This map shows the location of every asteroid impact since 2000 with an energy higher than 1 kiloton of TNT (the nuclear bomb that destroyed Hiroshima packed around 15 kilotons). The data are from the B612 Foundation, which tries to raise awareness of the dangers posed by asteroids, using information from a worldwide network of low-frequency microphones, designed to detect nuclear explosions and run by the Comprehensive Nuclear-Test-Ban Treaty Organisation. Such rocks almost always detonate high in the atmosphere, which limits the effects on the ground. But big ones can cause damage anyway: 1,500 people were injured in Chelyabinsk, in Russia, in 2013, after a 500 kiloton explosion 30km up. In 1908, 2,000 square kilometres of Siberian forest were flattened by a 10-15 megaton impact. Since Earth is mostly ocean and countryside, the odds of a strike on a city are fairly low. But the consequences could be disastrous.