why, if a big enough meteor hits the earth, is the impact like a nuclear bomb?

Question

why, if a big enough meteor hits the earth, is the impact like a nuclear bomb?

In: 1

Answer 1

It isn’t exactly like a nuke, but they’re similar simply because both release huge amounts of energy.

The Tsar Bomba, the largest nuclear weapon ever made by mankind, released about 50 megatons of energy (that is, it released as much energy as blowing up 50 million tons of TNT at once). An object hitting Earth from space necessarily hits Earth with at least Earth’s escape velocity of about 8 km/s, so if we use the formula for kinetic energy:

E = (1/2) m v^2

50 megatons TNT = 1/2 m (8 km/s)^2

we find that an object of mass m = about 3 billion kg would hit Earth with the same energy as was released by the Tsar Bomba. (In practice, since they’re usually going faster than this, you can get away with slightly smaller objects.) That sounds like a lot, but it’s roughly the mass of the Great Pyramid at Giza: big, but well within reach of even smaller objects in space.

A typical comet is about a thousand times that mass, meaning that it impacts with the energy of a thousand of mankind’s largest nukes going off at once.

EDIT: I had Earth’s escape velocity wrong – it’s ~12 km/s, not 8. But the broader idea stands.