Exploring abrupt climate change induced by comets and asteroids during human history

New Study: Impact frequency on Jupiter wrong by order of magnitude

More proof the emperor is buck naked from Physics ArXiv Blog:

Tuesday, May 18, 2010

The strike on Jupiter last year raises the likelihood of future impacts by an order of magnitude, says a new study. But what does it mean for the Earth?

Last July, an amateur astronomer noticed that a mysterious dark bruise about the size of the Earth had suddenly appeared on the surface of Jupiter. Within hours, amateurs and professionals alike were training their instruments on the great planet to work out what had happened.

The consensus was that Jupiter had been hit by a comet or asteroid. But the surprise was that it had happened so soon after the Shoemaker-Levy comet strike observed in 1994. The worry was that this strike must have important implications for the likelihood of future impacts.

Today, Agustin Sánchez-Lavega from the University of the Basque Country in Bilbao and pals, publish their analysis of the impact and how it changes the probabilities of future impacts. They say the impactor was probably an icy object about 1 kilometre in diameter which came either from a group of main belt asteroids called Hilda asteroids or from a group of comets called the Jupiter Family.

Estimating the likelihood of such impacts is hard for a gas giant like Jupiter because the events leave no long-lasting scars on the surface. Jupiter’s bruise has already faded away.

So astronomers have to rely on historical records. Before last year’s impact, astronomers knew only of the Shoemaker-Levy impact and a possible impact observed by the Italian astronomer Giovanni Cassini in 1640. Together with other evidence such as crater counts on Jupiter’s large moons and various theoretical calculations, astronomers guessed that Jupiter was liable to a strike perhaps as rarely as once in every 350 years.

Sánchez-Lavega and co say that last year’s strike significantly changes these numbers. Seeing two strikes in 15 years means that that Jupiter may be liable to be hit as often as once a decade. The reason we haven’t seen impacts before is simple: digital cameras and image processing techniques have only become easily available to amateurs in the last ten years. (Before that, even professionals often had to rely on hand drawn pictures of the planets.)

What Sánchez-Lavega and co do not address are the implications for the likelihood of Earth impacts, which is strange given the huge importance and public interest in such an event. The Shoemaker-Levy impact on Jupiter changed the way astronomers think about possible impacts and generated huge interest.

Clearly Jupiter is at greater threat of future impacts than Earth: it is bigger and more massive by far and so is bound to attract more hits. But it can also send bodies our way.

The current thinking is that a 1-kilometer object ought to hit Earth every 500,000 years or so. Needless to say, such an event would change our civilisation beyond recognition.

If last year’s impact on Jupiter increased the probability of another strike by an order of magnitude, by how much does it increases the probability of a strike on Earth? The public deserves an answer to this question and the fact that this team are silent on the matter is worrying.

Let’s hope Sánchez-Lavega and his colleagues are working on an answer as a matter of urgency.

32 Responses

  1. Although this latest impact on Jupiter was much smaller than the Shoemaker-Levy 9 (about one twentieth the size), I find it peculiar that compared to the 1994 the recent impact received so little media attention.

  2. It’s just as well for us that Jupiter is there, because the planet is acting as a kind of giant vacuum cleaner, sucking in asteroids and comets which might otherwise hit us.

  3. A few things come to mind here…

    Once again, science shows that what has been “known” as fact – in this case the frequency of impacts on Jupiter – turns out to not be fact at all, but just some calculations based on some assumptions, assumptions that turn out wrong. Science is a sequence, a continuum, and we are always at some intermediate point on that continuum, meaning real facts are often somewhere out there in the future, no matter how certain we are that today’s understanding is correct… It is amazing how often scientists say, “Wow, we have to throw out what we thought we knew and incorporate this new information.” And that is what it is about – having concepts that work for a while and then replacing them as we learn more.

    Photos of Jupiter go back only 100 years ago, tops, and the ones older than 30 years probably aren’t worth a hill of beans for spotting anything on Jupiter. The rings of Jupiter weren’t even found until 1979. I remember being amazed when they found them, because I literally had a dream at the end of 1973 in which I saw Jupiter with rings. (It was a pretty cool dream, all in all. I still remember most of it.) It didn’t mean anything, but it gave me goose bumps anyway.

    I wouldn’t give much chance for any clear photos older than Voyager in 1979 – but they MAY be out there. In the first few decades of seeing Jupiter would anyone have even been looking at changes? The top of the atmosphere is always changing and the early viewers may have thought now features were just storms. It would be worth a look see, if anyone has the inclination.

    I think SL-9 did more than make people think about impacts. I think it opened up the entire catastrophe issue for discussion. That may sound like splitting hairs, but as I see it catastrophism has been more about the past, while impacts seems to have more focus on the future – Ed’s book being at least one notable exception. It is the difference between looking for NEOs and looking into old accounts from indigenous peoples.

    I had always thought that the markings on Jupiter were impermanent, except the Great Red spot and a few other major ones. Is there any chance at all that this was just an atmospheric effect?

  4. Don’t get confused between uniformity and uniformitarianism! With the lack of a lengthy record of impact data for any body in the solar system, we should not attempt to draw too many inferences from this. Especially if you have to start looking at moon crater density and then attempting to calculate long-term impact frequency. That is uniformitarian thinking to the core. It is clear from examining our own moon that lunar impact rates have been anything but uniform over time.

    The question is this, how much of our international resources should be expended to protect the earth against a comet or asteroid impact? We haven’t had one documented in historical times by those keeping records. And does anyone really think we have the technology to deflect something the size of an object that, say for argument purposes, created Davias’s Saginaw Bay event? How does that eventuality stack up against the real-time humanitarian needs all over the world?

    These discussions are all very interesting and academic, but the reality is that for all but the smallest rocks, a “Space Guard”-type monitoring system is going to do nothing more than give us a much longer awareness of the impending impact. More time for panic and general chaos. Something that could affect millions or billions of people simply can’t be prepared for.

    Sorry to rain on your collective parade, but I’m just not as fired up about this as some of you are.

  5. Terry –

    I am with you, about the unlikely possibility of protecting us against big honker NEOs. Mostly I haven’t heard any plans that I think will work against those. But I think some plan will work. Just one we haven’t thought of yet. So I don’t think it is all just acameic – I just think we’ve chosen poor options, ones that aren’t likely to work reliably enough.

    Defining the problem and brain-storming solutions, on my own wish list for ways of protecting us against the largest possible incoming comet or asteroid, would be at least one “launch bay” on Mars and a launching space station at each of its Trojan points. There is a need to have at least two launch points, because Mars may not be on the good side of the Sun when we need to interdict something. I’d want the launch bays as far out as possible, so that we can divert as early as possible. A little bit of nudge early is worth a lot of nudge later.

    As choices to study we’d have two options of direction, and two options for duration of intervention.

    For direction I favor just pushing the object up and out of the plain of the Earth, because once it is on a skewed orbit we would likely never have to deal with the object again. I may be wrong on that being possible on the incoming path. The other directional option is to kick it to one side or the other.

    For duration we would have either a short abrupt kick or a long sustained milder kick. With either duration we’d want to impart the maximum amount of energy for diverting it; milder does not mean less, just slower. A steady side thrust would give us a nice diversion at least cost, I think, because we wouldn’t need. But a steady mild thrust must happen early; going out from Earth is too late for this one. Early is better with nukes, too. I’d do a mirv approach with the warheads exploding sequentially along the path – complicated but easily possible with computerization, accelerometers and good old gyroscopes.

    A third option factor to consider is to slow the NEO down or speed it up, so that its Earth orbit intersection changes in time.

    I don’t think the present way – rockets from Earth – are adequate for either the early-bird-getting-the-worm reason, but also with a head-on fly-by timing is everything and we only get one shot at it. If our rockets are traveling in the same direction the relative speeds are not additive but subtractive, so we would have a longer time next to or behind or in front of the NEO. A longer time means if something glitches there would be time to implement a ‘Plan B’.

    No pun intended, but this logic isn’t rocket science. Putting the rocket in position IS rocket science, but framing the problem isn’t.

    Pulverizing the NEO isn’t an option, unless it turns the NEO to baseballs without leaving large remnants.

    As to panic, what difference does it make if we panic or not, if humanity is being wiped out? No matter what the religious sorts think, our demeanor doesn’t make a damned bit of difference.

  6. Steve, as you said, it’s all physics. But the physics involved in intercepting a very fast object, and matching speeds with it to land a thruster on it if we are going to use your milder method, involves powerful launch and orbital maneuvering vehicles that are still decades or even centuries in the future. And your other plans, a Mars interdiction base and Lagrange orbital stations, are stuff of science fiction, considering the state of the world economy. No one has those kinds of resources nor will they for the foreseeable future.

    The optimal situation would be detecting an NEO and computing a potential terrestrial impact that was many years into the future. Then there would be enough time to develop a plan for that specific instance. But to expect the world’s nations to fund an ongoing defensive rampart “just in case” is unlikely. The effort and interest would last probably no more than a generation or two. And then new regimes would pull out to address more pressing issues here on earth. Our life spans are just too short to be concerned about something like this. Now a near miss might change that, but even then, I would give our response only a hundred years or so before we get distracted with more mundane things and the defense system falls into disuse.

    I guess my view of the endgame is different than yours. It’s true that after the fact, it wouldn’t matter if we were terrorized and in chaos for a month or a day before being wiped out. But my humane side would hope for the shorter period. Interestingly, Revelations 8:10 clearly describes a meteorite or comet falling to earth and polluting a third of the waters of the earth. Many people (a third of the world’s population?) died as a result. So I am more convinced than probably most that there will be an impact in the future. But humanity will be dealing with other even more serious issues at that time. Like the supernatural end of the world.

  7. @Pierson Barretto: The fact is that many survived. We’re here, right?

    Excellent point! It’s like I always say about the Cold War: The Russians were supposed to be so good at everything: Sputnik, espionage, missiles, AK47, MIG27. BUT WE WON, RIGHT?

  8. Hi Hermann

    Yes, it can be! So if you think it is! But there is controversy. Sorry, I’m not so sure. As I always say: with one eye only, it is not possible to have a good perspective of the facts. On the land of the blinds, who has one eye is king, but the king is one-eyed!!!

    Away from politics, and back into focus: what do you think of blowing up a comet, it would be better than let it fall entirely in one point?


  9. You can get hit fifty times with fifty pounds of force and survive the beating. You may be bruised, and battered. But you’ll stand a good chance of making a full recovery. But if all of that force hits you at once, in one blow of 2500 pounds, that’ll be the end of you.

    If comets like Linear, or SW-3, are any indicator of typical structural integrity of a comet, they may be too fragile to turn aside, or deflect. Possible mitigation, or preparation, for an impact may be limited to civil defense. There is a good chance that we won’t be able to do anything about it but hide in holes, and caves.

  10. Hi Pierson: Blow up a comet and turn it into a myriad of meteoroids..

    It’s certainly worth a try! ?;^) [<– 2 eyes!]

  11. But, assuming it would take a nuclear explosion to fragment it, wouldn’t the myriad of meteoroids be radioactive?

  12. The Deep Impact mission to comet TEMPEL 1 showed the head of that comet to have the consistency of a dirty snow bank. It also showed that the object is a geologically active body. Comet HOLMES is unstable, and prone to violent outbursts.  Comet LINEAR , and Comet Scwassmann-Wachmann 3, make it abundantly clear that total, explosive, fragmentation of a comet can occur spontaneously at any time.

    In other words, a comet coming at us will probably be a cluster of fragments by the time it gets here. No nukes required. And no way to deflect it.

  13. Hi Barry

    Yes, along with pollution from cyanides, we would have pollution by radioactivity. But I believe it would be less than the radioactivity of the fields of atomic explosions on Pacific, Russia or U.S. Noting that a fusion bomb (not fission) is more potent and less radioactive than a fission bomb. It is questionable how many megatons would be needed to fragment a large comet, with about 50km in diameter? Although it is a low density celestial body.


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  17. Dennis –

    I don’t get your logic on the “fragile” comets. Please explain to me how a fragile comet is less able to be diverted.

    Impact is all about unit stress, technically speaking. From an engineering viewpoint the impact on any square inch being the same, a solid one has more capacity to resist the blast impact, and it is more likely to simply rotate rather than be pushed laterally. If it is less strongly agglomerated, an increased number of pieces will get shredded/sheared off it and take other pieces with them. Less consolidated also means fracture zones or less adhered zones will open up further, and more will break open, letting the pieces be pushed farther.

    How is weaker stronger? Please educate me. I don’t see it.

  18. When did I say that ‘weaker is stronger’? The weaker objects are only more dangerous.

    Lets try a little thought experiment. Imagine you’re standing at home plate, and I throw you a fast pitch. The first pitch you get a good hit. But the next pitch, instead of a hardball, I throw a clump of dirt. You swing, and connect. But this time, insted of going out into the bleachers behind center field, when the bat connects, that clod explodes into a cloud of fragments, and you eat dirt.

    The breakup of comets is already a well recognized route to their destruction anyway. So we can’t assume we will find enough structural integrity to push against, without causing the comet to break into a cloud of fragments. Any attempt to apply enough force to nudge one into a differnt orbital path would be foolhardy without some way to measure the structural integrity of the object first.

    Take a look at images of the breakup of SW-3, or images of the fragmented linear, both typical Taurid family objects, and then tell me how you would deflect a cloud of fragments like that.

  19. F = ma

    If we do the expected nuclear blast on a fragmented comet, the blast wave will be quite effective against fragments. It is not a shotgun with individual pellets. It is a rapid expansion of ENERGY, a full wave front. The blast is not shrapnel that might miss, but a continuous wave front. It is not just Uranium atoms being driven outward, you know. Each cometary particle will be driven nicely to the side. The smaller the fragments are, the better.

    I like the chances with a fragmented comet much more than with a single body. If I had to talk about % effectiveness, I’d say the fragmented with smaller pieces would be a 80%, and a single one I’d put at 30% chance of getting the result we want. And that is just in terms of MOVING the objects.

    ALSO, the effective total force is proportional to the exposed area of the comet – the area facing the blast. If it is a perfect sphere, the area in question is at its smallest (not counting if it is rod shaped and the blast hits it end-on). The only part of F in the equation that matters is the part that impacts some portion of the comet. The smaller the exposed comet area, the more of the blast will go to waste.

    A fragmented comet has MORE area exposed, and thus the effective F force is greater. With an intact comet, particles on the far side do not get impacted, except indirectly. They are, then, mass that must be moved, but which contribute nothing to moving the comet sideways. They are, in fact, dead weight, lowering the acceleration of the comet’s mass. The same particles (however big), if they are fragments, are exposed to the direct effect of the blast. That is a good thing. There is less dead weight to move. More of the comet is exposed to direct impact with the blast wave.

    Less consolidated ones will be MUCH more likely to be pulverized – and THAT would be the best of all outcomes, because then diversion isn’t even necessary, because entering the atmosphere a large amount will simply burn up. Smaller is GOOD.

    With a large single, solid body, there is no guarantee at all what size pieces remain. So if the gods pre-fragment it, great. The closer we can get them to “atmosphere burning”, the better.

    In fact, I would submit that the Dresden approach be used, a two-step process to get maximum effect. At Dresden in FEB 1945, the Brits flew over in the first wave and dropped concussion bombs to open up the buildings. 45 minutes later the Americans dropped incendiary bombs which were much more effective in opened-up buildings than they would have been if dropped normally. So, I suggest that we fly TWO nukes up – a first one to fragment the comet and then another to push the fragments to the side.

    I actually thank you for getting me to think about this. Fragments good, solid comet bad. Or at least less good.

    Your analogy of the dirt clod – ????????? The only danger to a batter is if he gets dirt in his eyes. Our nuke that just blew up is on no way like a batter with dirt hanging in the air. “Eating dirt”? Wow. Sorry, I think you could have come up with a better analogy.

    Thought experiments: When Einstein invented the “thought experiment” he was setting science back 300 years, prior to the advent of the scientific method of rule by empirical experiment which had finally taken a big step in 1660 or so with the formal advent of the Royal Society. Researchers had been working up to that for some time. The Royal Society basically ruled in its charter that philosophical discussions about nature were inadequate, and that henceforth only repeatable empirical experiments and evidence were to be acceptable. Einstein’s thought experiments were the forerunners of the computerized model, with its GIGO results possible with every character of code written. Too much “science” today is done in the imaginary world of models and thought experiments, not to mention mathematical “realities” such as string theory, the Oort cloud, dark matter, dark energy and chaos theory – all of which have convinced many in science they are reality, when in reality they are only mathematical concepts. Some have proven out (not those two), but many, many mathematical concepts never translated into reality, even though they are accepted at this time. I consider thought experiments to be nothing – less than nothing, even dangerously misleading in some cases – until proven by empirical, reproducible experiment. I think most of those mathematical constructs are horrible science. It is pretend science, IMHO: convince enough people with your equations and models, and the Emperor doesn’t even need clothes. The thinking inside the box is today the courtiers afraid to admit the Emperor is naked.

    Einstein took us back to philosophical arguments about nature, cloaked in math. And no one even noticed. It is arguments over how many angels can fit on the head of a pin. But today the angels are called Higgs-Bosun particles, or the strong force, or the weak force, or neutrinos or…

  20. Steve, Dennis:

    For a nuke bomb in space, there is not much of blast wave, as people have pointed out.

    For the dirt clod of Dennis, if you don’t like it, put mushy comet, dirty-snowball-with-ravel mixed inside, I think, not the nuke exploding.

  21. Herman –

    Wait a minute. Are you sure about that?

    Project Orion, led by Physicist Freeman Dyson (a man I highly admire) was about using small nuclear explosions for rocket propulsion. According to Wikipedia, the propulsion was in the meganewton range. Dyson was quoted as seeing this as the means of interplanetary ttr5avel around the solar system, even a 1-year trip to Pluto!

    The acceleration was in the range of 20-30 m/sec for unmanned flights.

    That is a lot of acceleration.

    All this seems to conflict with what you are saying Hermann.

    If the Wikipedia article is correct, a variation on Project Orion would be the solution for a solid comet – just design it to land nose downward without crashing, and then start firing the nukes.

    For a mushy one, though, Dennis raises good questions.

    But Hermann, can you address these assertions in Wikipedia?

    I will go searching for more info and report back.

  22. Oh, I see I didn’t exactly spell out that I could see using that design to PUSH the comet sideways (or up and out of the plane of the Earth’s orbit). At the same time,if Freeman Dyson said that nukes in space could provide acceleration, I would think explosion(s) directly against the side of the comet would provide some large amount of impact on the comet. If 50,000 Gs comes from 1/4 Kt nukes, then using something really large would provide enough to do some heavy damage to the comet. A single 50 megaton nuke (equal to the largest ever tested) would impart about 200,000 times the thrust/impact as those puny A-bombs.

    (Last year I had reason to look up all the A-tests the U.S. did. I did not understand their testing <1 Kiloton nukes. It seems Operation Orion might have been the reason.)

    In the case that exploding not an option, pushing the comet aside rather than pulverizing it sounds like a possibility, if we can land on side or front of the comet. (Front would decelerate the comet, which may take less force and/or less time to effect the braking. It might be best to make it arrive late to the impact point, allowing the Earth to go by unscathed.

    Online I found and downloaded the "Nuclear Pulse Space Vehicle Paper" that General Dynamics wrote up.

    The thrust was actually designed in the 6-20 megaNewton range, nominal, with an earlier well-studied version targeted at 44 megaNewtons.

    The design also uses shock absorbers on the back end so that the blast would not destroy the ship with the impact of each blast. That idea could even be utilized to cushion on the other end, the front end. That way the push impulse could be made even more gentle so as to keep the comet from disintegrating. Some energy is lost, of course, in absorbing the shock. Similar shock absorbers as at the back would be designed robust enough and energy dissipative enough to work at the front end, too. A lighter shock absorbing version at the front would give the about the same performance in the front as the back, but the already dampened shock would be smoothed out even more so, and that is good.

    The rear shock absorber was designed to reduce a 50,000g impulse to about 3 Gs for human journeys. That level of smoothing out the blast impulses is what would also be needed in the front. Attaching to the comet would need to be worked out, to distribute the remaining thrust over as large an area as possible. That 3 Gs may be gentle enough to keep a slushy comet together.

    Instead of a front shock, then, some sort of self-inflating, self-conforming spongy material that hardens would be good, to make sure the loading against the comet is not point loading. What material would work in a vacuum would need to be worked out.

    Now, 3 Gs is almost certainly not good enough acceleration. So it would necessitate working it out starting with the acceleration needed to make the comet clear the Earth by an optimum distance. With 50,000 Gs already designed for, for simply the rocket, there just might be enough acceleration to actually DO the job. I had not thought this much thrust was available. A look at thrust-to-weight ratios would refine and inform the design. A 10km comet is certainly larger than the rocket by a large factor. Yet any force being applied would redirect the comet to some degree.

    If necessary, the design should be sized up, if time allows that.

    The rocket on paper was designed for 800 to 900 separate impulses/nuclear explosions.

    While this may not be the perfect solution, the work done in the 1950s would be a really good starting point, and the work done then may guide present efforts.

    It might be a decent way to get rid of some nukes, too.

    I had no intention of typing that much in this comment. Sorry. I got terrifically interested in this.

  23. Are we going to discuss impact science, and related catastrophes? Or are we going to review science fiction?

    Freeman Dyson is a physics professor at Princeton who came up with some great science fiction ideas. My favorite idea of his is the so called “Dyson Sphere” where a giant enclosure is built around a star, with the inner surface of the sphere at just the right distance from the star to support life. A variation of that idea was to build a flat ring around a star with the diameter of Earth’s orbit. Another SF writer named Larry Niven wrote a pretty good book called ‘Ring World’ using that idea. And he used Dyson’s nuclear propulsion ideas in a book called ‘Footfall’. But outside of highly imaginative science fiction, is there anything in refereed literature, to support the feasibility of Dyson’s idea for a multiple explosion, nuclear propulsion system?

    Got any real, tested, engineering, or feasibility studies, you can cite giving material specifications for the fabrication, and launch into orbit, of the components of the blast/heat shield? Or those giant shock absorbers on the ass-end of the thing?

    I’d also be interested in in reading of any peer reviewed work that predicts the effects of a nuclear blast wave in space on the debris field of a fragile, or fragmented, icy body, or comet

  24. Yes, Dennis, in fact I do. I am glad you asked.

    You don’t know what you are talking about.

    General Dynamics was one of the primary movers and shakers in defense systems in the post-WWII era. They were not a science fiction corporation. Here is THEIR real, non-science fiction : http://www.scribd.com/doc/28668567/Nuclear-Pulse-Space-Vehicle-Study

    Defense contractors don’t do science fiction. They do real things and won’t take on something if it isn’t a real possibility. They sometimes do peer-reviewed papers, but therei thing is to make REAL systems, ones that are engineered, not theorized. If GD did this “paper”, as you would want it to be called, they would have identified and made real world calculations of every system in it – which you may read through. Those 175 pages are not science fiction.

    As I said, at the Nevada Test Site, the U.S. military ran by my count 63 tests of fission bombs 1.0 kilotons or less from March 1953 to July 1962. They also ran another 42 similar tests with expected yields of 1.1 to 5.0 kilotons from Jan 1951 to Jun 1963. These tests were not done with blowing up cities in mind; they were done as part of an effort to find out what was the capacity of this new technology. Those tests cost many billions of dollars and were ended only because of the Nuclear-Test-Ban Treaty in 1963.

    I’d not understood the small tests before. Now I have a sense of them.

    Not one thing about the nuclear testing program was science fiction, Dennis. You are too young to know what the depths of the Cold War were. I was, too, but as a kid knew we were all in thousand times more at risk from nukes then than we are from terrorists now. There was no test done that did not have real world applications.

    Your disdain of Dyson only shows your ignorance. He is not a science fiction writer. Although he did not work on the Manhattan Project he was a peer to the physicists who did – Einstein, Richard Feynman, Niels Bohr, Enrico Fermi, Hans Bethe, Edward Teller, J. Robert Oppenheimer.

    Dyson has been at the Institute for Advanced Study at Princeton, where he has been since 1953, when Einstein was still there. Yes, he is still alive. And at age 88, he is still producing.

    Dyson is a scientist. He has 21 honorary degrees, from such colleges as Oxford.

    You heard of his Dyson spheres and thought it was science fiction. And in your laziness (which only takes a few mouse clicks to cure) you didn’t even bother to look up who the guy is, thinking he was some joke on Star Trek.

    From Wikipedia:

    From 1957 to 1961 he worked on the Orion Project, which proposed the possibility of space-flight using nuclear pulse propulsion. A prototype was demonstrated using conventional explosives, but a treaty which he was involved in and supported, banned the testing of nuclear weapons other than underground, and this caused the project to be abandoned.

    From the New York Times’ 8,000-word article on Dyson, March 23, 2009 (http://tiny.cc/28mo3):

    From 1957 to 1961 [Dyson] worked on the Orion Project, which proposed the possibility of space-flight using nuclear pulse propulsion. A prototype was demonstrated using conventional explosives, but a treaty which he was involved in and supported, banned the testing of nuclear weapons other than underground, and this caused the project to be abandoned.

    The Nobel physics laureate Steven Weinberg admires Dyson’s physics — he says he thinks the Nobel committee fleeced him by not awarding his work on quantum electrodynamics with the prize.

    Defense contractors do not design, build and test prototypes of science fiction. Hundreds of thousands of hours of science and engineering went into the Orion Project.

    The only reason it was shelved was because of the Nuclear Test-Ban Treaty in 1963 and the public concern with nuclear products having been discovered in food stuffs in 1959. Otherwise it is a certainty that we would have seen it happen.

    It would be useful to inform yourself before going all superior with your Start Trek knowledge, Dennis.

    Since you are the one who talked about the “eating dust” theory of blast effects on fragile, fragmented bodies in space, I propose that you do your own search instead of asking others to do it. You couldn’t even lift a finger to find out that Dyson Freeman was a real Nobel-level scientist of over 60 years.

  25. I never said I didn’t respect Freeman Dyson’s work; or the man himself. I think he was a brilliant, and visionary, scientist.

    But I do think the Orion project should remain under the heading of science fiction. For obvious reasons, the nuclear testing they proposed was never done. Their prototype device used conventional explosives, not nuclear. And your statement that defense contractors don’t do science fiction is naively absurd. Government contractors of the military industrial complex are notorious for wasting a lot of money on unworkable science, long after it becomes clear an idea is unworkable, or impractical.

    The statement that I am too young to “understand the depths of the cold war” is also mistaken. As a little boy I remember hiding under the desk when there was an air raid drill. And my first assignment in the U.S. Army was with Headquarters, and Headquarters Company, 94th Air Defense Artillery Group, in Europe.

    In the early ’70s, while the rest of the country, and NATO, still had their attention distracted by the War in Viet Nam, we were the folks who were on 24/7 alert status with a continuous line of radar installations, medium range missile batteries, and Nike Hercules anti-aircraft batteries, stretching the full length of the Iron Curtain. Every weapon we had was pointed east. And some of them were nuclear.

    During the early ’70s the cold war was still in full swing. And at a time when both sides were at the peak of their nuclear destructive capabilities, we were some of the guys who lived full time looking at radar screens. And ready to fire our missiles at a moment’s notice. We knew full well that we were the first line of defense against any attack from the east. We also lived with the knowledge that we were a very important first target for the other side. It was a dangerous, frightening, nerve-racking, game of cat and mouse. And the soviet bombers would typically wait until the very last minute to turn back.

    There were many opportunities for catastrophic mistakes on both sides. And many close calls. And the Cuban missile crisis was not the closest we ever came to a nuclear exchange with the Soviets. As far as close calls go, it was only the most public.

    If the Soviets had attacked western Europe during that time, we would’ve been the first to see them coming. We would’ve been the ones who notified NORAD. And it would’ve been after we fired our first anti-aircraft missiles at the incoming bombers.

    You’re partially right though, I never did understand the logic of the ‘cold’ war: I just fought in it, on the front line. And I was blessed in that I never needed to fire a shot.

    As for your claims of my ignorance….

    I won’t dignify that personal insult with an answer.

  26. Dennis –

    I guess you are older than I’d thought. My bad. I do stand corrected. Consider me chastised.

    By odd coincidence, I was stationed at Nike missile bases myself, stateside, with USASTRATCOM outside Detroit and Cleveland, in the Signal Corps. I will say one thing about science fiction: Our capacity to protect the U.S. cities was a total fiction. Not with those missiles. In exercises, we couldn’t even “hit” incoming missiles with more than about 30-40% success, and that was in simulations that weren’t really tested against anything real. Pittsburgh had “only” 6 of 9 get through. When one would wipe out Pittsburgh, I knew our belief that we were safe was a total joke. But we played the game. We didn’t have to face anything more real than someone failing to give the right IFF code. And based on the lack of success of shooting down just aircraft, even up till now, all of that was us stroking ourselves.

    I was the first soldier in Signal Corps classes in over a year that didn’t get sent to Viet Nam, so I know what you are talking about, the focus being so strongly on Nam. Everyone else I was stationed with went to Nam, either before or after. I actually got orders to go to Germany after a while and was able to get out of it.

    There is a huge difference between science fiction and trying out ideas that don’t pan out. But the Orion Project not only isn’t just some idea that wouldn’t have worked. After looking at the plans I am certain they would indeed work. But I wouldn’t want to be underneath it when it took off.

    At the same time, if it were launched from the moon, I think it is plenty doable.

    After doing a spreadsheet on the nuclear tests they were running in Nevada at the very same time Orion was in the works, I am 99% certain that the two developments were connected. Orion with its magazines for holding 800-900 nukes needed them to make sure the nukes themselves worked.

    Besides the 105 tests of 5 kilotons and less (out of 330+ tests), there were 54 others below 20 kilotons and 63 exactly 20 kilotons. The 20Kt ones were also exactly what they were intending to use on the Orion project. And of the 63 20-Kt ones, 61 of them were right during Orion – squeezed between the first U.S. manned flight and the Nuclear Test-Ban Treaty. After Sputnik and Gagarin, the U.S. push on science education and trying to catch up and get ahead of the Soviets was a VERY big deal. Our first rockets were pieces of crap, but they were bound and determined things weren’t going to stay that way. Orion was no academic exercise.

    Those people had every expectation of making that work. It was the public outcry about Strontium-90 in the milk and Kennedy that killed the project, not its unworkability from an engineering standpoint. I am glad they stopped it, but right now, I think it might be worth dredging up and re-thinking, for planetary defense.

    After looking at the plans, I do think that that bugger is our likeliest hope of intercepting incoming comets.

    The big problem with rockets as we use them is that there is almost no fuel left after getting them into space. They all coast for 99% of their flights. A flight to Mars would only take a few weeks if we could take enough fuel to provide 1 G-force of acceleration to the midway point and then 1 G back. But we have so much mentality of doing the coasting thing that we never have taken up enough fuel to do any serious maneuvering. It is all flight path selection and little tweaks to speed. There is so little side-to-side maneuvering I am not sure we even have anyone who could do it.

    The coasting kind of rocketry is not what is needed. Yes we can fly by a comet and hit it – ONCE. A drive-by shooting. I am certain that one hit isn’t going to do enough. We need something that will fly near it, match its speed, drop a nuke, back away, and then drop another nuke, perhaps several in sequence. I can’t see a space capsule or a one-shot rocket moving a 10-km comet – mushy or solid either one.

    I’ve been basically disdainful of what options I’d seen before I got a gander at Orion. From an engineering standpoint, this is a nice project, plenty doable, even though a big one. There was NO portion of the technology that was beyond our capacity to make work in the 1960s, and those are even much more doable now. The radioactivity? You have to assemble it and fire it on the moon or in space. In space is probably beyond our capacity (too slow), so the moon is the best bet. IMHO.

    The biggest H-bomb exploded so far is 58 megaton. One of those isn’t going to do the job. We need to double whammy it or better. Putting up a 100Mt or 200 Mt is not something we can do now. All our real nuclear engineers are dead or dying. 50Mt is about all I think we could send.

    None of this is science fiction. It is engineering. Engineering is the farthest thing from science fiction there is – it is all hard-nosed practical design decisions, choosing options that work and work together. It would be cool being on the design team that saves the world.

    I guarantee all the problems would get worked out. The blueprint already exists.

  27. BTW, when prototyping something as new as Orion was, what you do is make prototypes of each trouble/complicated part of the design, isolated. And my preferred order of tackling things is to get at the biggest problem first, to make sure you’ve gotten that ironed out. In the Manhattan Project, Alamagordo gets all the glory in the history books, but what was going on at Hanford and Oak Ridge had to be built and tested at the same time, to make the all-important U-235 and Plutonium.

    On the Orion Project they did the two biggest things at the same time, too. One was that non-nuclear pulsing drive prototype. The other was developing the nukes themselves.

    They tested lots of 20-kt nukes. 29 of the last 31 tests before the Test-Ban Treaty went into effect were 20-kt. There had to be a reason. That was between early November 1962 and late June 1963. The treaty took effect in July 1963. They got their testing in under the wire. By the early 1960s they didn’t need to explode a bunch of 20-kt nukes to educate themselves about 20-kt fission bombs and their yield or their radioactivity, not in a general sense. Repetitive test like that happen when you are trying to make something more consistent. And what other reason would they have, than Orion? Not for bombs you’d drop on a Soviet city, not when you had H-bombs for that.

    This was when Dyson was running the science side of things for Orion.

  28. Dennis,
    you must be about my age or a little younger. My earliest memories are from before WWII and I remember the start of the war with many details.

    Steve: My main concern about deflecting comets is that they seem to be so fragile almost anything you do is going to make a big mess, resulting in a huge cross-section of the debris stream, multiple catastrophic impacts more likely, on Taurid scales or worse. Early detection is another difficulty. How many years in advance are needed to prepare a defense? We need to ask comet experts about what time frames exist, my guess is for most comets not much more than a year or less. Asteroid (dea comet?) Apophis could be a test case.

  29. One aspect of ET (~comet) impact frequency underestimation is limited study of the influence on human evolution, except on this blog, where many comments speak to this, much ignored. Facts of geography of hominid tribes or clades are explained from local extinctions creating isolates, or, food shortages driving groups to migrate over large distances, on land or over sea. E.g., austral populations once stretched from E Asia to Aden w/o interruption but Ainu ancestors became isolated from the clade by the Australasian tektite impact, as did the Aussie Aborigines, etc, etc.

  30. The biggest problem as I see it, is in positively identifying the planetary scarring the catastrophes of the past produced. Many of us have theories of what the nature of that scarring might be. Harlan Bretz showed us that aerial photography can go a long way in identifying catastrophic mass movement of terrain features. And in scoping out likely candidates for field work. Depending on one’s level of access, high resolution satellite imagery of 1 meter per pixel, or better, is available for most of North America.

    But no one’s ideas of planetary scarring will be proven without good field work, and detailed analysis of rock specimens from suspected impact sites. Many of us have a long list of places that are begging for a visit. And I’m sure Ed has a few places of his own. Most of what I would consider the most important places on my list have remained unstudied, and unmapped, for so long because they are in extremely remote, and/or inhospitable locations. And they will be a logistics nightmare to get to.

    There’s no shortage of world class impact scientists, with well equipped labs. And who are willing, and even exited, receive specimens from field researchers. So it isn’t a problem of the lack of good researchers. Ed is right that the major problem is funding.

    The TV show on the discovery channel called The Meteorite Men might be a good example of one possible way to overcome the funding issue. Geoff Notkin and Steve Arnold, have made a pretty successful show wandering off into the middle of nowhere, and finding meteorite fragments. So it’s clear that there is no shortage of public interest.

    What if some of us put our heads together, and did a show called ‘Crater Hunters’?

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