Despite its appearance, the Moon is dark. On average, its surface reflects only about a tenth of the sunlight that strikes it. But some regions are much brighter than their surroundings. They contain loops and squiggles that can stretch for dozens of miles. Some are big enough to see through small telescopes. And planetary scientists are still trying to figure out what causes them.

These features are known as lunar swirls. Many of them look like ribbons of cream poured into a cup of hot coffee. The most famous, Reiner Gamma, looks like a tadpole. It has an oval “head,” with a wiggly tail that extends far across the dark plains around it.

All of the swirls have especially strong magnetic fields. The Moon itself doesn’t generate a magnetic field. But pockets of magnetic force might have been “frozen” in place in the rocks.

The magnetic field forms a protective dome. It deflects the solar wind – a flow of charged particles from the Sun. The particles are diverted away from the swirl. They may darken the surrounding area, but leave the swirl fairly bright.

The magnetic pockets could be created by impacts by iron-rich meteorites, below-ground flows of molten rock, or some other process. NASA plans to land a rover in Reiner Gamma as early as next year – perhaps revealing the origins of these bright features on the dark lunar surface.

Look for the Moon in the wee hours of tomorrow morning. The bright star Spica stands close by.

Script by Damond Benningfield