Our solar system is passing through one of the spiral arms that makes the Milky Way Galaxy look like a pinwheel. But the key words there are “passing through.” The solar system moves through the galaxy a little faster than the spiral arms do. So over hundreds of millions of years, we cross all of the galaxy’s major arms. And those crossings could be dangerous.

A spiral arm is a region where a passing wave squeezes giant clouds of gas and dust, triggering the birth of new stars. Many of the stars are especially hot and bright, so they light up the spiral arms.

The star-forming clouds are dense and turbulent. And a recent study suggested that could be where the “danger” comes in.

Researchers looked at tiny crystals in Earth’s crust. They found that the composition of the crystals varied over periods of hundreds of millions of years.

During some of those periods, Earth’s crust appeared to be especially hot. And the timing of those periods may correspond to passages through the spiral arms.

As we move through the dense clouds in the arms, big balls of ice and rock far from the Sun could be nudged inward. Some of them could ram into Earth, creating conditions that could account for some of the crystals. So while the Milky Way’s spiral arms may be beautiful, they may also be deadly.

Look for the glowing band of the Milky Way curving across the east as night falls, and arching high overhead later on.

Script by Damond Benningfield