Some Things Asteroidal


The Darkest Side of Saturn is, among other things, an asteroid story—an astronomer and an engineer co-discover a two mile wide asteroid that might or might not hit the Earth in 16 years. Their conundrum (besides the potentially illicit affair between them) is how to announce it without making jackasses of themselves.

Since the story is about a fictional dangerous asteroid, and since we know that real asteroids present the Earth with problems now and then, I’ll say a little about them here. If you want to either put your mind at ease or scare the b’Jesus out of yourself—depending on how paranoid you are—read on.

Do we need to worry about an asteroid collision?

In a word—NO. It’s not something you need to lose sleep over. If you allow a few more words, it’s a very low probability but very high consequence event. It’s like that old fighter pilot’s saying about flying: “99% boredom, 1% stark terror,” except for large asteroids it’s more like 99.999… (and more digits) boredom, and a teeny tiny little bit of really stark terror.

If a two mile wide asteroid like the one in the book hit, the explosion would be like detonating the whole world’s nuclear arsenal, except nearly a hundred times larger. It would likely induce “asteroid winter”, causing crop failures and 100 times more deaths than from the direct blast alone. Hundreds of millions—maybe even billions of people—including you and everyone you know—could die of starvation and wars because of the collapse of civilization.

So, it’s not likely to happen, particularly in the short term, but over the long term the odds go up. If we wait long enough, we will be hit, the question is whether it’s in tens of years, or thousands, or millions, or longer. For the big ones, it’s millions, like the six mile wide asteroid that killed the dinosaurs. But then, that was 65 million years ago. Are we overdue? To paraphrase Ray Bradbury, “Does something wicked this way come?”

Regardless, if we find one with our name on it in the short term, small or large, we better do something about it. That brings up the next question:

If an asteroid impact is predicted, what could we do and how much time would we need?

We’d need lots of lead time. It takes a few years to build and launch a spacecraft and a few more years to get there and do something. For some asteroids, like Bennu (500m wide), we already know the risk more than 150 years out. It’s about a 1:1000 probability of impact in the last part of the 22nd century. We won’t have to worry about it, but the children of our great-great-great grandchildren might.

Others might pop up with less warning. If it were a really big one, say over a kilometer diameter, we’d probably need at least 15–20 years to do something about it—even earlier would be better. We’d want to deflect it. We’d want to send a spacecraft out, or maybe even a fleet of spacecraft to nudge it a little bit. Not much, just a few millimeters per second. That’s enough, over a decade or more, to cause it to miss.

One way to nudge it is the old tried and true method of the movies—nuke it! But nuke it very carefully! You just want to get it moving, not blast it to smithereens. Some asteroids turn out to be rubble piles of rocks barely held together by weak gravity. If you’re not careful, you could turn what would have been a rifle shot into a shotgun blast and be worse off than before. Nuke it, but a little distance away so that it vaporizes some of the surface rather than blasting it apart, and the reaction drives it in the opposite direction.

If it’s smaller, say around 100 meters wide like the Tunguska asteroid of 1908 that leveled most of a thousand square miles of Siberian forest, we might do with a little less warning time to mount a mission with nuclear devices, or we could do other things if we had more time, like hit it with a massive spacecraft going as fast as we could make it go. That would be like the Deep Impact spacecraft that we deliberately drove into Comet Tempel 1 in 2005. You might need to hit it with more than one to get it moving enough.

If it were still smaller—like the 20 meter asteroid that exploded over Chelyabinsk, Russia last year (generating an explosion 25 times the Hiroshima atomic bomb)—and we had plenty of time, there are other methods like zapping it with lasers from a fleet of spacecraft to vaporize surface material and depend on the reaction to nudge it. Or we could even hover a spacecraft nearby and use the mutual gravitational attraction to pull it, like a gravity tractor but a very weak one.

If you want more information about asteroids, I suggest Googling names like “Asteroid impact” or “Asteroid deflection,” or going to Wikipedia for the same topics. There’s also the NASA Near Earth Object Program web site at that has great detail on potentially hazardous asteroids, but maybe too technical for some.


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