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Speculate for me

  1. Apr 30, 2008 #1
    im a non-scientifically trained individual, who is toying with the idea of writting a sci-fi novel. I tend to prefer sci-fi that is based on realistic principles, and realistic results as that helps me maintain the "suspension of disbeleif" so key in making a good story.

    Ive also always been tremendously supportive of sceintific efforts and the scientific community, so getting a chance to talk to the "eggheads" is pretty cool in and of itself. :)

    Anyways, As a plot device, i want a ship, carrying a load of anti-matter to loose containment right inside the atmopshere of Venus, say 80 miles up. Im looking to blow maybe 60% of the cloud cover off the planet, crater it, and push into a slightly ellpiptical orbit, requiring a massive amount of international resources to move the planet correctly or destroy it so that it doesn't screw up the solar system.

    Anyways, as a rough estimate how much anti-matter would this take to accomplish, and are there any other effects that such a large explosion would cause that i should be cognacent of?
     
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  3. Apr 30, 2008 #2

    Vanadium 50

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    To change the orbit substantially you need of order millions of tons of antimatter. Calculate the kinetic energy of Venus and you get an idea of the energy needed to change an orbit: a non-negligible fraction of that. Note also that if you don't also change the momentum of Venus, the orbit will also be unchanged.
     
  4. Apr 30, 2008 #3

    vanesch

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    Just to tune in with vanadium, here are some numbers:

    energy equivalent of 1kg of mass (which is liberated when half a kg of antimatter reacts with normal matter): 9 10^16 J or 90 PJ. (peta-joule).

    Mass of venus: http://en.wikipedia.org/wiki/Venus

    5 10^24 kg

    orbital velocity of venus: 35000 m/s

    kinetic energy of venus: 1/2 m v^2 = 3 10^33 J

    This is equivalent to the annihilation of 3 10^33 / 9 10^16 = 3.4 10^16 kg, so you'd need to annihilate half of that (1.7 10^16 kg) of antimatter.

    As a reference, the earth ocean contains about 1.3 10^9 km^3 of water, or 1.3 10^21 kg of water. So you'd need about 1/100000 of the earth ocean of anti-matter to have something comparable to the kinetic energy of venus. Now, of course, 1% will already have an influence, but don't forget that much energy will not go into "orbit changing" but rather in heat and most in intense gamma radiation. You will get a terrible gamma flash, better do this out of sight (or at least put on strong sunglasses).

    So you'd need of the order of a millionth of the earth's ocean of anti-matter do do your feat...
     
  5. Apr 30, 2008 #4

    Gokul43201

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    If the explosion happens close to the surface of venus, then nearly half the gammas will transfer momentum to the planet. A mass on the order of about 10^19 kg will make a momentum transfer on the order of 1% of venus' orbital momentum.
     
    Last edited: Apr 30, 2008
  6. Apr 30, 2008 #5

    Andy Resnick

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    Is the actual plot device the altered orbit of Venus? If so, then you'd be well served to come up with an alternative, as pointed out by others- antimatter won't cut it.

    What if a small black hole goes whinging by? Or a cosmic string sideswipes the planet? Or an Oort cloud/Kuiper belt object comes loose and smacks into Venus?
     
  7. May 1, 2008 #6

    LURCH

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    Alternatively, a friend of mine is currently creating a role-playing game in which a rogue planet passes through the Solar System, dissrupting orbits. If you send one of these through your story, you could have it pass close to Venus when Venus is on the far side of the Sun, and no ither planets are near. This, however, will not give you the cratering or loss of cloud-cover (which I'm guessing might be important to your plot, am I right?).
     
  8. May 1, 2008 #7
    Well that was illuminating.

    Its interesting that a substance that is to be a hundred times more than powerful nuclear fission by weight is somehow "less" in raw power than say a space rock that smacks into the side of an celestial body. At least in terms of effecting momentum. I could certainly imagine the creation of a nuclear weapon so powerful that it could peterb the planets orbit, but i guess by the reasoning here that would be false.

    The main plot device needs to be something that effects the orbit sufficantly and meets a few criteria.

    1. It must be man made, or man-caused.
    2. It must somehow blow enough atmo-shpere off the planet that it becomes more usable. Not habitable mind you, but enough that it brakes the greenhouse effect to more manageable levels and makes the planet worth utilizing by a Type 1.1 or 1.2 Civilization.
    3. This event must have in some way perturbed its orbit in a fashion that requires a massive enginnering effort to eventually correct. It should not be something that results in the death of the planet within say a few months, but could cause problems years down the road.

    Maybe a miscalculated mining asteroid moved incorrectly of sufficant size?
     
    Last edited: May 1, 2008
  9. May 2, 2008 #8

    vanesch

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    Note that you are talking about 10^19 for the momentum balance (I didn't check it, suppose your numbers are right), while I was talking about 10^16 (thousand times less) for the energy balance. 10^19 is 1% of the earth ocean...
     
  10. May 2, 2008 #9

    vanesch

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    Indeed, have a look at the "standard" hypothesis for the K-T boundary extinction (end of the dinosaurs) 65 million years ago: the impact of a meteorite http://en.wikipedia.org/wiki/Alvarez_hypothesis

    The impact is estimated to be energetically equivalent to a few million of the most powerfull thermonuclear weapons ever build (Tsar Bombas), and it didn't significantly change the orbit of the earth.

    Nukes are peanuts compared to celestial bodies (unless they are celestial bodies themselves, such as supernova).
     
    Last edited: May 2, 2008
  11. May 2, 2008 #10
    Even if the explosion is not powerfull enough to directly move a planet, it could do it by changing an orbit of another body which would pass near the planet (and causing it to crash into the planet).
    Here is an idea: a new minor planet is discovered. It has highly eccentric orbit, which comes as close to the Sun as Venus's. It will pass very close to Venus after some years. Scientists see this as an opportunity to perform some experiments, so they send a spacecraft which attaches itself to the minor planet. However some experiments go wrong and the spacecraft explodes, slight changing the minor planet's orbit: just enough that it crashes into Venus...
     
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