When a meteor exploded over Chelyabinsk, Russia, last February, the world's space agencies found out along with the rest of us, on Twitter and YouTube. That, former astronaut Ed Lu says, is unacceptable—and the United Nations agrees.

In October the U.N. General Assembly approved a set of measures to limit the dangers of rogue asteroids. The U.N. plans to set up an International Asteroid Warning Group for member nations to share information about potentially hazardous space rocks. If astronomers detect a threatening asteroid, the U.N.'s Committee on the Peaceful Uses of Outer Space will help coordinate a mission to deflect it.

Lu and other members of the Association of Space Explorers (ASE) had recommended that the U.N. take those first steps toward addressing the problem of wayward asteroids. The ASE has also asked the U.N. to coordinate a practice asteroid-deflection mission to test the technologies for pushing a rock off course before such tactics become necessary.

The ASE urges that each country delegate asteroid duties to a specific internal agency. “No government in the world today has explicitly assigned the responsibility for planetary protection to any of its agencies,” said ASE member and Apollo 9 astronaut Rusty Schweickart during a public discussion in October at the American Museum of Natural History in New York City.

The next key step in defending Earth is to identify the menacing objects. “There are about one million asteroids large enough to destroy New York,” Lu said at the meeting. “Our challenge is to find these asteroids first, before they find us.”

The B612 Foundation, a nonprofit Lu created to tackle the problem of asteroid impacts, is developing a privately funded space telescope called Sentinel. The telescope's sensitivity to infrared light—the heat given off by objects warmed by the sun—should enable it to spot a large number of truly menacing asteroids, but smaller bodies, such as the one that hit over Chelyabinsk, will remain mostly unseen.

Early detection is important because it increases the chance of being able to deflect a giant asteroid before impact. If a spacecraft were rammed into an asteroid five or 10 years before the rock was due to hit Earth, the slight orbital alteration should be enough to ensure a miss.

The impact over Chelyabinsk, which injured 1,000 people, was a warning shot, American Museum of Natural History astronomer Neil deGrasse Tyson said at the discussion. Now it's time for Earth's citizens to take action.