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.
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.
Earth is constantly being bombarded with all sorts of things from space. The sun constantly smashes us with solar winds and radiation, asteroids are constantly making their fiery descents and every so often we’ll have one of our own bits of equipment come back down once its reached the end of its life (or sometimes, sooner). Thankfully our atmosphere does a pretty good job of breaking these things up before they reach the ground and most of the time debris from space lands in an unpopulated area, causing little to no harm. Still there’s evidence littering our planet that tells us that large objects from space make their way down to the surface, often with very deadly consequences.
Probably the most famous piece of evidence to support this, even though people don’t usually know it’s name, is the Chicxulub crater on the Yucatan peninsula. This is the crater that is currently believed to be responsible for the mass extinction event that happened approximately 65 million years ago, the one that wiped out the dinosaurs. The impactor, a fancy name for the asteroid that made that giant crater, was estimated to be about 10KM in diameter. The collision has been estimated to have a total energy output of something like 96 teratons of TNT, 2 million times more powerful that the largest nuclear weapon ever detonated. With that kind of power being unleashed it’s then very plausible that it was responsible for the extinction of many species.
The most recent example we have of something like this, although many orders of magnitude less severe, is the Tunguska event which happened in Russia back in 1908. Whilst not technically an impact from an asteroid (or comet, possibly), it is believed that the Tunguska asteroid exploded about 5~10KM above the surface, it still managed to level an area of over 2,000 square kilometres. That’s still powerful enough to take out a major metropolitan area however, so you’d hope that we’d have some strategies for dealing with potential events like this.
Turns out, we do.
Now many people would say “Why wouldn’t you just nuke the bastard” figuring that our most powerful weapon would be more than enough to vaporize a potential threat before it could materialize. The thing is though whilst nuclear weapons are immensely powerful they derive much of their power from the blast wave that they create upon detonation. In space however there’s nothing for them to create a blast wave with so much of the nuke’s devastating power is lost, leaving just the thermal radiation to do its work. Depending on the type of asteroid¹ it will either make the problem worse or simply do nothing at all.
The better option is something called a Gravity Tug, a specially designed spacecraft launched well in advance of the potential impact event to steer the asteroid off course. In essence they’re a simple idea the spacecraft simply approaches the asteroid and then stays next to it, using ion thrusters to keep a set distance between them. Whilst the gravitational effect of the spacecraft on the asteroid is minuscule over time it adds up to be enough to steer the asteroid away from its crash course with earth. Indeed this exact idea is being proposed to deflect the potential impactor Apophsis who’s got a small chance of hitting earth in 2036. Of course this only works for asteroids we know about but our tracking is good enough now that it’s quite hard for a potential disaster causing asteroid to slip through unnoticed.
When it comes down to it having an asteroid cause significant damage is a distinctly rare event with our first line of defence (our atmosphere) doing a pretty good job of breaking up would be impactors. Still it’s good to know that despite the vanishingly small possibility of such a thing happening we’re still prepared for it, even if it means having to launch something years in advance. Maybe we’ll eventually be able to modify that technology to be able to capture asteroids in our orbit so we could utilize them as bases for further operations in space. I’m not holding my breath for that though, but it’s a nice fantasy to have none the less.
¹There are 3 main types of asteroid. The first is basically solid rock compressed together, so the asteroid is one solid object. The second is a collection of rubble that’s held together by the tenuous gravity between all the small fragments. The last are iron asteroids which are solid lumps of metal, which are the really scary ones.