Category Archives: Asteroids

Still More Things Asteroidal


A 20 meter wide asteroid exploded over Chelyabinsk, Russia last year and got the world’s attention with a 500 kiloton explosion equivalent to 25 Hiroshima atomic bombs. Seven thousand buildings were damaged and 1500 people were injured, most of them by flying glass. The asteroid was not known beforehand because it approached from the direction of the sun—on the Earth’s day side where it couldn’t be seen. Fortunately it exploded at high altitude, almost 30 kilometers up, so that a lot of the energy was absorbed by the atmosphere. (The resulting pressure wave circled the Earth more than once.) This helps account for the fact that no one was killed. Another thing that reduced the damage was the shallow approach of the trajectory: the asteroid almost skimmed the atmosphere. If it had come in close to vertically over the city, there likely would have been much more damage and many casualties.

Recently (2014/09/07), another Chelyabinsk sized asteroid (a little smaller, 13 meters wide) skimmed by Earth on a trajectory just outside our geosynchronous satellite orbits. In the astronomy world of asteroid encounters, this was an incredibly close call. Unlike the Chelyabinsk asteroid, this one was found a few days before the event because it approached from the opposite direction—opposite the sun, on the night side of Earth. However, if it had been on a predicted impact course over a populated area, a few days lead time would be insufficient to do much more than alert the population and perhaps evacuate the area. Fortunately, most impacts like this would be over unpopulated regions like the ocean.

NASA estimated in 2012 that there are 4,700 potentially hazardous asteroids larger than 100 meters that could pose a danger to Earth. About 70% of these hadn’t even been discovered. However, we (our world-wide astronomical community and NASA in particular) seem to have pretty good automated discovery programs going that chip away at that percentage pretty fast. NASA set a goal in 2008 of discovering 90% of potential threats over 140 meters, and that may happen by 2020, leaving us with only 10% to worry about.

Some of the discovery programs are the Catalina Survey near Tucson, Arizona and the Pan STARR program on Mt. Haleakala in Hawaii. Then there’s the Atlas program, also Hawaii, funded by NASA, starting up next year with two telescopes covering the entire sky several times every night. After that, there’s the B612 Foundation, a private organization partnering with NASA and others; they plan to launch an infrared satellite named Sentinel by 2018 and put it into a Venus-like orbit inside Earth’s orbit so it can find objects in regions poorly seen from Earth.

The main thing we’re lacking, though, is an asteroid defense system. We’re studying ideas about how to deflect dangerous asteroids, but we don’t know whether any of these things would work because we haven’t tested them in space. If we want to be proactive and get ready for a low probability event that could have massive consequences, we’d have to actually build some spacecraft and send them out to asteroids and try out some of these methods.

That would cost a lot of money. Taxpayer money. That would require political decisions. These are things that are in short supply in today’s political climate.

So there’s the question: We’re willing to spend lots of collective money on low probability events like winning a lottery; we spend a lot of money keeping the odds of airline accidents low; are we willing to spend some money on keeping the world safe from asteroids? Or do we say “Don’t fix it if it ain’t broke,” or “Let sleeping dogs lie,” or “Never worry about a disaster until after it happens,” or some of those other non-proactive things?

What do we do about it? That’s the question The Darkest Side of Saturn asks and answers in an alternate universe. That’s probably the question we ought to answer in our particular universe.


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, 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?


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.