“Wouldn’t it be silly if we got wiped out because we weren’t looking?” said Edward Lu, a former NASA astronaut and Google executive who leads the detection effort. “This is a wake-up call from space. We’ve got to pay attention to what’s out there.”

Astronomers know of no asteroids or comets that pose a major threat to the planet. But NASA estimates that fewer than 10 percent of the big dangers have been discovered.

Dr. Lu’s group, called the B612 Foundation after the imaginary asteroid on which the Little Prince lived, is one team of several pursuing ways to ward off extraterrestrial threats. NASA is another, and other private groups are emerging, like Planetary Resources, which wants not only to identify asteroids near Earth but also to mine them.

“Our job is to be the first line of defense, and we take that very seriously,” James Green, the director of planetary science at NASA headquarters, said in an interview Friday after the Russian strike. “No one living on this planet has ever before been hurt. That’s historic.”