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View Diary: BREAKING: Meteor airburst over Chelyabinsk (318 comments)

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    Have you ever seen the Mythbusters episode where they tested how deep you have to be underwater to be safe from bullets, and some of the bullets from some weapons basically disintegrated when they hit the water?

    Same principle. Something hitting the atmosphere at multiple tens of kilometers per second is like slamming into a semi-solid. The air can't get out the way fast enough so the pressure on the front of the object builds  up higher and higher. If the object is small and fairly solid, the object is able to withstand the pressure long enough for the pressure to slow it down, and it falls as a meteorite at terminal velocity.

    If the object is massive and internal weak enough enough, the pressure can't slow it down before the object's internal structure fails, which causes it to disintegrate, and then the smaller fragments hit that same pressure, and being smaller have even less ability to withstand it,  and they disintegrate and so on and so on. Since all that kinetic energy has to go somewhere, you get an explosion which can reach nuclear weapon scales. It's estimated that there's kiloton level explosions in the upper atmosphere maybe once a month or more.

    How high an airburst happens (if it happens at all) depends on the makeup of the object, its mass, and its density.

    All this wasn't realized until the 1960s when the Vela satellites, meant to detect nuclear detonations, started reporting nuclear-level explosion in the upper atmosphere that clearly didn't come from nuclear tests. It was a legitimate concern during the latter stages of the Cold War that if something like Tunguska (or even today's event) happened near a strategic target, the default assumption would be a nuclear attack and World War III starts.

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