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For my world, a planet sends a high amount of magnetically confined antimatter towards another planet the size of Earth and obliterates it. I'm wondering if this would be possible and what effect it would have on the planet.

The Technology is highly advanced and we'll assume that they have the energy required.

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  • $\begingroup$ We've created antimatter on earth and everything's worked out fine. $\endgroup$ – sphennings Jun 5 '17 at 15:49
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    $\begingroup$ Please add more detail - the mass of the antimatter is critical to answering the question. We are currently capable of making small amounts of antimatter and magnetically confining it. A large enough chunk could certainly be destructive to a planet, but at what energy budget and technology level? $\endgroup$ – Isaac Kotlicky Jun 5 '17 at 15:52
  • $\begingroup$ "I'm wondering if this would be possible" Only with properly calibrated dilithium crystals... :) $\endgroup$ – Isaac Kotlicky Jun 5 '17 at 15:53
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    $\begingroup$ "Angels and Demons" on planetary scale :) $\endgroup$ – Alexander Jun 5 '17 at 18:07
  • $\begingroup$ Obligatory XKCD... what-if.xkcd.com/114 $\endgroup$ – CaM Jun 5 '17 at 20:27
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Obliterating a planet isn't easy to do. In fact, using the closest thing the real universe could come to the Death Star weapon, the Nicoll-Dyson Beam, you'd be hard pressed to actually destroy the planet, just wreck the surface and all life on it.

That said, you could certainly use antimatter as a bomb. Containing antimatter is actually the challenge, not detonating it (where nuclear weapons are complex to detonate). So to detonate it on a planet like earth, with an atmosphere, all you need to do is break the vacuum in which the antimatter is contained (magnetics keep it from touching the container, vacuum keeps air or other matter from getting in).

The problems are all proportions, though. While antimatter is a 1:1 energy conversion, and thus very destructive, it actually isn't as advantageous as a weapon as it's easy to think. The biggest problem is that it's EXTREMELY costly in time and resources, to produce. Currently, the only way to produce it is with a gigantic supercollider (such as CERN's LHC), and even then, it's in such tiny amounts that it's not really viable to weaponize.

Assuming your scenario has somehow bypassed this, and large quantities of antimatter can be produced in a "cost effective" manner, it's going to have about the same effect as a nuclear weapon of the same explosive magnitude. It would just take less antimatter to achieve the blast, compared to its nuclear equivalent.

The radioactive ramifications would actually be worse, with tremendous gamma bursts produced.

As for obliterating a planet with this ... like I said, it's hard to destroy a planet. This one survived a mars-sized planet smashing into it (and forming the moon). It would physically survive the sun going nova, by the reckoning of many scientists.

You would need an antimatter weapon with a payload equivalent to at least a quarter of the earth's mass, and you'd have to drive it into the earth a fair distance, before detonating it, or you'd just blast a chunk off the planet, in a spectacular, life-ending apocalypse that ... would still leave a now molten planet there to reform.

COULD this be done? Yes. Is it the most efficient or effective way to mess a planet up? No, that honour goes to the RKM (relativistic kill missile), which is so practical we could technically do it now.

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  • $\begingroup$ If you want to utterly destroy a planet (which is unnecessary if you've destroyed the crust to a level nothing can survive), the only effective way known to do this is to cause the planet to exceed the Roche limit (where something is too close to an equal or greater mass, breaking it up). Saturn's rings are likely the result of a moon falling victim to this. But, good luck creating or moving a sufficient mass to a place where this would happen. A black hole would be surprisingly poor for this even. $\endgroup$ – Cereza Jun 5 '17 at 16:30
  • $\begingroup$ Relativity trumps antimatter! The protons at the LHC have the energy of 17 rest-mass, so using a matter/anti-matter beam pair would not make much of a difference. $\endgroup$ – JDługosz Jun 5 '17 at 20:12
  • $\begingroup$ Yeah, there is that too. Pretty much anything with mass propelled to relativistic speeds becomes death. $\endgroup$ – Cereza Jun 5 '17 at 20:18
  • $\begingroup$ Don't Know where you got the 1/4 figure, but you don't need anything like that much antimatter. Antimatter is billions of times more explosive than rocket fuel, rockets just take off with lots of fuel. Therefore you need 1/1'000'000'000 th of the earths weight. $\endgroup$ – Donald Hobson Jul 20 '17 at 21:50
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According to the accepted answer on this question, the amount of energy required to obliterate an Earth-sized planet is at least 2.4E32J (that's 240 million yottajoules). Conveniently, the same answer also mentions how big your antimatter bomb would have to be to generate that much energy:

2.4E32J is roughly equivalent to... 1.3 trillion tonnes of antimatter hitting the same amount of regular matter.

I think it goes without saying that that's a lot of antimatter. It's a lot of anything. I don't know the density of antimatter (and presumably, different antiparticles have different densities) but let's assume for simplicity's sake it's the same density as your average asteroid. Your bomb will be about a kilometre in diameter. Never mind how you're going to produce all that antimatter and gather it together, how are you going to move it? Then of course, there's the size of the magnetic field that would be required to hold all that antimatter in. You've said they have the energy required to sustain it, but that's still going to be an enormous amount of energy.

Of course, your bomb is going to completely annihilate a chunk of the planet and its atmosphere, equal to its own mass, before the resulting explosion even occurs. But as @Donald Hobson points out in the comments, that's not going to reduce the planet's mass by anywhere near enough to affect the required binding energy.

In short: it would probably be possible with advanced enough technology, but considering how much time, effort, and energy it would take, you'd be better off just making a giant chunk of iron and launching that at the planet at relativistic speed.

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    $\begingroup$ There's also the fact that tectonically-active planets like our own aren't rigid bodies (which would be easier to annihilate). Blasting the crust off a planet isn't that hard to do, but the remainder would endure. Gooey mantle stuff. $\endgroup$ – Cereza Jun 5 '17 at 16:26
  • $\begingroup$ 1.3 trillion tonnes is 1 billionth of the earths mass. The amount lost by annihilation is irrelevant $\endgroup$ – Donald Hobson Jul 20 '17 at 21:51
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You'd need a planet sized lump of Antimatter to destroy a planet completely and if it was all in one lump you'd miss chunks, probably quite a bit of the planet actually, as they got blasted away from ground zero. As to what would happen to a planet hit by a relatively small amount of Antimatter; the Matter/Antimatter reaction is total but not clean, you liberate energy at a rate of 89.9 petajoules per kilogram of reactants most of it as light and heat, but a large fraction is hard radiation which is going to sterilise a huge chunk of space.

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  • $\begingroup$ You can't remove a planet with it, but that's still a really big bomb. A single kg of antimatter releases more energy than 1000 of the bombs that destroyed Nagasaki. I speculate that might alter the climate sufficiently to eliminate all life there, if that is the goal. $\endgroup$ – papidave Jul 20 '17 at 19:42
  • $\begingroup$ @papidave it would more than eliminate life on that world, half a kg of antimatter would probably release enough hard radiation to sterile and surface melt the facing hemisphere of the moon and possibly burn planets farther out. You could completely total a planet you just need several dozen warheads in tight formation hitting at the same time from different directions, and a planet worth of antimatter all up, and the radiation output would sterile star systems that had never heard of you. $\endgroup$ – Ash Jul 27 '17 at 12:50

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