A Gravitational Tractor for Towing Asteroids

Such a title would have been immediately considered as science-fiction some years ago, but knowledge and technology rapidly evolve. Edward T. Lu & Stanley G. Love have written a paper where they expose a method to get rid of nasty asteroids:

We present a concept for a spacecraft that can controllably alter the trajectory of an Earth threatening asteroid using gravity as a towline. The spacecraft hovers near the asteroid with thrusters angled outward so the exhaust does not impinge on the surface. This deflection method is insensitive to the structure, surface properties, and rotation state of the asteroid.

Read this paper (pdf - to be published in Nature).

Oh and the asteroid shown in the image below is 25143 Itokawa as seen from Hayabusa, a japanese spacecraft launched in may of 2003 that is supposed to collect a sample of material from this asteroid and bring it back to Earth for analysis. On november 7, Hayabusa was 7.5 km from Itokawa. You can follow almost in real time the state of the mission on this page.

25143 Itokawa on wikipedia
Hayabusa on wikipedia
Hayabusa arrived at Itokawa - sept. 14th, 2005 (pdf)
Proximity operations + beautiful pictures of the asteroid