The Chicxulub asteroid is probably the most famous space rock in the world. Although you may not know its name, its impact 66 million years ago is legendary – causing a mass extinction event that saw most non-flying dinosaurs and many other species wiped out.Impacts from such large asteroids are immensely rare, but small- and medium-sized rocks are far more common in the Solar System and can still do serious damage.These asteroids sometimes reach the ground, but even those that disintegrate in Earth’s atmosphere – like the one that caused the Chelyabinsk event in 2013 – can create explosive airbursts, with resulting shockwaves that may shatter glass, damage buildings and injure anyone who happens to be nearby.ESA's Planetary Defence Office conducts regular observation campaigns to look for risky space rocks, predict their orbits, produce impact warnings when necessary and is involved in potential mitigation measures.