Space is out to kill you. There is no way to stem its aggression. But it's usually an incompetent killer, so don't freak out.

The last thing residents of Chelyabinsk, in central Russia, expected on Friday was to see a flaming fireball from the heavens hurtle towards their industrial city. On-scene accounts make it seem like an angry deity enacted His vengeance for some unknown slight. The meteor was actually unrelated to the 2012 DA14 asteroid near Earth, according to NASA. (Which, by the way, you can watch soar by.) But 1,000 Russians were injured from the concussive blast and flying, shattered glass.

All the advanced air defenses that humanity has invested in? The interceptor missile that are (sometimes) able to stop an adversary missile from impacting? The early-warning monitoring systems that are supposed to give humanity enough time to plan a response? They are useless, useless against a meteorite onslaught. Do not believe the stories about the Russians shooting the cosmic rock down.

"The reason, simply put, is physics," explains Brian Weeden of the Secure Earth Foundation, a former captain and missile expert in the U.S. Air Force Space Command. Asteroids orbit the sun like Earth does, and occasionally our orbits intersect, causing the rocks to enter the atmosphere as flaming meteors screaming toward impact. They are not flying like airplanes and missiles that air defenses target. Shooting them will not change their speed or trajectory – at best, a missile impact might change its direction somewhat or shatter it into more pieces.

But let's say that happens. What then? "Now you've got a shotgun blast instead of a single shot," Weeden explains, and "all those pieces are still traveling in the same direction and at the same velocity." Gulp.

Still, it's vanishingly unlikely that air defense systems would be able to even make the shot. The Chelyabinsk meteor was traveling at something like 32,000 miles per hour. (A 747's typical cruising speed? 567 miles per hour.) By the time you notice it, it's too late to stop it.

Not that you would notice it. Meteors like the one in Chelyabinsk are going to pass through the detection systems that humans have. Telescopes pointed to space are only going to be able to see a ginormous asteroid. Missile warning and air-defense radars run via software that ignores things that aren't planes and missiles. And the eyes of U.S. military satellites are pointed the wrong way – down toward Earth. The Defense Support Program satellite constellation, for instance, is looking for launches of things like intercontinental ballistic missiles that threaten America, using infrared. But the asteroid is cold until it enters the atmosphere.

And in this case, the asteroid was relatively small, maybe eight to ten tons. The asteroid tracking networks – run by NASA, the European Space Agency and bands of amateurs – are looking for massive space rocks, some the size of moons, and calculating their potential intersection with Earth. That process can provide early warning – years and decades out. Something small enough to slip into the atmosphere like this one is unlikely to be detected. And there's not a weapon forged by man that could do something about it anyway, short of calling Bruce Willis.

But there's good news. Space rocks are lousy shots. The Earth is mostly ocean and uninhabited areas. The frequency of meteorite impacts is correlated with size, Weeden explains, and the smaller the meteorites, the more often they land. "But the places where people are is actually pretty small," he says. Even the injuries that occurred at Chelyabinsk were mostly concussions and accidents from shattered glass, not from the meteorite itself. Close but no cigar, space: "Your odds of dying by a meteor are pretty damn small. You're thousands of times more likely to die by car on way to work."

Believe it or not, there is actually a United Nations team convening to spare Earth from the ravages of space. Weeden just met with it in Vienna a few days ago, and its meetings are ongoing. And it has a plan.

Within the United Nations Special Committee on the Peaceful Uses of Outer Space is a subcommittee on science and technology. That subcommittee has an ad hoc advisory team of dozens of space experts from around the world who try to "figure out how to coordinate detections, warnings and response, and possible deflection" of asteroids that might impact Earth, Weeden says. They're mostly focused on the big asteroids, the ones larger than 100 meters in diameter or bigger. And among their ideas – the one that "physics says should work," in Weeden's phrase – is something called a Gravity Tractor.

The idea is to launch a spaceship near a nefarious asteroid. The presence of the spaceship's inherent gravitational field should impact the asteroid's, to the point where it might be able to shift the asteroid's trajectory and get it to avoid the path of Earth's celestial journey. It's untested – and apparently it won't even host astronauts: it's unmanned, so Bruce Willis can take a knee. But Weeden has faith the Gravity Tractor will work. Here's a simulation. (It's worth mentioning that other proposals include Armageddon-style nuclear detonations, laser-beam pushes and even attaching a big-ass cordto pull the thing out of the way.)

Oh, and the name of that United Nations advisory group that came up with the Gravity Tractor? It's called Action Team 14. "They're not superheroes," Weeden helpfully clarifies. But right now, superheroes are the only defense Earth has against falling space rock.