Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Will nuking jupiter start a helium/hydrogen fusion reaction?

  1. May 12, 2010 #1
    ala the sun?

    Jupiter's upper atmosphere is composed of about 88–92% hydrogen and 8–12% helium


    considering many nuclear weapons have a fusion stage

    would the explosion propogate?

    what would rain on my parade?
  2. jcsd
  3. May 12, 2010 #2
    No. Jupiter doesn't have the mass to sustain nuclear fusion. If it did, it would already be a star.
  4. May 12, 2010 #3


    User Avatar

    Staff: Mentor

    ...and even then, it wouldn't explode, it would just be in an equilbrium state, fusing at a certain, relatively constant rate.
  5. May 12, 2010 #4


    User Avatar
    Gold Member

  6. May 12, 2010 #5
    I would first want to know how the energy of a fusion bomb varied with the volume and how much energy we could pack in some small volume? Say all the energy of the bomb is absorbed by some shell of Jupiter's atmosphere surrounding the bomb. This energy will raise the temperature and density of this small shell of gas. If the energy released by the bomb is large enough the gas will be hot enough and dense enough to ignite? I don't know if you can simply argue that no additional energy is produced, seems there would at least be a little extra from unlikely events? Or is it that you just can't pack enough explosive energy a small enough space for the case of Jupiter?

    But what if we had a cold dense star of hydrogen, no thermal motion. Not so dense as to form a neutron star. Now lets set off a fusion bomb, are conditions now different?

    Thanks for any help!
  7. May 12, 2010 #6


    User Avatar

    Staff: Mentor

  8. May 12, 2010 #7
    The reason stars are able to form stable fusion reactions is because their enormous gravity is great enough to balance the enormous outward pressure produced by the reaction, and that their high gravity creates the initial pressure needed to ignite the reaction in the first place. You can't just have a "cold dense star" made of hydrogen - if it's so dense to sustain fusion, it will inevitably ignite on it's own. If it's not dense enough, any fusion pressure would cause the star to swell, and then you'd lose the pressure needed to sustain the reaction...
  9. May 12, 2010 #8
    How do you know that? Surely there's a high activation energy barrier to ignition, and after ignition there's far more energy available to sustain the reaction. (There's plenty of examples in nature, of stable things that just need some external impetus after which they can sustain a very different state.) I don't know whether or not your claim has any truth to it, but don't you need the support of some kind of modeling to be able to be convinced of your statement? (Are you actually trying to argue that the heat of Jupiter's coalescence was enough to ignite any potential fusion processes, and that it has since petered down?)
    Last edited: May 12, 2010
  10. May 12, 2010 #9
    It really doesn't have to do with heat in the way a chemical reaction does... what matters is gravitational pressure.

    The outward pressure of a nuclear reaction is enormousness... think of the energy released by a nuclear bomb, except millions of times larger and occurring every single second for millions or billions of years on end. If the star doesn't have sufficient mass, this pressure will simply blow the star apart, and the reaction will halt. You need a large enough mass to continue to squeeze the core of the star to at least the critical pressure after you've already fought off the pressure the fusion is generating.

    The "activation energy" comes from the gravitation it's self, and should actually be less than the energy needed to sustain the reaction. Therefore, it is impossible for a star to have the mass necessary to sustain the reaction without actually igniting.
  11. May 13, 2010 #10

    thanks for clarification!
  12. May 13, 2010 #11


    User Avatar
    Science Advisor

    Although a sustained reaction could not occur, some hydrogen would fuse, would it not? Other than the hydrofen inside the bomb, I mean.
  13. Feb 29, 2012 #12
    The heat of the comet hitting Jupiter was easily much more than any bomb we have made or would expect to make.
    Jupiter's existing very slow rate of fusion could only be increased by making it more dense in a way that does not poison the fusion chain reaction. Since almost any dense material would poison a chain reaction, I'd say its almost impossible. A possibility might be to get a couple teratonnes of fissionable isotopes in there, so that the core was raised in temperature from what would essentially be an unmoderated gas-core fission reaction.
  14. Feb 29, 2012 #13


    User Avatar
    Staff Emeritus
    Science Advisor

    Wizwom did you know the last post in this thread before you was almost 2 years ago? :tongue2:
  15. Mar 2, 2012 #14


    User Avatar

    ... and, besides, I don't think PF should condone the unprovoked bombing of an alien planet!! :tongue:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook