How low can they go? Meteors, that is

摘要

Great balls of fire rip through Earth's atmosphere every day-but guessing which will hit the ground has been a challenge. Now, a model predicts how high up each incoming space rock will be when it bursts into flame - and whether people on the ground should look out for shrapnel. When space rocks are unlucky enough to cross paths with our planet, friction in the atmosphere bakes them up and turns them into fireballs. Most of the time, this happens high enough that they don't pose a threat, burning up totally before nearing the ground. "Our atmosphere provides an effective shield against these otherwise dangerous projectiles," says Manuel Moreno-Ibanez of the Autonomous University of Barcelona in Spain.