In 2018 scientists documented the first evidence of water ice on the Moon that was trapped in the bottom of craters at the north and south poles locked in perpetual shadow. Discovery of the ice created new questions. While the craters are protected from direct sunlight, they aren’t shielded from solar wind. The ionized particles from the Sun is highly erosive and, unlike the Earth, the Moon has no magnetic shield to protect it. By some peoples’ reckoning, the solar wind should have destroyed the ice long ago.
In research presented at the Lunar and Planetary Science Conference last month, University of Arizona scientists shared their map of magnetic anomalies, regions of the lunar surface with unusually strong magnetic fields, reports LiveScience.
These anomalies may serve as tiny magnetic shields.”These anomalies can deflect the solar wind,” Lon Hood, a planetary scientist at the University of Arizona, told Science. “We think they could be quite significant in shielding the permanently shadowed regions.”
Magnetic anomalies overlap with the permanently shadowed Shoemaker and Sverdrup craters at the lunar south pole. Though only a fraction of the strength of Earth’s magnetic field, the fields still could “significantly deflect the ion bombardment” of solar wind, the researchers said in their presentation.
No one is sure where the anomalies come from. One theory is that they resulted from large, iron-rich asteroids crashing onto the surface back when the Moon did have a magnetic field some 4 billion years ago, creating magma surfaces that cooled over hundreds of thousands of years, magnetizing in the process.
Hood would like collect data that would shed more light by putting a solar-wind instrument on the surface to measure the charged particles that pass the rim of the crater. “You would also need to collect samples and identify what is magnetized,” he said.