Gravity Tractor

Cool!

A Gravity tractor is a spacecraft that deflects another object in space, typically a potentially hazardous asteroid that might impact Earth, without physically contacting it, using only its gravitational field to transmit the required impulse. The tractor spacecraft could either hover near the object being deflected or orbit near it. The concept has the advantage that essentially nothing need be known about the mechanical composition and structure of the asteroid in advance.

(HT Best of Wikipedia)