The speed of the object would make a difference too. Over the course of the past several months, 2012 DA14 has been clipping along at a brisk 17,450 mph (28,000 k/h), and that’s what packs it so full of energy. Just like a baseball that’s tossed lightly at your chest doesn’t hurt you but a fastball thrown by a pro player would crack your sternum, so too does velocity turn a nuisance rock into a unguided missile. But the speed of 2012 DA14, not to mention its angle of flight, saved our hides too. A difference of a few centimeters per second—faster or slower, depending on when and where the force was applied—would have been enough to shift the asteroid’s trajectory and put us in its crosshairs. A random bump from a smaller bit of space rubble could have done that trick, as could a gravity tug from a larger object the asteroid passed. So could the light of the sun.

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