Giant, extinction-sized asteroids hurtling into Earth may grab headlines and star in Hollywood blockbusters, but airbursts from smaller asteroids and comets are thought to occur once every 500-1,000 years, making them one of the most pressing threats to humanity from space.
That makes the discovery of an Antarctic airburst - a sort of austral Tunguska Event 481,000 years ago - a really big deal. Researchers working on the frozen continent discovered extraterrestrial debris layered in ice cores and strewn across the Transantarctic Mountains.
In their presentation this week at the Lunar and Planetary Science Conference in Texas, the researchers said the dust samples were scattered across 2,900 kilometers of Antarctica. The wide distribution of the material points strongly to an airburst origin.
Space rocks typically enter the atmosphere doing a crisp 40 to 60 times the speed of sound. Even when they don't hit the ground they can explode as they become superheated in the atmosphere. When that happens, the heat and shockwave keeps traveling toward Earth's surface. In the desert, such firestorms can leave behind huge swaths of glassy, melted sand. In Siberia in 1908, the Tunguska explosion tossed thousands of acres of full-grown trees to the ground like matchsticks.