It could be decades or more if the asteroid is large and its closest passes are still distant. Or it could be no time at all, as the Chelyabinsk asteroid demonstrated. If an asteroid is detected only a year or two in advance of a collision, about the only option for reducing casualties involves civil-defense measures such as evacuations, researchers say.
How dangerous are near-Earth asteroids? 5 key questions answered.
On Feb. 15, asteroid 2012 DA14, discovered a year ago, cleared Earth by a scant 17,200 miles. The same day, a smaller, unrelated asteroid that no one saw coming exploded 12 to 15 miles above Russia’s Chelyabinsk region. Events that day highlight the risk that near-Earth objects (NEOs) can pose – although to some extent, humans can counter them.
