Asteroids enter the Earth's atmosphere every day, but they rarely make it to the surface because they tend to break up first. An estimated 37,000 to 78,000 tons (33,565 to 70,760 metric tons) of material from space hits the Earth's surface every year, but most of it is in the form of dust-sized particles. Asteroids that would be large enough to threaten the Earth only happen once every million years or so.
More about asteroids:
- Asteroids and meteorites aren't the same thing. When the debris is in space, it's an asteroid; but once it hits the ground, it's called a meteorite.
- About once a year, an asteroid the size of a car hits the atmosphere, but these mostly just make large fireballs and then burn out before hitting the ground.
- The largest asteroids as measured by diameter are Ceres, Pallas, and Vesta, which have a mean diameter of around 591.5, 338, and 326 miles (around 952, 544, and 525.4 km) respectively.