The moon is covered in tattoo-like swirls of light and dark material, and scientists may finally know why.
"These patterns, called 'lunar swirls,' appear almost painted on the surface of the moon," John Keller, a NASA scientist, said in a statement. "They are unique; we've only seen these features on the moon, and their origin has remained a mystery since their discovery."
Here's what they look like:
There are over 100 of them, and some span tens of miles wide, according to NASA.
Scientists aren't sure where they come from, but they've come up with a few theories over the years. The swirls often appear where remnants of the moon's magnetic field lingers in the crust, so one theory is that the magnetized lunar surface causes them.
High-speed streams of charged particles called solar wind low off the sun, hit the moon's surface and darken it. But scientists think the magnetized crust might interact with the solar wind and shield some of the surface from the charged particles. So that's why swirls of brighter material are sprinkled across the moon.
The theory isn't perfect, though. "The problem with the magnetic shield idea is that the embedded magnetic fields on the moon are very weak — about 300 times weaker than Earth's magnetic field," Bill Farrell, a NASA scientist, said in a statement. "It's hard to see how they would have the strength to deflect the solar wind ions."
But new models reveal that the magnetic fields might also create powerful electric fields that are strong enough to protect the surface from solar winds.
"It is this brawny electric potential of many hundreds of volts that could deflect and slow particles in the solar wind," NASA explains. "This would reduce the weathering from the solar wind, leaving brighter regions over protected areas."
It's a good explanation, but it isn't definitive. We won't be able to confirm what's causing the swirls until we have astronauts walking on the moon again taking measurements.