asteroid hitting earth
Asteroid smackdown. Shutterstock

Earth is in a constant game of celestial bumper cars, colliding with—and obliterating—the relatively puny space rocks that dare cross its path. The planet is still standing after 4.6 billion years, but a modern collision could devastate cities, continents, and even life itself. (Just ask the ­dinosaurs.) NASA’s Center for Near-Earth Object Studies keeps watch on more than 18,000 potential troublemakers, ranging from just 3 feet to more than 3,000 feet across. Meteorites smaller than 100 feet usually ­explode in midair, like one did over Chelyabinsk, Russia, in 2013. There wasn’t enough shrapnel to leave a crater, but the sonic boom did blast out windows. So how much havoc could larger rocks wreak?

Size really does matter

Diameter Impact energy (MT) Avg. years between impacts
16 ft. 0.01 1
33 ft. 0.1 10
80 ft. 1 100
160 ft. 10 1,000
460 ft. 300 20,000
1,000 ft. 2,000 70,000
2,000 ft. 20,000 200,000
3,300 ft. 100,000 700,000
3 miles 10,000,000 30 million
6 miles 100,000,000 100 million

Diameter 3,300 ft.

Lights out: This debris could throw enough dust to block out the sun—globally.

Impact energy 0.01 MT

Chelyabinsk: Russia’s airborne explosion was 20–30 times more powerful than Hiroshima.

Impact energy 1 MT

Kaboom: Equals about 11,000 tons of TNT. The Eiffel Tower weighs around 10,000.

100 million Avg. years between impacts:

The dino killer: These can obliterate nearly all life—but our odds look good.

Need for speed

One reason these flying objects are so dangerous is their velocity. A zippier asteroid can do more damage. And these things are fast—­upwards of 44,000 miles per hour. All other factors (size, angle of entry, target) being equal, a faster asteroid can dig a bigger crater, and melt the rock it’s slamming into.

Tough stuff

Composition is key. Metal asteroids are durable enough to reach the surface even at small sizes, while carbon-rich rocks almost always break up in the atmosphere. The stony sort—which make up 94 percent of all meteorites—fall somewhere in between. But even a broken-up hunk of space junk can cause a dangerous shockwave in transit.

Location is everything

More than 70 percent of Earth is ocean. If an asteroid happened to make a water landing, it might be less harmful than if it struck populated land. Experts do have some (minor) concerns about a tsunami, which occurs when large amounts of water get displaced, but the real worry is a high-speed projectile launching dust from the seafloor high into the atmosphere.

This article was originally published in the Winter 2018 Danger issue of Popular Science.