Attack From Outer Space

The explosion in Chelyabinsk was a reminder of something that’s easy to forget: We live on a planet drifting through space. And drifting along with us are billions of rocks—leftovers from when our solar system formed about 4.6 billion years ago. There are meteoroids, which can be as tiny as a speck of dust or as big as a school bus, and their larger cousins, asteroids, some of which stretch more than 300 miles across. And there are comets, mixtures of frozen gases, rock, and dust.

For the most part, space rocks stay in the asteroid belt, between Mars and Jupiter. Occasionally, though, they knock into each other, bouncing around like bumper cars, and come zooming our way.

As these runaway rocks hurtle toward Earth, they move at incredibly high speeds—tens of thousands of miles per hour. They grow so scorchingly hot that most vaporize high in the atmosphere without causing any damage. The rocks that do make it to the ground are called meteorites. They’re mostly tiny and harmless.

What happened over Chelyabinsk was different. That space rock was a whopping 65 feet wide—about the width of a basketball court. As it zoomed through the atmosphere, it grew hotter and hotter until, about 14 miles above the city, it exploded. The force of the blast was so powerful, it was like a bomb detonating.

Mentions of falling rocks appear in many ancient writings. The Greeks and Romans believed that space rocks were sacred messages from the gods. The Egyptians fashioned jewelry from meteorites, which they called “metal of heaven.” In ancient Mongolia, seeing a comet streak across the sky was thought to be a harbinger of doom. It wasn’t until the 1700s that scientists understood the rocks came from space.

Today we know a lot about space rocks, and we know that most are nothing to worry about. A large rock coming close to Earth’s surface—like what happened in Chelyabinsk—doesn’t happen often, only once or twice every 100 years. But what if the rock had been much bigger—say the size of a town? And what if it had crashed to the ground?

That would have been a catastrophe. In fact, such an event is likely what led to the extinction of the dinosaurs some 66 million years ago. Most scientists believe a giant asteroid crashed off the coast of what is now Mexico. Dust clouds from the impact likely blocked out the sun—perhaps for months or even years—causing many plants and animals to die.

The good news is that large asteroid events like the one that doomed the dinosaurs are extremely rare, occurring only every 50 to 100 million years. Still, scientists around the world are working to protect our planet. NASA, America’s space agency, uses telescopes to track large asteroids, and it is building more powerful telescopes that can spot smaller rocks.

As for what we would do if a massive rock were headed straight for us, scientists have many ideas. We could blast it apart with bombs or shoot it with lasers. We could also redirect the rock away from Earth by crashing an unpiloted spacecraft into it. The idea is that what happened in Chelyabinsk could be prevented, or at least there would be enough warning for people to evacuate before an explosion or crash.

Fortunately, no one in Chelyabinsk was killed and most injuries were minor. Now, people in the area have a new hobby: hunting for meteorites.

These rocks may not look like much—just small pieces of gray stone—but there is something fascinating about them. Because while they may not have been sent by the gods, they are as old as our planet. And they came from outer space.

This article was originally published in the April 2020 issue.