On Saturday, astronomers discovered a new asteroid, just a few hours before it almost hit us. The asteroid is called 2016 QA2, and it missed the Earth by less than a quarter of the distance to the moon. That puts it about three times as far away from Earth as our farthest satellites. And we never saw it coming. So how did 2016 QA2 sneak up on us like that? For this particular asteroid, the answer seems to be that it has a very peculiar orbit. It's highly elliptical, which means it can usually be found hanging out by either...