be within reach of the solar wind. With no atmosphere or global magnetic field to protect the ice from the wind’s corrosive particles, it’s unclear how they have survived, even in eternal shade.   

Hood and his colleagues used Kaguya’s high-resolution data to overlay the topography of the lunar poles with the presence of known magnetic regions. The approach revealed that “relatively strong anomalies are directly over several permanently shadowed craters,” according to the team’s conference presentation. In particular, the researchers noted that the Shoemaker and Sverdrup craters, which are both near the Moon’s south pole, contain shadowed regions that are under these natural magnetic domes.

The new results help to shed light on the Moon’s sunless regions. Hood and his colleagues suggest that future observations and ground missions should target these icy regions for further exploration. 

To that end, NASA is already gearing up to send a rover called VIPER (Volatiles Investigating Polar Exploration Rover) to the south pole by 2023. This mission will investigate whether the Moon’s ice could be harvested as a resource to support more ambitious trips to the Moon, including a human return to the Moon that NASA is planning this decade as part of its Artemis program. 

In this way, a discovery first made by Apollo astronauts may soon be utilized by Artemis astronauts, potentially paving the way for human missions beyond the Moon.