Two Nasa astronauts say they have worked out a plan to stop an asteroid potentially colliding with Earth.
The US spacemen Edward Lu and Stanley Love propose sending up a huge rocket to "tow" away any such objects.
Their vehicle would simply hover over the asteroid and use gravity as a "towline" to move it out of danger.
A 20-tonne craft could safely deflect an asteroid 200m across in about a year of such "towing", Lu and Love report in the journal Nature.
Scientists believe that if an asteroid this size collided with the planet, it would cause widespread damage and loss of life.
Lu and Love believe that it would be extremely difficult to attach a spacecraft to the surface of such a rough and rocky body to push on it directly.
They argue that a spacecraft could simply use the gravitational attraction between itself and the asteroid to gently pull the hazardous object onto a safe trajectory.
The probe's thrusters would be angled away from the asteroid's surface so that they did not reduce the towing force, the BBC reports.