Tunguska event

The five greatest balls of fire over Earth

The five greatest balls of fire over Earth

We live on a moving target in a cosmic firing range. Each day, the Earth is bombarded by about a hundred tonnes of space debris. It may sound alarming, but this is really nothing to worry about. Most of the objects that fall towards our planet are pretty small – typically about the size of a grain of sand or even smaller – and burn up in the upper atmosphere tens of kilometres above the ground.