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A Defense Against Planetary Attack

Normally the term ‘planetary defense’ conjures up images of an incoming asteroid, spotting (let’s hope) way out in the Solar System. The defense mounted against pending disaster might involve nudging the asteroid gently out of its current trajectory so that it misses the Earth. Various scenarios come to mind for managing this, but all involve getting to the dangerous object in plenty of time so that technologies not so different from what we have today will be effective at ending the threat.

Planetary defense book

With that in mind, I did a double-take when I saw the cover of An Introduction to Planetary Defense, by Travis Taylor, Bob Boan, Charles Anding and Thomas Conley Powell. The book, published by BrownWalker Press at the end of 2006, bears this subtitle: A Study of Modern Warfare Applied to Extra-Terrestrial Invasion. A jeu d’espirit based on SF themes? Hardly. The authors are familiar names whose work has resonance.

Taylor, for example, has worked for NASA and the Department of Defense for sixteen years and has collaborated on interstellar topics with Greg Matloff. Powell is senior scientist for BAE Systems in Huntsville and is an expert on space trajectories, attitude dynamics and orbital mechanics. I’m less familiar with Boan and Anding, but each seems to have experience in space systems. So when this group tackles extraterrestrial invasion, they do it soberly, with a hard look at strategies, tactics, and weapons that might be used if the longshot scenarios of some science fiction authors — or even B-grade movie directors — ever become reality.

You can find excerpts from the book at the publisher’s website, from which I’ve extracted the introduction and part of the first chapter as I wait for my copy to arrive. Interestingly, the authors take a hard look at the Drake Equation in that section, and also ask how long any civilization could remain hidden from a more advanced culture. We’ve discussed that question in these pages before, in reference to Earth’s everyday electromagnetic radiation and whether radio and TV broadcasts from the past seventy-five years would be detectible from nearby stars, with the general consensus being that such a detection is highly unlikely.

But what about other forms of detection? These writers doubt that any civilization could remain hidden for long. Here’s an excerpt about just one reason, the advent of new imaging and telescope technologies:

Recently in his book The Sun as a Gravitational Lens: Proposed Space Missions, Claudio Maccone, a space scientist at Alenia Aerospazio in Turin, Italy, suggests implementing the sun’s gravitational lensing effect (as predicted by Einstein’s General Theory of Relativity) in a telescope. In other words, the Sun could be used as a lens producing an aperture the diameter of the sun. Its focus is at about six hundred astronomical units away. If the proper equipment were placed at the Solar focus, extremely detailed images of extra-solar planetary surfaces could be captured. Civilizations only moderately more advanced than we are could quite possible implement such a telescope. Therefore, even quiet civilizations could be seen through such a telescope. Eventually, detection of such civilizations may not depend on their directly communicating with us by sending signals. The lght from their star boucning off of their alien rooftops and then onward to our giant telescope may be enough.

Hence the conclusion: All intelligent civilizations will eventually be detectable by more advanced cultures. That’s an interesting value to plug into the Drake Equation! Developing the statistics on probable life elsewhere makes the book’s point — we have no real notion of how such civilizations might deal with us, and should learn the lessons of history by way of developing a strategy for dealing with unexpected arrivals. Based on its first chapter, this book seems to be stuffed with interesting notions. Between it and Michaud’s Contact with Alien Civilizations, we’ll have plenty to read and discuss on potential SETI outcomes.

Comments on this entry are closed.

  • A Babe in the Universe January 7, 2007, 13:25

    Ever see the old Gerry Anderson series UFO? That’s the way to defend the Earth–with purple hair!

  • Malcolm Ramsay January 7, 2007, 13:34

    Which is why the dream of manned spaceflight foundered after Apollo 17- not enough silver clothes and purple wigs! NASA, take note; get those into the moonbase budget now

  • Eric James January 7, 2007, 13:49


    I’ve tried posting this several times. Is there a problem I should be made aware of?


    Ah ha! Vindication. As I’ve pointed out several times before, we can’t hide from an advanced species. Why bother trying?

    An even more advanced species might use a local, compact dark object for a lens (potentially many times more powerful, with very clear images (no solar haze to worry about)). Can you even imagine the potential?

    I think the idea of trying to defend ourselves against a species that might move en masse against us is ludicrous though. They’d only need to pick up a few kuiper belt objects on their way in to bombard us with, and it’d be all over. We’d need to be much more advanced than we are, with outposts everywhere, to even begin to develop a viable defense.

    Our only current hope against such an invasion is that it can’t happen. The reasons might be that it’s physically too great a task (relativity rules), no advanced species evolves with such aggressive tendencies intact (evolutionary exclusion), we’re of the first generation of technological civilizations (we’re alone), or the Galactic Counsel crushes any such aggression (illegal).

    In my mind, the Fermi Paradox clearly indicates the likelihood of the first, second, and/or third. I also fear that intelligence and technology may be evolutionary dead ends, leading to an inevitable self-annihilation (I hope not).

    My fears of that last would be greatly alleviated if we were to establish viable, permament settlements on other worlds. Let’s get to it.

  • Administrator January 7, 2007, 14:03

    Eric, the comments problem seems to be resolved — turned out to be a database error that is now fixed.

  • andy January 7, 2007, 17:33

    Again the detectability issue comes up, this time in regard to gravitational focus telescopes.

    However there are a lot of stars to survey, and gravity telescopes are difficult to aim! For example, using the Sun, a gravity telescope is only possible beyond 550 AU. The semimajor axis of the Alpha Centauri AB pair is 17.6 arcseconds, which would entail moving the telescope 7 million kilometres to change whether Alpha Centauri A or Alpha Centauri B is being focussed on!

    Therefore it is still going to be exceedingly difficult to check a large number of stars, unless the aliens are fortunate enough to have a compact star (e.g. a white dwarf) to hand.

    So unless there is some specific reason to pick our system as the target of a gravity telescope, or building lots of telescopes hundreds of AU from the home star is a lot less expensive than it would at first seem, this doesn’t seem to be a good reason to assume we are automatically going to be detected.

    Detecting a transmission, on the other hand, would represent a very good reason for launching a telescope to a location where it could survey the source system!

  • Fred Kiesche January 8, 2007, 16:00

    Taylor is also the author, co-author or “consultant” on a couple of science fiction novels which definately hearken back to the “Golden Age” style of “Doc” Smith. Take a look for “Warp Speed” and “Quantum Connection” (connected). He “consulted” for John Ringo’s “Through the Looking Glass” and co-authored “Von Neumann’s War” with Ringo. For that one he wrote a short work, a fictionalized NASA/DOD style report called “Neighborhood Watch”.

    He is an active presence at Baen’s Bar (online discussion for Baen Books author).

    Gosh, can you tell I’m a raving fanboy or what? Heh.

  • Administrator January 8, 2007, 18:13

    Fred, I did see that Taylor had done some work on SF novels, though I didn’t know anything about them. Interesting! And by the way, I should tell you how much I’ve enjoyed following your reading lists on Eternal Golden Braid. Here’s the link for those readers that don’t have Fred’s weblog address:


    You make me realize how much good stuff I have yet to get to. The Ballantine fantasy series is always attractive; I have most of those in first-run paperbacks, but I bet I’ve only read a fraction. I also like the idea of revisiting Jack Williamson. Keep those lists coming!

  • Radu January 8, 2007, 19:51

    I’ve only read the first 25 pages (available for free). The values in Drake equation are highly overestimated in my opinion. For instance, probability that the simplest forms of life would evolve into inteligent life is estimated at 0.67.

    Congrats to authors for attacking a highly debatable subject, but I’m afraid this will only remain a nice theoretical exercise.

  • Adam January 9, 2007, 1:54

    Hi Paul

    The unintended humour of the bookcover is a subtle joke I suspect. The “Saucer” on the cover is the Viking aeroshell from a NASA painting – and a famous news-article on “Viking” was entitled “The Viking Invasion of Mars”.

    Of course we could all pick up a few “World War” novels from Harry Turtledove to see how to REALLY fight aliens with 1940s style technology too.


  • Alexander January 9, 2007, 5:00

    >using the Sun, a gravity telescope
    >is only possible beyond 550 AU

    I am not a specialist in gravitational lensing, but it seems to me that there is a big difference between gravitation focusing with black hole (which is not emit of light and solar wind) and gravitation focusing with the Sun (or with the similar ET mother star)? I think, fluctuations of solar wind will lead to defocusing action, blur the picture and thus we can not focus weak ET’s signals (the same as, ETIs can not focus our weak signals)…

  • Administrator January 9, 2007, 9:12

    I believe Claudio Maccone gets into this focusing problem in his book. It’s a factor he thinks can be surmounted, but let me drop him a note asking for a more detailed comment on this, Alexander.

  • Dan Neely January 9, 2007, 19:17

    The mass fraction of the stellar wind relative to the rest of the star is essentially zero for any star except a red supergiant. It’s a nonissue.

  • Alexander January 10, 2007, 4:29

    The Sun (solar) wind acts on EM-waves propagation not by means of its mass…

  • Administrator January 10, 2007, 8:25

    Von Eshleman, according to Claudio Maccone’s book, has studied the effects of plasma above the surface of the Sun on gravitational lensing. He discusses what he calls the ‘plasma lens,’ the deflection of light rays due to the plasma properties of the corona. Maccone runs through the equations for all this in some detail in his book, all of it complicated by the fact that, as the author says, “As of the year 2001, no scientist seems to have derived an adequate mathematical model of the solar Corona. This is because there are so many quantum and statistical phenomena taking place in the Corona that a full mathematical description turns out to be extremely complicated.” The math that surrounds this statement is quite complex and well beyond my powers, so I’m still hoping for a response from Dr. Maccone on the corona and solar wind questions.

  • Administrator January 10, 2007, 20:43

    This word just in from Claudio Maccone re gravitational lensing and solar wind defocusing, in response to Alexander Zaitsev’s original point: Dr. Maccone points out that the defocusing effects of the solar corona are indeed an issue, much more so than the solar wind. And he goes on to say this: “However this problem may be solved by sending the probe FURTHER OUT than just 550 A.U. In fact, the solar gravitational lens is “peculiar” in that every point beyond 550 AU STILL IS A FOCUS! It simply is the focus of those light rays (or radio waves) that are not grazing the Sun surface (as those focusing at 550 AU), but passing at a minimal distance from the sun center HIGHER than the sun radius. This pushes the distance that a probe has to reach further out than 550 AU, where the probe will be hit by radio waves that passed away enough from the Corona not to be defocused any more.”

    Many thanks to Dr. Maccone for this additional information. Those interested in checking out this issue in depth should get a copy of Maccone’s The Sun as a Gravitational Lens: Proposed Space Missions (ISI Press, 2002), the definitive work on the subject.

  • andy January 11, 2007, 18:31

    Of course, pushing the probe out beyond 550 AU makes re-aiming the gravity telescope even more difficult as the distances get larger. Doing a full-sky survey with such a telescope would effectively be the same as creating a Dyson swarm at >550 AU, which surely is not a very practical undertaking!

    Also bear in mind at those kind of distances it isn’t particularly easy to power the spacecraft. Given the existence of technologies such as solar sails, it may well be easier to send another telescope out beyond 550 AU than move an existing one. This would mean having to choose targets very carefully!

    So while a civilisation presumably can be easily monitored by such a device, the economic cost of performing a survey in this way means that it is highly unlikely anyone would detect a civilisation using this (unless radio-emitting civilisations are extremely common in the galaxy). Unless we give the aliens a reason to monitor our star system (a METI effort) with a gravity telescope, it probably isn’t going to happen. Arguing against METI-caution on the basis that we’d be detected anyway by gravity telescopes doesn’t hold water.

  • ljk January 11, 2007, 19:35

    One reason they might monitor the Sol system: If they
    are advanced enough for space travel they certainly should
    know that stable yellow dwarf stars are potentially good
    places for harboring life-bearing planets, even if they did
    not come from a planet with a Class G sun.

    But with so many stars in the galaxy, it would take a very
    long time to search them all out, whether at a distance or
    exploring systems directly.

  • ljk January 19, 2007, 11:36

    French Astronomer Designs Telescope of the Future

    Just finding other Earthlike planets is a big enough challenge for most astronomers. Not Antoine Labeyrie. Hes already dreaming of a telescope powerful enough to make out continents, oceans maybe even signs of life on their surfaces. It wont be easy, but its not impossible either, says Labeyrie, an astronomer at the Observatoire de Haute-Provence in France and a world-class designer of telescope optics. In fact, his proposed Exo-Earth Imager (EEI) could show astronomers an Amazon-size forest, with its green hint of biology, on an Earth-size planet 30 light years away.

    Full article here:


  • ljk June 1, 2007, 9:36

    A criticism of the book here:


    The book focuses more on an attack as if from a regular
    human invasion force rather than sophisticated ETI from
    another star system.

    For example, they fail to mention how a single starship
    flung at us at relativistic speeds would wipe Earth out
    in one shot. If the aliens decided to be a bit more
    strategic, a few well-aimed space rocks could take out
    our civilization in no time.

  • Adam June 1, 2007, 17:02

    Geez Larry… you have to keep mentioning relativistic missiles! I’m getting paranoid about them! We need tachyonic RADAR and some maneuvrable masses to put in the way of any incoming masses doing 0.99c… and we need them NOW!


  • ljk June 2, 2007, 1:27

    They will also teach to start getting our eggs out of this one
    basket called Earth NOW.

  • ljk June 27, 2007, 10:07

    Nice blog article from Sentient Developments on why if aliens
    wanted to wipe us out they already would have: