On Oct. 7, 2008, just after midnight UTC, an asteroid 4 meters across came screaming into Earth’s atmosphere.  It started feeling pressure from the thin air around 100 kilometers above the ground. Traveling at a downward angle of about 20° at 46,000 kilometers per hour — a dozen times faster than a rifle bullet — the building pressure as it rammed through ever-denser air caused the gas in front of it to be violently compressed and heat up, so much so that the asteroid heated up as well. Both the air in front and the asteroid itself started to glow by the time it was 70 km above the Earth. Seconds later, around 42 kilometers and then again at 37 km up, it partially exploded, then one second later a final pulse of energy caused the asteroid to completely disintegrate.  The total energy released was equivalent to over a thousand tons of TNT exploding, much of that in the form of a debris cloud expanding away.…