Unlike Earth, the moon has no global magnetic field, but patches of the satellite’s surface are magnetic. What gives?
According to new models, these unusually magnetic pockets come from an asteroid that slammed into the moon when it had a magnetic field, billions of years ago, according to Mark Wieczorek, director of research at the Institute of Earth Physics of Paris.
In general, heating metal in a rock and then cooling it imparts magnetic properties—the most common way Earth rocks get magnetized.
“Many of the meteorites we see on the Earth contain large abundances of metallic iron. They’re roughly a hundred times more magnetic than typical rocks you can see on the moon,” said Wieczorek, who co-authored a new study on the phenomenon.
On the moon, “if we can get enough of these asteroid materials”—heated by impact—”in a certain region, that would create a magnetic anomaly that would be a hundred times stronger” than the rest of the moon.
Moon Models Show Asteroid Impact
Wieczorek and his team also found that most of the magnetic material is on the northern rim of the South Pole-Aitken basin, the biggest crater on the moon and among the biggest in the solar system.
In the new models “you start out with a 200-kilometer [124-mile] sphere and smash it into the moon—on a computer, of course—at high velocities. Depending on the impact velocity and angle, we can get large quantities of material deposited on the rim of this impact basin.”
An asteroid that size moving at 9.3 miles (15 kilometers) a second and hitting the moon at a 45-degree angle would spew out moon chunks along a 745-mile-wide (1,200-kilometer-wide) crater, the results showed.
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