Transterrestrial Musings

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Dodging Cosmic Bullets, Part Deux

My, it's a red-letter day. I'm compelled to disagree with Iain Murray twice in a single day, on two different subjects.

The Professor is worried about asteroids on InstaPundit.Com. I take his point that he's not worried about this particular rock, but Steve Milloy's point on JunkScience.com is important here:

Gasp! Shock, horror! Er... hang on. Doesn't this particular rock cross the orbits of Mars, Earth, Venus and Mercury (twice) every 1,321 days (3.6 Earth years)? And hasn't it been doing so for millions of years? Wow! That was a close call alright...

Mr. Milloy is indulging in a fallacy here, similar to the one of the man who jumps off the building, and calls out as he passes every floor, "Doing fine so far!"

It was a very close call in astronomical terms. And in fact it doesn't "cross the orbits" of those planets with any regularity--space is three dimensional. There is no way to know for how many millions of years that particular object has been avoiding hitting planets (it may be a chunk broken off from a larger one that did, in fact, collide with some planet, such as our own Moon).

Of course we shouldn't lie awake now sweating over the fear that this particular object will hit us the next time around the carousel. The point is that it's a reminder that many such objects are out there, some of them have our number on them eventually (as evidenced by past extinctions, and the cratered surface of the Moon, which didn't get that way from too many sweets during adolescence), and that now that we have a civilization worth saving, and the technical means to save it, we should be thinking about it and devoting appropriate resources toward that end.

Of course we must colonize whatever worlds we can, but at the moment that's beyond us. So let's just keep on with our lives until we have the technology. Until then it's best for us to treat this as the interplanetary equivalent of crossing the road. Look both ways, don't build a bridge.

I'm not sure what Iain's point is here. It is not, in fact, beyond us to colonize other worlds now--we simply choose not to. Will it be more affordable in the future? Of course. But that rationale can also be used to put off forever the decision to buy a new computer.

When he says, "just keep on with our lives until we have the technology," one might infer from that that acquiring this magical "technology" is a passive act, like receiving manna from heaven, or cargo from the airplanes and control towers built from palm fronds. Technology is something that we develop (active voice), in response to some perceived need. Glenn and I point this little event out as a reminder that there might be reasons to develop space technology sooner rather than later.

How much we should devote to such an endeavor depends on the expected value of it (i.e., the probability of a catastrophic extraterrestrial event times the cost of it should it occur). I haven't done that computation, partly because I don't know the probabilities (because we aren't even spending the trivial amounts necessary to adequately fund the sky surveys to gather the data with which to do so). But it's certainly not zero, which is approximately how much we're currently spending on it.

And as for "...Look both ways, don't build a bridge," I have no idea what this means in the context of the discussion. The point of the article was that even if we "look both ways" (right now, as I said, we are barely looking at all) we currently have no policy options if we see the car is bearing down on us--bridges are entirely beside the point.

[Update at 10 PM PST]

A reader who calls him/herself "skeptic" asks:

What is the probability and how was it calculated? If it is based on known events and conditions, that is fine. But what is it?

As I pointed out, we don't know, because we haven't even spent the money needed to gather the data necessary to do the calculation. The known events are many (e.g., in 1910 a meteor or comet known as the "Tonguska Event" hit a remote region of Siberia. Had it occurred in a populated area today, it would have caused billions of dollars in damage, and thousands, perhaps millions, of lives).

If it is based on what we don't know, that is *not* fine. I don?t care what it is; it is speculation.

So we should ignore it if it's based on willful ignorance?

What can we do about it? It would take a massive, massive amount of energy to alter the orbit of anything substantial.

Do you have some calculations to back up this claim? In fact, the amount of energy required to divert an object from its path sufficiently to prevent a collision with earth is quite small.

Hydrogen Bombs would be insignificant.

Ummm... no. Do you have any idea whatsoever what you're talking about?

Even if we could amass the required energy, how would it be delivered?

By landing a small probe on the body, setting up a solar-powered or nuclear de-vice that could utilize its own mass as a rocket to divert it the few meters per second that would be required to prevent the catastrophe.

I am all in favor of space exploration. But I am not big on tax-funded research: who gets to set priorities? Politicians ? I hope not. Speculators ? I hope not. Scientists - How do we choose?

I said nothing about tax-funded research. Presumably we would choose based on who would do the best job of providing results.

Posted by Rand Simberg at January 08, 2002 05:33 PM

Comments

Funny about those astronomical terms: whole galaxies can die out in the blink of an astronomical term. The guy falling off the building can die of old age long before his lifeless body hits the ground.

What we don't know, we don't know. And it really is silly to get concerned about what "might" be "out there" that we don't know about.

Posted by skeptic at January 8, 2002 08:10 PM

Only if the probability is improbably low, and there is nothing that we can do about it. Neither condition applies in this case.

Posted by Rand Simberg at January 8, 2002 08:44 PM

What is the probability and how was it calculated?

If it is based on known events and conditions, that is fine. But what is it?

If it is based on what we don't know, that is *not* fine. I don?t care what it is; it is speculation.

What can we do about it? It would take a massive, massive amount of energy to alter the orbit of anything substantial. Hydrogen Bombs would be insignificant.

Even if we could amass the required energy, how would it be delivered?

I am all in favor of space exploration. But I am not big on tax-funded research: who gets to set priorities? Politicians ? I hope not. Speculators ? I hope not. Scientists - How do we choose?

Posted by skeptic at January 8, 2002 09:52 PM

G'day Rand,

A chap over at Techcentral puts a good case for the US Dept of Defense to be involved in asteriod

defense, see:

http://www.techcentralstation.com/1051/defensewrapper.jsp?PID=1051-350&CID=1051-123101A

Giving NASA some competition would be useful.

Posted by Ralph Buttigieg at January 9, 2002 12:00 PM

The questions that skeptic poses are good ones. Aside from Tunguska, and the dino-killer, what other objects, and over what size and time scale, have struck the earth. This question should be answerable without a space survey, and must be answered to determine what type of space survey should be done.

On another note, defense against an inbound object is CLEARLY the DoD's job, and regardless of the difficulty, they should be doing it. At the very least, they should have a plan for dealing with objects within the plausible range, over the plausible time frames for discovery and response. This plan should be unclassified, at least to the extent that it does not overlap with military (non-asteroid) operations. I don't think comets and asteroids read position papers, so I think that we can safely disclose the information!

Based on the information at my disposal, I can do a simple calculation. A known event occurred in 1910, with little effect on human civilization. Two possibilities exist; 1) Impacts are rare on the timescale of human civilization, and therefore are not a concern, or 2) Impacts are frequent on that timescale, but so far have never occured in an area populated by people capable of recordkeeping, and physical evidence is difficult to analyze. As I said before, this should be answerable, and any information on the answers would be appreciated.

Posted by Paul Orwin at January 9, 2002 12:24 PM

They are many, and probably many more than we are aware of, because geological processes eventually obliterate the results. As I said previously, if you want to get an idea of how many objects strike the earth, look at the Moon. We are larger than the moon, and represent both a bigger target, and a bigger gravitational "vacuum" sucking in many more objects. The earth isn't cratered like the Moon because the evidence is being continually eroded away by water and air.

As another example, look at the Meteor Crater outside of Winslow, Arizona. It's a mile in diameter, happened within the past several thousand years, and likely killed off all life within a couple hundred miles when it hit. Some of the Biblical catastrophes may have been actual historical impact events. That Tonguska happened within the past century should be disquieting. The amount of money required to do a sky survey is trivial, even compared to NASA's current budget.

As for your comment about the DoD, see today's post.

Posted by Rand Simberg at January 9, 2002 12:33 PM

I agree with Paul Orwin. We dont need an extensive space survey to determine hits on earth.

It is way too much of a stretch for me to accept the claim that there may be more examples than what we know about; it is just that the evidence for them is no longer available. We can say the same about the existence of unicorns: there are more unicorns than we know about (none). We just don?t have any evidence for them. Maybe the elves ate it. Er, sorry, the evidence for the existence of elves is not currently available?

Rand: Some responses (***)to your responses to my earlier comments. You have made me think about this stuff again. Thank you for that.

*** ?So we should ignore it if it's based on willful ignorance? is this something like saying ?As I pointed out, we don?t know? and proceeding anyway? Maybe we could find out first and see if it is real problem. (We could do this without a space survey.) Lots of scientists don?t think it is a problem: it really would be willful ignorance to ignore them.

Hydrogen Bombs would be insignificant.

Ummm... no. Do you have any idea whatsoever what you're talking about?

*** A number of scientists who work or have worked with nuclear weapons have stated this. I have heard Dr. Bill Wattenburg make this statement on a number of occasions. He has worked extensively with nuclear weaponry.

By landing a small probe on the body, setting up a solar-powered or nuclear device that could utilize its own mass as a rocket to divert it the few meters per second that would be required to prevent the catastrophe.

*** This is a nice theory. ?Do you have some calculations to back up this claim?? From what Dr Bill and others have said it would have to be a pretty small body to have its trajectory altered by a bomb. Also, I just finished reading an article that said space debris often have relatively dynamic trajectories. If it does not have a static path how do we know we changed it? If it is dynamic, it any miss anyway.

I said nothing about tax-funded research. Presumably we would choose based on who would do the best job of providing results.

*** I did not suggest you said anything about tax-funded research. I was making a general point about scientific funding, based on some personal experience: A number of years ago I worked as a computer programmer with a group of oceanographers, meteorologists, and physicists. It was a government-run tax-payer funded effort. You can rest assured the only research and projects undertaken were approved by the politicians. They had their own idea of providing results ? getting re-elected. Scientific merit did not really enter their funding determinations. They most often could not make an informed decision about science. But they knew a lot about getting votes.

Posted by skeptic at January 9, 2002 10:01 PM

Actually, I think the Moon is a terribly misleading indicator, for the very obvious reason that it has no atmosphere. Because of that, any object on a trajectory that intersects it (in space and time, of course) creates an impact crater of predictable size. Earth's atmosphere, with the attendant "frictional" force, burns up many (most?) objects on an impact course, and reduces the size of objects too large to burn completely. You are correct about the erosive effect of geological and hydrological processes, but I still think that a talented and dedicated geologist could use methods such as heavy isotope detection and rare element detection as well as physical craters to quantify the rate of impacts globally (at least terrestrial ones; we will have to infer the rate of sea impacts from that) I am not saying that it is an easy thing to do, just that it is likely to be easier, cheaper and more relevant than a near space survey.

Posted by Paul Orwin at January 10, 2002 12:26 PM

>Actually, I think the Moon is a terribly misleading indicator, for

>the very obvious reason that it has no atmosphere. Because of

>that, any object on a trajectory that intersects it (in space and

>time, of course) creates an impact crater of predictable size.

Yes, but this only explains the fractal nature of craters (many microcraters as well as large ones). It doesn't explain the large number of large ones.

>Earth's atmosphere, with the attendant "frictional" force, burns

>up many (most?) objects on an impact course, and reduces the size

>of objects too large to burn completely.

Yes, it burns up most objects (we saw a spectacular example of that in the Leonid Showers in November), but the ones that it burns up are small--they're not the ones of concern here. It does not burn up 300-meter objects, nor does it even significantly diminish them. These are killers.

You are correct about the erosive effect of geological and

>hydrological processes, but I still think that a talented and

>dedicated geologist could use methods such as heavy isotope

>detection and rare element detection as well as physical

>craters to quantify the rate of impacts globally (at least

>terrestrial ones; we will have to infer the rate of sea impacts from

>that) I am not saying that it is an easy thing to do, just that it

>is likely to be easier, cheaper and more relevant than a near space survey.

Nope. Doing a space survey is cheap, and reliable. We don't have to expend lots of resources trying to infer things--we can determine them directly. We already have enough data to know that it's a danger. What we don't have is specific data on which ones constitute the most danger.

You want to spend geologists' time and money (as well as the cost of the instrumentation) to answer a question that is already answered--asteroids are a potential danger. Now it's time to do a sky survey, which with the new adaptive optics telescopes, ever-cheaper computers, and the use of Arecibo, can be done for a relatively paltry amount (compared with, say NASA's existing budget). This will allow us to not only assess the risk, but to provide information needed to come up with plans to mitigate it.

I really don't understand this reluctance to believe that asteroids are dangerous. Are you one of the people who didn't want to believe Alvarez' theory about the Cretaceous extinction? Most of the resistance in the scientific community to that looked religious to me (i.e., how can anything not of this earth have such a dramatic terrestrial impact?)

Posted by Rand Simberg at January 10, 2002 01:06 PM

As usual, Rand has many good insights, and a penchant for the type of argument that keeps me from my work (as well as my blog!), but the # of large craters on the Moon is also explained by lack of atmosphere, albeit indirectly. Without an atmosphere, no liquid water can last, therefore no flow of water/vapor into a climate cycle, therefore little or no erosive destruction of cratering. I have never done the math, but it seems to me that a few billion years is plenty of time to cover a relatively small surface with impact marks if none of them ever disappear. I stand by the comment that the Moon is a poor proxy. As for the greater question of what the best practical surveillance method is, I am not in a position to argue the expenses of the space survey (although the track record of NASA is not very good, as I am sure you will agree), but the geological survey would not only utilize instrumentation readily available, but could probably be done using data that has already been analyzed and described, just not for this purpose. Since geology budgets are orders of magnitude smaller than the astronomical (!!!) budgets of space projects, I think it should be at least considered. (A disclaimer; I am neither an astrophysicist or a geologist, and therefore not qualified to comment on any of this at all!)

Posted by Paul Orwin at January 10, 2002 03:31 PM

>...the # of large craters on the Moon is also explained by lack of atmosphere, albeit indirectly. Without an atmosphere, no liquid water can last, therefore no flow of water/vapor into a climate cycle, therefore little or no erosive destruction of cratering.

Of course. I already said that. My point is that the number of (large) craters on the Moon is indicative of how many large objects have hit it. The number of similarly large objects to hit the earth is greater by two factors: 1) the much greater target area of the earth's surface, and 2) the much deeper gravity well of the earth, which sweeps many more such bodies into its influence. The only reason that we don't see even greater impact evidence on earth is precisely because we have an atmosphere (not because it keeps them from coming in--it doesn't, except for the sandlike particles that comprise most meteors, but because the surface of the planet is so dynamic, and destroys most of the evidence).

Again, I'm amazed that you don't take seriously the fact that we had a potentially catastrophic event within the past one hundred years at Tonguska. Either that was an extraordinary (almost inconceivably improbable) coincidence, or such events are much more common that some of us would like to believe. This, combined with the visible lunar evidence, seems utterly compelling to me, and most people who have actually studied the issue.

>I have never done the math, but it seems to me that a few billion

>years is plenty of time to cover a relatively small surface with

>impact marks if none of them ever disappear.

It is plenty of time, but there are also plenty of craters, many of them more recent than others. In fact, most of the visible craters are relatively recent, because they've covered the ancient ones. The crater Tycho was created in historical times--medievil monks reported a "fire on the Moon" in the region that corresponds to it.

>I stand by the comment that the Moon is a poor proxy.

It is the canary in the coal mine. The earth has been bombarded much more heavily.

>As for the greater question of what the best practical

>surveillance method is, I am not in a position to argue the expenses >of the space survey (although the track record of NASA is not very >good, as I am sure you will agree),

Yes, I would agree, but NASA doesn't do such things--astronomers do. No "space projects" are needed.

>but the geological survey would not only utilize instrumentation

>readily available, but could probably be done using data that

>has already been analyzed and described, just not for this purpose.

And as I said, it has already been done to the satisfaction of those actually working the field. Now it's time to gather the useful data.

>Since geology budgets are orders of magnitude smaller than the

>astronomical (!!!) budgets of space projects,

As I said, this is not a "space project," in the astronomically-large budget sense. Actually doing something about it would be, but that, as I said, should be a job for an agency other than NASA.

Posted by Rand Simberg at January 10, 2002 04:34 PM

And one follow up to skeptic:

>>Hydrogen Bombs would be insignificant.

>Ummm... no. Do you have any idea whatsoever what you're talking about?

But nuclear weapons specialists don't necessarily know anything about moving asteroids. If he was saying that bombs are very inefficient, and a dumb way of diverting asteroids, then I agree completely. But that doesn't mean that amounts of energy larger than nukes are required.

>By landing a small probe on the body, setting up a solar-powered or nuclear device that could utilize its own mass as a rocket to divert it the few meters per second that would be required to prevent the catastrophe.

*** This is a nice theory. ?Do you have some calculations to back up this claim??

I'd have to go dig out the references, but it has been studied extensively.

>From what Dr Bill and others have said it would have to be a pretty

>small body to have its trajectory altered by a bomb.

As I said, no one sensible would use a bomb. It makes for nice Bruce Willis movies, but has nothing to do with the reality of moving planetary objects in a predictable and effective manner. Bombs just turn one large asteroid into a bunch of small ones with the same trajectory.

>Also, I just finished reading an article that said space debris

>often have relatively dynamic trajectories.

They don't "often" have dynamic trajectories--they always do, due to solar and other perturbations. But that doesn't mean that we can't predict their motion for short (months/years) periods of time.

>If it does not have a static path how do we know we changed it? If it

>is dynamic, it any miss anyway.

Assuming that you mean that it "might" miss anyway, we will know that we changed it the same way we know that it's a danger. By taking measurements of its trajectory, and propagating it in a computer simulation. This can be done to a high degree of confidence for short (in astronomical terms) but long (in human terms) periods of time. If we couldn't do this, we wouldn't be able to put a probe in a precise orbit around a moon of Jupiter, or make course corrections to it, something JPL does routinely.

Posted by Rand Simberg at January 10, 2002 05:21 PM

I never said that I don't take the threat seriously, nor that I don't think it should be addressed, only that I would like some harder data estimates based on known data from historical record or easily obtained geological data. Your comments on Moon craters are enlightening to me (I really know next to nothing about lunar geography/geology). I am not trying to imply that Tonguska is a rare coincidence, either, just asking about any hard data on impact frequency. The evidence that we should think and act on these things is compelling, I agree. I think some healthy skepticism on the magnitude and direction of the response, however, is, well, healthy. As far as the nature of the survey, if it is so cheap, and everyone who thinks about it is in agreement that it should be done, then what's the problem? I would submit that tracking objects of the size of planet-killer asteroids/meteors (1-10 km radius?? pretty small, anyway) is difficult from earth bound 'scopes. Anyway, I am really just playing Devil's advocate now, so maybe I will just let it lie for now. Thanks for the informative discussion, all.

Posted by Paul Orwin at January 10, 2002 05:33 PM

Well, when I say cheap, I mean as government programs go. It's still rather expensive as private activities go (though there is a non-profit organization called The Watch, at http://www.space-frontier.org/PROJECTS/THE_WATCH/, that is trying to do that). And while people who've been studying it have reached a consensus, that's not the same thing as getting politicians and/or philanthropists to go along.

Earth-based telescopes are perfectly adequate to the job, particularly the newest ones with adaptive optics. Space-based telescopes could do better, but we can start the job without them.

Posted by Rand Simberg at January 10, 2002 06:02 PM

Rand: I am very interested in the calculations, including how the energy is to be amassed and deployed. A URL would do it, if you have one.

I would also appreciate more on the ?missing evidence? of previous hits. I really do see this as being similar to ?missing evidence? for unicorns.

In this regard, is the rate and movement of space debris constant over many millions of years? Is it still happening at the same rate as it did eons ago? Is the moon still under going major bombardment?

FYI: Dr Bill is not just a weapons expert. His comments on nuclear bombs as tools were that they do not release enough energy to be of use, not that they would blow up the objects. As I recall, he said objects large enough to have an impact on earth would just not be affected by a bomb blast.

Dr Bill has done a lot of neat things in a number of areas. He currently has a very reasonable scheme for clearing land mines that does not endanger anyone. You can read about this and some of his other exploits at http://pushback.com.

Posted by skeptic at January 10, 2002 10:04 PM

>I am very interested in the calculations, including how the

>energy is to be amassed and deployed. A URL would do it, if you have one.

I don't, and don't know if it is available in non-dead-tree form, but there was quite a bit of work done on this in the Princeton Conferences on Space Industrialization (though the application there was to move asteroids for the purpose of mining them, rather than simply preventing collisions).

Also, the calculations depend on the size of the object, how far it is from the planet, how much margin you want to ensure in the new trajectory, its precise orbital parameters, etc.

>I would also appreciate more on the ?missing evidence? of previous

>hits. I really do see this as being similar to ?missing evidence?

>for unicorns.

I don't know how you can make such a comparison. You're comparing something for which there is no evidence at all (unicorns) to something for which there is abundant evidence, and the only issue in dispute is the quantity.

>In this regard, is the rate and movement of space debris constant

>over many millions of years? Is it still happening at the same rate as it did eons ago?

Pretty much.

>Is the moon still under going major bombardment?

Of course.

[Update]

Strike those last two comments, or amend them. Too early in the morning.

The collision rate was much greater when the solar system was young, of course, and all the planetary impacts did clean things up quite a bit. I thought that you meant in the last few million years, over which the rate has been fairly constant. Hundreds of thousands of objects still remain, however, many in earth-crossing trajectories (the so-called Apollo-Amor class).

I should also note, in fairness, that I accidentally misinformed Paul on a related subject. It was not the crater Tycho that was caused by a medieval impact viewed by monks--it was the Giordano Bruno crater. And a recent finding, of which I was unaware, indicates that this theory has been discredited (only in the past year). The new theory is that what the monks saw was a meteor approaching them between the earth and the Moon.

So the case may not be as strong as I've previously made it, but it remains strong enough to keep an eye out, since the cost of doing so is relatively trivial.

>FYI: Dr Bill is not just a weapons expert. His comments on nuclear

>bombs as tools were that they do not release enough energy to be of

>use, not that they would blow up the objects.

Whether or not they blow up the objects, I don't necessarily disagree with the statement above. It is not the same as the statement that they don't contain enough energy to move an asteroid--they do. The point is that the energy released in a nuclear explosion is not an effective way to move celestial objects.

>As I recall, he said objects large enough to have an impact on earth

>would just not be affected by a bomb blast.

And he is right. That's why you don't do it with a bomb blast. You do it with rockets.

Posted by Rand Simberg at January 11, 2002 08:17 AM

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