Research suggests that the solar wind and the Moon’s crustal magnetic fields work together to give the Moon a distinctive pattern of darker and lighter swirls — patterns that are so prominent they can be seen from Earth.

Here’s how it happens: Magnetized rocks near the lunar surface create small, localized spots of magnetic field that extend anywhere from hundreds of yards to hundreds of miles. As solar wind particles flow toward the Moon, they are deflected to the areas just around the magnetic bubbles, where chemical reactions with regolith — the material that makes up the Moon’s surface — darken the surface. Under these miniature magnetic umbrellas, the regolith is shielded from the Sun’s particles, creating the swirls of darker and lighter material.

The complete NASA Story