NASA estimates that at least 95 percent of asteroids one kilometer (3,280 feet) or larger have been cataloged, with none posing a threat to Earth.
On July 25, an asteroid estimated at up to 450 feet across unexpectedly buzzed Earth at a distance of 40,000 miles, becoming the largest asteroid to come that close in a century.
The idea is that the impact will alter the trajectory of the smaller of the paired asteroids, which are now on track to pass close to Earth in 2022.
"The impact will blow off material to give [the smaller asteroid] an extra push, just like if you’re standing on a skateboard and you threw a baseball one direction, you’d move in the other direction," Fast says, adding that an asteroid coming our way would need to be deflected by only a tiny amount to keep it from hitting Earth.
Another potential way to deflect an asteroid is to use a so-called gravity tractor — a spaceship sent not to strike an asteroid but to use its own gravity to shift the space rock's trajectory — a concept credited to former astronaut Ed Lu, founder of the B612 Foundation, and astronaut Stan Love.
David Brin, a San Diego-based astrophysicist and science fiction author who serves as an adviser to the B612 Foundation, is confident that advanced technology will be able to protect the planet from a major asteroid strike like the one that did in the dinosaurs.
"As far as asteroid strikes go," he says, "we need to remember that the dinosaurs aren’t here because they didn’t have a space program."