In 1908, a huge fireball streaked across the sky and exploded a few kilometers above the Earth’s surface, downing trees for miles and miles around but leaving no impact crater on the ground. This mystery was known as the Tunguska event.
But how did this happen? The amount of energy released was estimated to be somewhere between 5 and 30 Megatons of TNT. (Comparably to a “typical” hydrogen bomb.) What could’ve caused this devastation?
My answer: a large meteor or small asteroid/comet could have done this easily. How? Let me explain.
When a meteor enters Earth’s atmosphere, it’s moving very, very quickly relative to the Earth. Meteors have a speed relative to Earth anywhere between about 40,000 and 260,000 kilometers-per-hour (11 to 72 kilometers/second), which is incredibly fast. The Earth’s atmosphere works — through friction — to slow this meteor down, heating it up and causing it to glow.
But if there’s a lot of ice and/or frozen carbon dioxide in this meteor, it’s going to heat up and start to boil. If you have a solid piece of rock with a cavern of boiling water inside, it’s only a matter of time before the pressure builds up enough to cause a powerful explosion.
If I assume my meteor moves at the maximum speed its allowed, 260,000 kilometers-per-hour, I can figure out how massive it needs to be to produce 10 Megatons (4 x 1016 Joules) of energy. The answer? A little over 1,000 tonnes, which means it was probably a rock a little less than ten meters on each side. Which means it was about the size of the smaller rock to the left of Haystack Rock in this picture.
And physics will take care of the rest: convert that kinetic energy into heat energy, use that heat to boil liquid inside, and — just like it did for the mythbusters — the increased pressure will cause the explosion we’re all looking for. And the only scientific principle you need to know to make this possible? The conservation of energy.
And that’s it. Plain-and-simple, how simply hurtling through the atmosphere, if you’re filled with something that can boil, can cause you to explode with a tremendous amount of energy. And there’s no faking that.