More Things Asteroidal

Here’s more about asteroids, to entertain or scare you.

Is it possible for an asteroid to sneak up on us so that we don’t see it coming?

That’s exactly what happened with the Chelyabinsk asteroid (20 meters wide, 25 Hiroshima’s explosive force) last year that exploded over the Russian city of that name. It came from the direction of the sun, meaning that it approached on the daytime side of Earth and couldn’t be seen until it arrived with a great deal of fanfare.

That’s what the much bigger asteroid in my story does also; it comes out of the sun. There’s an asteroid named Toutatis, about the same size, that did the same thing in 1989. Nobody saw it coming until it had already gone by and passed into Earth’s night sky. It wasn’t particularly close, but the point is that if it had been on an impact course, we would have been blind-sided.

Who decides whether an asteroid is a threat or not?

There’s a NASA program called the Near Earth Object Program at the Jet Propulsion Laboratory (JPL). They were down the hall from me when I worked there. They collect data from astronomers all over the world and compute orbits and impact probabilities. If they find an asteroid with a possible risk, they compare their results with an independent organization in Italy. If they both agree, then they put it on a list named the SENTRY list on their public web site, neo.jpl.nasa.gov. They have dozens of asteroids on that list, but the risks are mostly way out in the future, and they’re very small. Almost all the asteroids on the list eventually drop off it, but new ones are continually being added.

If a bad threat were discovered, then it would be a political decision what to do about it. Right now there is no existing space defense system; there would have to be an ad hoc effort to mount a spacecraft mission to do something about it.

Am I likely to die from an asteroid impact?

Back in 1997, the setting of the book, the predicted chances of you dying over a lifetime were one in tens of thousands, roughly equivalent to dying in an airline accident. Since then, automated discovery systems have found a lot more NEOs (Near Earth Objects) and eliminated most of them as a threat. Nowadays, the odds being talked about are one in hundreds of thousands, less than getting killed by lightning or shark attack. The Chelyabinsk asteroid last year, plus the close flyby of an even larger asteroid, Duende, on the same day, have got astronomers scratching their heads. Some had predicted that we’d see a Chelyabinsk every 125 years. Now some are talking about every 25 years, so that you might see three of them in a lifetime. Most of those are going to hit unpopulated areas like the ocean, though, so you don’t have to fret too much about them. The bigger ones, the Tunguskas around 100m wide, would be around every 5000 years, but the Chelyabinsk event may change the thinking on that, too. The really big ones, one kilometer and bigger, would occur every million years or so. The thing about those is that they have global effects that kick in “asteroid winter” (like nuclear winter), where so much particulate mater is thrown into the atmosphere that the sun is nearly blotted out, temperatures plummet, crops fail, people starve, civilization breaks down, and there are probably wars of survival. For those size asteroids, billions die, a hundred times more than from just the impact by itself.

So . . . the six mile wide asteroid that wiped out the dinosaurs and paved the way for puny mammals like us to inherit the earth happened 65 million years ago. Are we overdue? To paraphrase Ray Bradbury, Does something wicked this way come?

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