Yes, a killer asteroid could hit Earth
đFirst Spaceâď¸Earth is in a constant game of celestial bumper cars, colliding withâand obliteratingâthe 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 Âdinosaurs.) NASAâs 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 Âexplode in midair, like one did over Chelyabinsk, Russia, in 2013. There wasnât enough shrapnel to leave a crater, but the sonic boom did blast out windows. So how much havoc could larger rocks wreak?
Diameter 3,300 ft.
Lights out:Â This debris could throw enough dust to block out the sunâglobally.
Impact energy 0.01 MT
Chelyabinsk:Â Russiaâs airborne explosion was 20â30 times more powerful than Hiroshima.
Impact energy 1 MT
Kaboom:Â Equals about 11,000 tons of TNT. The Eiffel Tower weighs around 10,000.
100 million Avg. years between impacts:
The dino killer:Â These can obliterate nearly all lifeâbut 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 fastâÂupwards 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 itâs 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 sortâwhich make up 94Â percent of all meteoritesâfall 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.