Mystery of swirls on Moon may finally have an answer — they're formed by solar wind

Swirls on the moon seem to be a kind of sunburn from how solar wind & the crust magnetic field interact.

Whether you're a spaceship, plant or banana flying through space, one thing that you will have to prepare for is Sun damage. Out in space, the Sun's radiation spikes during events called 'solar flares' — and the Moon has the scars to prove it.

NASA's ARTEMIS mission is short for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun. The mission is centred around a pair of satellites that are currently orbiting the Moon — looking into the Earth-Moon Lagrange points, solar wind, and how the Earth and Moon's magnetic fields interact with solar wind.

Solar wind is a continuous stream of charged particles that come from the Sun, flood the entire solar system, and wash over all planets and celestial bodies that exist in the solar system.

Every object in the solar system has to withstand the Sun’s piercing rays. In the case of Earth, its magnetic field shields all things on the planet's surface from solar wind and harsh radiation in space.

However, the strength of Earth's magnetic field isn't strong enough to extend this protection to the Moon. Much of the Moon's surface is exposed to solar wind particles that blast its surface. New data collected by the ARTEMIS mission suggest that a combination of solar wind and the Moon's magnetic field leave behind distinctive patterns of darker and lighter swirls, some of which are visible to us on the Moon's surface.

One such example is the lunar swirl called Reiner Gamma, one of the most prominent on the Moon. It was captured in a stunning image by NASA’s Lunar Reconnaissance Orbiter last year.

Mystery of swirls on Moon may finally have an answer — theyre formed by solar wind

Research using data from NASA's ARTEMIS mission suggests that lunar swirls, like the Reiner Gamma lunar swirl imaged here by NASA's Lunar Reconnaissance Orbiter, could be the result of solar wind interactions with the Moon's isolated pockets of the magnetic field. Image courtesy: NASA/Lunar Reconnaissance Orbiter

Reiner Gamma and the dozens of other swirls on the Moon could simply be a form of "sunburn" created by how solar wind and the magnetic field of the Moon's crust interact.

The surface is exposed to any and all radiation coming its way from space, and the only protection it has is from small magnetic rocks in the moon's crust and surface. These provide the lunar surface with small and localised pockets of protection from solar wind.

When solar wind collides with Earth's magnetic field. Image courtesy: NOAA/National Geophysical Data Cantre

When solar wind collides with Earth's magnetic field. Image courtesy: National Geophysical Data Cantre

"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," Andrew Poppe, a scientist at the University of California, Berkeley that studies the Moon’s magnetic environment using data from the ARTEMIS mission.

This finding matches earlier ones about lunar swirls. For instance, NASA reported in 2016 that the swirls came up in regions of the Moon's crust that had a magnetic field. Bright areas in the swirls were also found to be "less weathered than their surroundings."

While these swirls are certainly too small to protect astronauts that go to the Moon, they could point to new techniques to keep future astronauts or lunar settlers safe from the perils of space radiation.

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