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Why is a comet worse(asteroid)?

  1. Apr 10, 2007 #1
    There's all sorts of speculations about Earth's distruction. Some say it's going to end as the words in the Bible and Mayan calender say in 2012. No without majic the only way this cn occer is Science.

    An asteroid aside from a super volcano i s the only thing I know that could bring about worldwide destruction. But they say there is something worse, something that can reck more havock... a comet. A comet is mroe dangerous and destructive, but why> Is it moving faster, is it heavier? The Bible codes which some are written by ETs say that a comet is coming for us.
    My question is how could a comet take us by surprise? Besides being larger they have a large tail that's clearly visible once it crosses Jupiter's orbit. We could have several months toa years warning. We could atlast try to send some nuclear warheads.
     
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  3. Apr 10, 2007 #2

    Nereid

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    Not sure that religious texts have any relevance in this part of PF, but to answer your questions:

    * a comet may be less destructive or more, than an asteroid; it depends on many factors

    * one such factor is the mass of the comet (or asteroid); all other things being equal, destructiveness scales as mass

    * another is the impact speed; all other things being equal (and they are most definitely not!), destructiveness scales as the square of the speed

    * a comet may be particularly dangerous because its orbit is inherently unpredictable, due to the rocket effect (much more so than an asteroid's orbit)

    * 'new' comets pose a double threat - if this is their first passage through the inner solar system, there will likely be no 'pre-covery' data that could be used to refine the estimated orbit, AND as a new comet, its volatiles content will be high (so rocket effects greater than for an 'old' comet).

    Nuking a comet would likely be a particularly stupid idea ... the film Deep Impact got that right ... if all the nuke did was shatter the comet into a half dozen big pieces, then the destrutiveness may become much greater.
     
  4. Apr 10, 2007 #3
    You say nuking a comet would likely be a particularly stupid idea. So just in case there's one going to our earth, would we have other posibilities?
     
  5. Apr 10, 2007 #4

    Nereid

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    Quite a few, though the ones to use to best effect depend upon many unknowns (as of today).

    If there were enough time, I think reproducing, or modifying, the natural rocket effect would be particularly effective ... as would attaching mass drivers.

    But perhaps the best would be the 'gravitational tugboat' idea that was outlined (by someone from NASA?) last year (or was it not as recently as that?).
     
  6. Apr 10, 2007 #5

    tony873004

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    Modifying the natural rocket effect, or using the gravitational tractor are ideas that would need to be carried out years in advance. But for some reason, people assume that if we nuke it, we'll be nuking it a few hours before impact, just like in the movies.

    But if we give the nuke idea the same time frame as we're giving to the gravitational tractor, or to modifying the natural rocket effect, then its not such a bad idea.

    Deep Impact may have got it right. If we nuke the comet a few hours before impact, we'll just get hit by all the fragments. (But as I remember, that saved the day anyway). But if we nuke it 10 years in advance (the type of timeframe a gravitational tractor requires), the pieces will be so spread out that they will probably all miss us. It's not going to take too long before the average spacing between the fragments greatly exceeds 1 Earth diameter.

    Nuking it years in advance has another advantage. Since the trajectories of comets are inherently unpredictable, in our effort to nudge it off course with a gravitational tractor, we may inadvertently nudge it from a near-miss trajectory to a collision trajectory. But nuking it will cause it to miss either way.

    Another advantage to nuking it is that we can use "off-the-shelf" technologies. We've already impacted a comet with a projectile. We've got pleanty of nukes. Nothing new needs to be invented.

    But the real danger from comets is that we may not get a chance to do anything. Consider Comet Hyakutake. It was discovered in January 1996, 2 months before its closest approach to Earth in March 1996. Nuking it only 2 months prior to impact would be a bad idea. And even if it was a good idea, we couldn't engineer a mission that quickly.

    The gravity tractor is an attractive idea for asteroids when given several decades of advance warning, especially if the asteroid has a natural chaos-inducing segment in its trajectory. In the case of Apophis, it will strike Earth in 2036 if it passes through a narrow keyhole during its 2029 Earth encounter. It would only need to be nudged about the distance of 2 football fields prior to its 2029 passage to turn its 2036 Earth encounter from a hit to a near miss. Hovering over the asteroid for even a few months would cause the asteroid's velocity to change by 1 millimeter per second. Letting the asteroid cruise for 22 years with this new velocity would displace it a few hundred kilometers, more than enough to make it miss the keyhole. But the gravitational tractor idea doesn't work as well if you don't have a chaos-inducing event such as Apophis' 2029 Earth passage, as such an event allows us to make a big change in its trajectory from a small nudge.
     
  7. Apr 10, 2007 #6

    Nereid

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    If the centre of mass (CoM) of the comet was on a trajectory that intersected the Earth, then a nuked comet would have a CoM with the same trajectory (absent rocket effects, etc). And no matter how shattered the comet might be after the nuke, at least some pieces would likely hit the Earth.

    How many pieces would a nuked comet split into? We don't know, and have no way of knowing. If the comet were Hale-Bopp in mass, even one small fragment hitting the Earth would be devastating (even the smallest of SL9's fragments made a pretty big mark on Jupiter!). Worse, a fragmented (big) comet may need more nuking, multiplying the uncertainties and possible devastation.

    But whatever methods could be used, the longer we have to use them, the better the chance we have of averting devastation (and the sooner we prepare to meet the more likely threats, the greater the chances are we'll have a method that we can, in fact, actually use).
     
  8. Apr 10, 2007 #7

    tony873004

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    But the nuke would perform work on the comet, thereby changing its CoM.

    But even if its CoM were unaltered, when the average spacing between fragments reached millions of kilometers, the odds would be astronomically slim that there would coincidentally be a significant fragment lurking within a few thousand kms of the CoM. The CoM would simply be an empty point in space whose only significance is that it is the mathamatical average for the position and velocity vectors of a family of cometary fragments.

    There are pleanty of families of asteroids in the solar system. These asteroids are believed to be fragmented remains of a larger asteroid. But if you were to compute their CoM, it would be EXTREMELY unlikely that it would be occupied by one of the asteroids.
     
  9. Apr 10, 2007 #8
    So which could cause the most havoc?

    COuldn't we just slow it down? Apply some rockets toit and make it slowly orbit Earth. We'd have a new specimen for Science. I hear the materials in an asteroid or so valuable that they could wipe out the national debt.

    ANd we could nuke it even without enough time. THe problem is it would take a 1,000 megaton warhead to destroy the comet and it's fragments. If misused or malfunct it could cause global choas by itself. A nuek that large would take a rocket larger than The Saturn V. Times likr these we need antimatter.

    And as for religion, the kids at Fatima said the saw The Virgin Mary. SHe said that people would be burned to death looking for water. Bu there will be a ime that day that all the motorss top working. Can a comet or asteroid stop all the motors from working. I know lots of them are made of metal, and that carries a magnetic feild. But doe sthat have enough power to stop all the planet motors from running?
     
  10. Apr 11, 2007 #9
    Gamma Ray Bursts -http://en.wikipedia.org/wiki/Gamma_ray_burst- are also something to worry about :wink:
     
  11. Apr 12, 2007 #10
    That would destroy about a quarter of the galaxy.
     
  12. Apr 12, 2007 #11
    been talking to Line alot, lately? :confused:
     
  13. Apr 13, 2007 #12
    One other possibility :smile:
    Chances are pretty high that there are plenty of alien craft out there at any given time, and they would nudge the impediment well before we ever knew it existed, thereby averting the possibility of an Earth strike. They will let softballs and the like hit us, but an Earth shattering blow will compell them to take action.

    Thanks ET! :biggrin:

    Case closed
    There is nothing to worry about here, and no reason to bend over and kiss yer ass goodbye about, lest you be the unlucky bastard that got hit by a softball.:yuck:
     
  14. Apr 19, 2007 #13
    , I've heard something to the affect that if there was a so called planet X, and it passes through our solar system; the gravitational pull would switch Earths magnetic poles, causing mass destruction (volcano, earthquakes,ect..)
    This is yet another possibility of the end for us.
     
  15. Apr 19, 2007 #14

    chroot

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    There will be no more discussion of religion in this thread; I will delete it. Bible codes are not appropriate material for this site, either -- after all, anyone with a computer can 'find' a Bible code to say anything they want.

    - Warren
     
  16. Apr 19, 2007 #15

    russ_watters

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    No, it isn't. It is just dumb crap made up by a fraud to make money.
     
  17. Apr 19, 2007 #16
    OK- well now I know i guess-
     
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