Just like the people on Earth, the moon could also do with a bit of sunscreen to protect its surface from the sun’s scorching rays. This is because every object in the solar system, including Earth and its natural satellite, is exposed to what scientists call the solar wind — a continuous outflow of charged particles coming from the sun, which floods the entire solar system, washing over all the planets and the smaller celestial bodies inhabiting the system.
As a result, every object floating in the solar system has to deal with the sun’s piercing rays. Earth manages to do so thanks to its magnetic field — a protective grid of electric currents that encompasses the entire planet, shielding it from solar wind and harmful cosmic radiation.
Unlike Earth, the moon doesn’t have a global magnetic field. Instead, it relies on magnetic rocks near its surface, which only provide small, localized bubbles of protection. This allows the charged solar particles to breach the protective barrier and blast the lunar surface with a lot more radiation. And, as expected, it shows on the moon’s “skin.”
“Every object, planet or person traveling through space has to contend with the sun’s damaging radiation,” notes NASA, “and the Moon has the scars to prove it.”
The lunar surface boasts a “distinctive pattern of darker and lighter swirls,” some of them large enough to be visible from Earth. One such example is the 37-mile-wide Reiner Gamma lunar swirl, imaged below by NASA’s Lunar Reconnaissance Orbiter.
According to new data from the space agency’s ARTEMIS mission, some of the colorations we see on the moon could actually be a form of “sunburn.” Short for Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun, ARTEMIS suggests that the swirl pattern may be created by the solar wind as it interacts with the magnetic fields on the moon’s crust.
“The magnetic fields in some regions are locally acting as this magnetic sunscreen,” explains Andrew Poppe, a scientist at the University of California, Berkeley, who studies the moon’s magnetic environment using data from the ARTEMIS mission.
These tiny spots of magnetic “sunscreen” act like small umbrellas that deflect solar wind particles, keeping the patches of the lunar surface underneath safe from radiation. As a result, the lunar regolith – dust and surface material – found under the protective umbrellas dons a bright coloration, leading to the formations of the white lunar swirls found in hundreds of places across the moon’s surface.
Meanwhile, the surrounding areas where the solar particles get deflected gradually become darker under the influence of chemical reactions. This suggests that the white swirls visible on the lunar surface signal the areas where the small bubbles of magnetic “sunscreen” are in effect.
“Sometimes you put on sunscreen and you miss, like, a tiny little bit. And then you have a really bright red spot on your skin where you missed it. That’s in some ways the analogy of this region of the moon that is extra-exposed,” Poppe details in the video below.
The new findings are consistent with the previous data on the mysterious lunar swirls. In 2016, NASA reported that these features were found to appear in locations on the lunar crust with embedded bits of magnetic field. In addition, past research showed that the bright areas in the swirls were “less weathered than their surroundings.”
While the small bubbles of magnetic field where the lunar swirls occur are not robust enough to shield astronauts from radiation, studying the moon’s magnetic environment may lead to the development of new techniques to keep future moon explorers safe.