Lu and Love suggest a way that doesn't involve landing on an asteroid at all. In a hypothetical scenario, they describe a 20-ton ship, with a mass similar to a city bus, approaching an asteroid 200 meters in diameter.

The relatively weak gravitational force between both objects — about the force of grasping one apple — would bind them.

To keep from colliding with the asteroid, the rocket ship would turn on its thrusters, which would be angled to the sides of the asteroids instead of directly at the surface.

This would reduce the amount of dust stirred up and the actual energy needed to eventually change the asteroid's speed.

With the thrusters on, the spacecraft would essentially hover above the asteroid and slow it down. Even a tiny change in velocity years before impact would result in a big miss down the road.

"All you do is maintain a parked distance and pull the asteroid along," said Dan Durda, senior research scientist at Southwest Research Institute in Boulder, Colo., and an expert in asteroids.

"This idea can make use of the same nuclear-electric propulsion technology that you're using to go and do other exploration in space."

In fact, Lu and Love sketched out their plan based on spacecraft that were under development by NASA in the Prometheus program, which was focused on building ships with nuclear-electric propulsion systems to accomplish long-distance missions such as landing on Mars or on some of Jupiter's moons.

The program is currently on hold, but according to Lu, NASA could use a more modest spacecraft to redirect Apophis using the gravitational tractor design, should future space surveys currently underway determine that an impact is inevitable.