Gravity’s rainbow, indeed. It’s hard not to be impressed—if not downright terrified—by the screaming meteorite that buzzed Russia last week, and only a day before an asteroid the size of an apartment building passed us with only about 17,000 miles to spare (for reference, the Moon is about 250,000 miles away). And it turns out, those weren’t the only two attacks from on high last week: there was a fireball over California and another one over Cuba. Somebody up there really hates us, it seems. But is all this seemingly apocalyptic activity that unusual? From his new perch over at Slate (formerly at Discover), Phil Plait explains in his excellent Bad Astronomy blog that despite the rumblings via social media and elsewhere, all of these events are not connected. (That sequence at the beginning of the loathsome disaster flick Armageddon, where the big meteor hit is preceded by a spate of smaller hits, is, like so much else in the movie, not the way things would really happen.) First, about that asteroid, officially dubbed asteroid 2012 DA14. At 17,000 miles, that’s the closest a rock of that size has come to us, or at least one of which we saw coming. And we have a pretty good idea where all the Big Ones are, and we’re generally safe for the far foreseeable future. Fortunately, the ones we can’t see coming are too small to have any kind of dinosaur-extinction-esque effects, although they would ruin your day. So while DA14 wasn’t an especially huge asteroid, if it hit the Earth, Plait tells us, the impact would be akin to setting off 20 million tons of TNT. That wouldn’t wipe us out as a species, but still it wouldn’t be a very good thing. For comparison, the Russian rock—dubbed the Chelyabinsk meteor—generated “a series of explosions that totaled something like 30,000–500,000 tons of TNT.” The phrase “not in my backyard” has never been more apt. The universe is a dangerous place, and there’s all sorts of stuff up there. Asteroids* are whizzing around the Solar System willy-nilly, and there are plenty of Earth strikes—every time you see a shooting star, that’s one of them. Fortunately, they’re all pretty tiny.  That said, it’s actually pretty difficult for these things to hit the Earth, as we’re a moving target: the Earth moves in its orbit at a speed of 18 miles per second. So for anything substantial to hit us, it would be quite the coincidence. (If you play pool as poorly as I do, you kind of get the picture.) By the way, annual “meteor showers” like the Perseids occur because the Earth happens to pass through a relatively stationary cloud of debris every year. It is also an object lesson (a large, fiery, apocalyptic object at that) in statistics. Plait explains:

In science, there’s an event called a stochastic process. It happens when you have a system that follows a set of rules, but there's a random nature to it as well, making it hard to predict exactly how things will turn out. Flip a coin 10,000 times and there’s no way I can tell you what each flip will be, but I can be very confident you’ll get close to 5000 heads and 5000 tails. Asteroid impacts are a stochastic process. We know that a near pass by something the size of DA14 only happens once every 40 years. On average. We know something the size of the Chelyabinsk rock hits us once every century. On average. We know a fireball like those seen over California and Cuba happen once a week or so. On average.

So the odds of getting heads or tails in any given coin flip are 50/50—but there is nothing preventing any coin flipper from getting five heads in a row. It is curious that these events spurred Congress into action, and there is the hope that it will mean more money for space exploration, be it via NASA or private enterprise. I am not especially worried about an Armageddon-size object hitting us, but as the results of the Russian rock indicate, even the small ones can do some damage and cause some injury. And, as they say, you never hear the one with your name on it.   *For those who don’t remember grammar school science class, here is the difference. An asteroid is any large rock in space smaller than a planet, and which does not have an atmosphere. Asteroids can be tiny, or they can be quite large; Ceres, the largest asteroid in the Solar System, has a diameter of about 975 km and has actually been labeled as a “dwarf planet,” but let’s not go there. A meteor is an asteroid that enters the Earth’s atmosphere and burns as it vaporizes. Should bits of the meteor make it to the ground, it would then be called a meteorite. So the rock that rocked Russia was an asteroid until it hit the atmosphere, at which point it became a meteor, and the surviving chunks, which likely ended up in a lake west of Chelyabinsk, should they be recovered, are meteorites.