Armageddon

The movie Armageddon shows a giant asteroid on a collision course for Earth. Somehow the asteroid avoids detection until 18 days before it will hit the planet. In the movie, they solve the problem by landing spacecraft on the asteroid and splitting it in two with explosions. This sends the two halves away from Earth and saves the planet. How realistic is all of this?

Here's the bad news. Asteroids and space debris do come into contact with Earth on a regular basis. The most recent event like this happened in 1908, when an asteroid passed by Tunguska, Siberia. Without even hitting the ground, that object flattened 800 square miles of forest. But the vast majority of objects that head towards Earth are very small, and burn up as they pass through the atmosphere. Almost none of them do any damage at all.

Now, here's the good news. No known object the size of an asteroid is currently known to be heading towards Earth. Scientists estimate that a comet or asteroid big enough to cause damage to the whole planet comes into contact with the Earth only once every 50 to 100 million years. There are several organizations that are dedicated to mapping and tracking Earth-orbiting objects, including NASA's Near Earth Object Program and Spacewatch at the University of Arizona. These organizations do two main things: they catalog the objects orbiting Earth, and they study all of the known objects to see if any are likely to set a course for Earth. Most recently, the Spacewatch program ruled out the possibility of an asteroid known as 2004 MN4 hitting the Earth in the year 2029.