  We present a novel concept to impart a continuous thrust to an Earth
threatening asteroid from a hovering spacecraft without need for physical
attachment nor gravitational interaction with the asteroid. The concept
involves an ion thruster placed at a distance of a few asteroid diameters
directing a stream of quasi-neutral plasma against the asteroid surface
resulting into a net transferred momentum. As the transmitted force is
independent of the asteroid mass and size the method allows deflecting
subkilometer asteroids with a spacecraft much lighter when compared to a
gravity tractor spacecraft of equal deflection capability. The finding could
make low-cost asteroid deflection missions possible in the coming years.
