You’d have to be under a rock (ha!) to have not heard about the recent meteor that entered out atmosphere over Russia on Friday (which just so happened to be my birthday, what a present!). Thanks to the proliferation of cameras everywhere, predominately the dash cams which are common in Russia to avoid insurance scammers, the Chelyabinsk event was pretty well documented from multiple angles. If you had ever wondered what a decent sized asteroid air bursting in the atmosphere would look like and what it’d eventually do you couldn’t really get a better example, even from the wealth of smaller impacts that are witnessed every year.http://www.youtube.com/watch?v=duD0b1UMAnA
There’s been a lot of questions about this particular event and I caught a couple of them when I was reading through the comments on some of the videos. One of them that caught my eye was one asking why there appeared to be 2 contrails (I believe it was on this video). From what I can tell that’s probably some time after the air burst as it took the shockwave approximately 2 minutes to reach the surface after it occurred. Reports from various space agencies afterwards state that there was at least 3 probable impact sites which would corroborate my idea of it breaking up after the air burst. Not that there’d be a lot of it left after that however as it was rated at something like 500kt, about an order of magnitude higher than the first atomic bombs.
By far the most common question was how we could have missed something like this when we were quite capable of tracking a near-miss asteroid that just happened to pass by 15 hours later. There are a couple factors at play here but I’ll start with the most pertinent. For starters this is actually quite a small meteor with current estimates pegging its original size at somewhere around 17m² with a total mass of approximately 7000 tons. 2012DA14 was about 2~3 times the size and several orders of magnitude heavier (~190000 tons) making it a lot easier to spot. Secondly whilst we are capable of spotting asteroids like this prior to them entering out atmosphere we purposely limit ourselves to track the bigger ones since they have a much greater chance of causing extinction level events. With greater funding to NASA and related space agencies it would be possible to get more warning about things like this before they happen.
There would still be ones that we wouldn’t see coming unfortunately as depending on their make up and direction they come from they can be incredibly hard to spot. The Chelyabinsk meteor was, as far as we can tell, rocky and this tends have quite a low albedo which makes them quite difficult to track, especially if they come from certain directions where they won’t get much illumination. Large, primarily metallic asteroids are quite easy to track and the most devastating should they collide with us, but they’re also somewhat rare so the vast majority are simply larger rocky asteroids that have a decent albedo.
It will likely be a long, long time before we bear witness to something like this again. Whilst we’re likely to capture any event of note thanks to the proliferation of cameras everywhere there’s still an awful lot of this earth where us humans just aren’t present to see it and as such many events like this go completely unnoticed. It’s a shame really as they’re quite intriguing events and they can help us learn about what will happen should a larger asteroid cross our path one day.