Fears about an “Armageddon”-like space rock collision have prompted the United Nations to create an International Asteroid Warning Group and a plan for deflecting an incoming asteroid.

Respected scientist-astronauts have been saying it for years: We need to prepare. But before the UN General Assembly approved new measures this month, no country had even been on the lookout for asteroids that might be on course to hit earth, Scientific American reports. As one Apollo astronaut, Rusty Schweickart, put it: “If we don’t find it until a year out, make yourself a nice cocktail and go out and watch.”

Planetary protection apparently isn’t just a job for Bruce Willis. The threat is real. And, actually, “deep impact” has happened before.

In 1908, a meteorite exploded over a place called Tunguska in a remote part of Siberia. For decades no one was quite sure what flattened trees for miles around but caused no crater. Scientists later discovered the rock fell so fast (around 33,500 mph) and got so hot (44,500 degrees Fahrenheit) that it simply exploded several miles above the earth with the force of hundreds of atomic bombs.

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