Throw a Few Fastballs
Remember those baseball pitching machines you faced when you were a kid? They had a feeder tube and a wheel assembly to shoot the balls out at 50 to 60 miles (80 to 97 kilometers) an hour. Wouldn't it be great if you could set up a pitching machine on an asteroid? Not to take batting practice, but to save the world?
As crazy as it sounds, astronomers have an idea to do just that. They call their machine a mass driver, but it works the same way. It scoops up rocks from the surface of an asteroid and hurls them out into space. With each throw, the machine applies a force to the rock, but the rock, thanks to Newton's action-reaction law, applies a force back to the machine -- and to the asteroid. Throw a few hundred thousand rocks, and you'll actually shift the asteroid's orbit.
Of course, the concept has invited some criticism. How do you get the mass driver on the asteroid? And how do you keep it powered? A pitching machine plugs into an electrical supply, but extension cords are tough to manage out in space. And what if the darn thing breaks down? A relief pitcher may not be available to finish the game.
Maybe baseball is the wrong sport. Maybe another backyard favorite offers a better solution.