Have you ever considered that we are living is a ballistic cross fire zone. In fact at slow rate of a catastrophic
missile
every millions of years, this threat always losses attention. Yet that one-in-a-million is truly devastative and it''''s always a worthy talk point.
Every now and then planet earth comes into the crossfire of
galactic missile shooting between Sun and the rest of the universe (Kuiper belt mostly). However the big ones come very rarely - mostly shielded by Jupiter. Yet if it hits it will be far more disastrous than anyone can ever imagine. Those paleontology lovers must be still be wondering whether fate of the Dinosaurs was decided by this phenomena. Many sci-fi lovers must have loved Arthur C Clarke novel Hammer of God which discusses the matter in detail.
However I have collected so many ideas that people have brought forward. Let me note few here.
- On-board-Nuke blast to blow it
- Near proximity nuke blast to slow down
- "Galactic billiards" or another words, move a smaller one to make a collision path with the dangerous one. You can do this iteratively to achieve great success.
Now another idea has come - Gravity Tractor. Have a read.