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In Alastair Reynolds' Revelation Space, the lighthugger Nostalgia for Infinity used a kinetic energy weapon to destroy the northern pole of a planet

There was -- where previously there had been nothing -- a tiny red-hot smear near the edge of Resurgam's northern polar cap, like a foul rat's eye in the crust of the world. It was darkening now, like a hot needle just pulled from a brazier. But it was still hurtingly bright, darkening less through its own cooling than because it was being progressively shrouded by titanic veils of uplifted planetary debris. In windows which opened fleetingly in the curdling dark storm, Khouri observed dancing tendrils of lightning, their bright ignitions strobing the landscape for hundreds of kilometres around. A near-circular shockwave was racing from the site of the attack. Khouri observed its movement via a subtle change in the refractive index of the air, the way a ripple in shallow water caused the rocks below to acquire a momentary fluidity of their own.

Apparently, this weapon was one of the weakest on the ship.

Then they pulsed a bloodier red, and status graphics informed Volyova that the ship's orbital-suppression elements -- almost the puniest weapons system it could deploy -- were now activated, armed, targeted and ready

How much energy would be required to create such large destruction? Could kinetic energy bombardment from a spaceship (the lighthuggers were a few km in length) be powerful enough?

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From this useful table we know the energy that the famous Dinosaur killer had

5.43 × 1023J -120 Tt TNT: 1 Chicxulub Crater = 1 Dinosaur Killer = 20 Shoemaker-Levys

Calculating the energy of kinetic weapon is fairly easy: its 0.5 x mass x velocity2. So to make huge boom, you need very heavy bullet that moves very fast.

Since we can't move anything faster than the speed of light, lets look at the "relativistic weapon" from the same table:

5.5 × 1014J -132 ktTNT Relativistic weapon: 1 gram at 99% c

So to get the missing 109 Joules we need to get 2x109 grams which is 20,000 Tons if my math is right, which would require bullet made of osmium the size of 885.35 cubic meters.

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