A hundred million years sounds like a safe buffer, but the next one could happen at any time. But you can take it off your worry list – astronomers have it covered. A network of ground-based telescopes scans the skies for bits of rogue rubble larger than a few hundred meters. That's ample time to dust off the nuclear arsenals for an interception mission if we had to. Unfortunately, the Dr Strangelove approach creates lethal shrapnel travelling in the same direction as the original object; a smarter strategy is to send a spacecraft alongside it and gently "tug" it with gravity onto a slightly different trajectory.