As the US government ponders a strategy to deal with threatening asteroids, a dramatic explosion over Indonesia has underscored how blind we still are to hurtling space rocks.
On 8 October an asteroid detonated high in the atmosphere above South Sulawesi, Indonesia, releasing about as much energy as 50,000 tons of TNT, according to a NASA estimate released on Friday. That's about three times more powerful than the atomic bomb that levelled Hiroshima, making it one of the largest asteroid explosions ever observed.
However, the blast caused no damage on the ground because of the high altitude, 15 to 20 kilometres above Earth's surface, says astronomer Peter Brown of the University of Western Ontario (UWO), Canada.
Brown and Elizabeth Silber, also of UWO, estimated the explosion energy from infrasound waves that rippled halfway around the world and were recorded by an international network of instruments that listens for nuclear explosions.
The explosion was heard by witnesses in Indonesia. Video images of the sky following the event show a dust trail characteristic of an exploding asteroid.
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