You might have shrugged. Maybe you yawned. But when Asteroid 2015 TB 145 screamed by at 20 miles a second it certainly didn’t raise too many eyebrows… except to note that its appearance on Halloween night seemed like an invitation for an obligatory Holiday reference. The Great Pumpkin Asteroid? At nearly half a mile wide and as close as our Moon, it could’ve been the ultimate in Tricks or Treats.
Every so often, we’ll be alerted to a similar encounter, but we don’t tend to give much notice. We’ve been paying at least passing attention to the objects flying around our sky for around four hundred years or so, but so far none that are big enough have come close enough to worry about. You’d be tempted to believe that none ever will.
Asteroid 2015 TB 145, aka The Halloween Asteroid
Discounting the fact that I'm a worrier, here are two other reasons I stop and think about it. First, there’s Murphy’s law, a popular variation of which is “Whatever can go wrong, will go wrong.” - given enough time, at least.
Every now and then, I’ll break down and play the lottery. My intelligent friends mock my occasional hopeless bet… While I know they’re right in a way, I also know that eventually, someone wins. See, I’ve always been fascinated with the idea that any phenomenon that has a small, but finite probability, is guaranteed to happen if you take enough chances (i.e., wait long enough). If you're skeptical, just take a look at the lunar surface to see how many times it’s been smacked by sizable debris. Sooner or later despite the incredible odds, somebody wins, or in this case, loses.
The second reason I tend to worry is that if at some possibly distant future time we get to experience an encounter with a major asteroid, we won’t see it in time to do anything about it. To guard against a catastrophic event, it requires a long term view. You'd need to have detected the object and predicted its path in time to intercede. And you'd have to have a capability ready to divert it - a capability that might take a decade to conceive, build and test.
The Halloween Asteroid was first detected on the 10th of October, only three weeks before it sailed by us at a 'safe' distance.