(ORDO NEWS) — In 2018, NASA astronomers discovered the first evidence of water ice on the Moon. Lurking at the bottom of pitch-black craters at the moon‘s north and south poles, the ice was locked in perpetual shadow and appears to have survived untouched by the sun’s rays, perhaps for millions of years.
However, the discovery of water ice came with a new mystery. While these polar craters are shielded from direct sunlight, they are not shielded from the solar wind, waves of charged particles that blast out of the sun at hundreds of miles per second.
This ionized wind is highly erosive and should have broken ice on the moon long ago, Paul Lucy, a planetary scientist at the University of Hawaii, told Science in an interview. And unlike the Earth, the Moon no longer has a magnetic shield to protect it from being hit by these charged particles.
How, then, was the polar ice on the moon preserved? A new map of the moon’s south pole and the strange pockets of the magnetic field that are there may provide an answer to this question.
In a study presented at the Lunar and Planetary Science Conference last month, scientists from the University of Arizona shared their map of magnetic anomalies – regions of the lunar surface that contain unusually strong magnetic fields – scattered across the moon’s south pole.
These anomalies, first discovered during the Apollo 15 and 16 missions in the 1970s, are the remnants of the Moon’s ancient magnetic shield that probably disappeared billions of years ago, according to NASA.
The magnetic anomalies intersect with several large polar craters that are in permanent shadow and may contain ancient ice deposits. According to the researchers, these anomalies could serve as tiny magnetic shields that protect lunar water ice from constant bombardment by the solar wind.
“These anomalies can deflect the solar wind,” Lon Hood, a planetary scientist at the University of Arizona, told Science. “We think they can be quite significant for protecting permanently shaded areas.”
In their study, the authors combined 12 regional maps of the lunar south pole, originally compiled by the Japanese Kaguya spacecraft, which orbited the moon from 2007 to 2009. Among the scientific instruments of the apparatus was a magnetometer capable of detecting pockets of magnetism on the lunar surface.
With a composite map in hand, the researchers saw that the magnetic anomalies coincided with at least two permanently shadowed craters – Shoemaker and Sverdrup – at the south pole of the moon.
Although the strength of these anomalies is only a small fraction of the strength of Earth’s magnetic field, they can still “significantly deflect ion bombardment” from the solar wind, the researchers said in their presentation. This could be the key to the longevity of water ice on the Moon.
No one knows exactly where the magnetic anomalies on the moon came from. According to one theory, they originated about 4 billion years ago, when the moon still had its own magnetic field, according to a 2014 article written by Hood in the Encyclopedia of Lunar Science.
When large, iron-rich asteroids crashed into the moon during this epoch, they could create magmatic surfaces that slowly cooled over hundreds of thousands of years, becoming permanently magnetized by the moon’s magnetic field.
Upcoming lunar missions may shed light on the dark deposits of ice at the moon’s south pole. The Artemis mission, which will eventually return a man to the lunar surface for the first time since 1972, plans to land astronauts at the moon’s south pole and establish a permanent base there. Studying the ice deposits in this region can reveal how they were created and why they lasted so long.
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