The first word of the incoming missile would likely come from one of three main observatories NASA has assigned to scan the sky for cosmic ordnance all day, every day. But amateurs and academic observatories around the world could spot it too (it was an amateur who discovered 2012 DA14, in fact). We also might not see it at all. Like fighter planes taking advantage of natural blind spots in the sky, asteroids can approach from the direction of the sun, making them impossible to see until it’s way too late. “The smaller ones aren’t even visible until they’re on the way back out,” says Don Yeomans, head of the NEO office.

Read more: [link to science.time.com]