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I am trying to figure out the feasibility of using Anti Matter to bombard the surface of a planet from a position in space.

My gut feeling is that its not very feasible. Wouldnt the Anti Matter react with the upper atmosphere and explode up there instead of on the surface?

Could the Anti Matter be successfully contained in something to deliver itself to the surface so it could explode there? Or is dropping/firing such a container from space problematic as the container would heat up and vibrate whilst entering the atmosphere?

My guess is that if you were sufficiently advanced enough to have Anti Matter based weapons, they would only really be effective in space. Using these weapons on a planets surface or anywhere surrounded with matter would have the risk of the weapon going off too early, or even worse, taking you out.

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    $\begingroup$ It really depends on the technology level accessible to the race using antimatter weapons. At current Earth level technology we are happy to create few molecules of antimatter and keep them stable for very short amount of time. So even imagining how such antimatter containment would look like is quite beyond my level of knowledge $\endgroup$ – Pavel Janicek Feb 13 '17 at 11:27
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    $\begingroup$ Orbital Bombardment in itself is a very powerful weapon, combining that with AntiMatter would unnecessarily complicate your attack. What is it that you want to achieve? Crack the Shell, Blow off the atmosphere etc $\endgroup$ – AEonAX Feb 13 '17 at 11:27
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    $\begingroup$ @Jimmery: in orbital bombardment the 'warhead' is the kinetic energy of the bombardment itself: so essentially your delivery mechanism for anything from orbit is going to form part of the destructive power. $\endgroup$ – Joe Bloggs Feb 13 '17 at 12:26
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    $\begingroup$ Just use big rocks, the damage will be immense anyway, and its very simple and reliable. Fly a mission to a nearby asteroid, capture it with a claw, and tow it into a lunar holding orbit... hmm, something sounds familiar... $\endgroup$ – Innovine Feb 13 '17 at 15:55
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    $\begingroup$ @Innovine: Big rocks aren't that cost effective. You'd be better off coating a slug of iron with heatproof ceramic plates and slamming that into the planet. Cheaper, easier to aim, delivers more kinetic energy to the target rather than the atmosphere and you can fine tune the payload size for tactical bombardment if necessary. Not that I've ever had reason to think about the finer points of orbital bombardment... Nosiree.... $\endgroup$ – Joe Bloggs Feb 13 '17 at 16:34
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Lets take a look at destructive power.

Matter-antimatter annihilation yields all of the available resting energy of both the antimatter and the matter it's annihilating. This may be more than you expect. In fact it's at least 43 kilotons per gram. The kinetic energy of the impactor is nothing compared to that. Since your aliens are looking at weaponising this stuff then I'm going to guess they have the capacity to make and handle a lot of it.

So lets assume (for fun) that our aliens are throwing around munitions on the same order of size as a small naval shell, say 500 kg. Each kg is 43 Megatons. You've lobbed enough antimatter into the atmosphere to theoretically yield 21.5 GIGAtons. The Tsar Bomba, largest nuclear bomb ever detonated, was only 57 megatons (1.3 kg), and that had a mushroom cloud that reached above the stratosphere and an 8 kilometre wide fireball. Tsar Bomba's fireball was prevented from reaching the ground by the shockwave it produced (it essentially blew itself back into the sky), but that same shockwave entirely levelled a town 55 km from the blast zone and caused third degree burns at 100km.

So: Do you need containment?

Not really. If you can make enough of this to be viable for use in warfare then you can just aim for the planet and hit go.

As soon as the antimatter hits the atmosphere (which it will be doing really early on, even if the atmosphere is thin) it's basically going to turn into a rocket engine trying to power it's way back up to the stars by blasting all the normal matter below it out of the way. BUT! Unless you skim the shot off the atmosphere then it shouldn't be able to do that until it gets pretty far through the atmosphere. Most of the matter in the atmosphere is concentrated in a layer about 15-18km thick. Remember how big Tsar Bomba was? Even if your munition doesn't get anywhere near the ground it's still going to devastate it.

The advantage to antimatter weapons is that they'll keep exploding until they're completely consumed: Exploding high up in the atmosphere is still exploding: still creating a huge shockwave, and still creating huge problems for everyone below (like blinding people). Essentially you're going to have a Tsar Bomba going off continuously until all the antimatter is used up.

If it doesn't have sufficient time to turn itself around and leave the atmosphere before utterly fragmenting then it's just going to turn into a raging fireball, and it's likely that fragments of it will in fact be propelled downwards by air hitting the projectile from above (as air does have a bad habit of enveloping things), causing the 'explosion' to descend even closer to the ground.

And this is assuming that you didn't already give it enough power to hit the ground: If you've launched it downwards on a steep orbital re-entry path then it will be going fast enough that the outer layers of antimatter won't be able to create enough of a 'burn' to generate any meaningful thrust (due to the fact that it's annihilating it's reaction mass and blasting any further fuel away in an undirected fashion). It will, however, leave a wake of unprecedented destruction behind it on it's way to the ground, whereupon it's going to be surrounded on all sides by matter it can annihilate with.

Other answers have addressed that containment is possible. I'm just going to go out on a limb and say if you've got the ability to make any reasonable amount of antimatter then it really isn't necessary.

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    $\begingroup$ I don't think this is plausible, First hits with regular matter will produce heat until the shell (I assume you put into shell shape) becomes plasma scattering them. Since the heating occurs from the bottom, it will scatter antimatter outwards. Some of it will continue hitting the air around, scorching the upper atmosphere, some (tiny amount) will reach up to your space craft and do damage. Although it will probably end the life on the ground due to extreme X-Ray radiation, I don't believe it will ever touch the ground. $\endgroup$ – Cem Kalyoncu Feb 13 '17 at 19:11
  • $\begingroup$ Containment could allow for it to be more devastating though. If the "shell" survives to impact the planet's surface, then the reaction is starting at the surface, and could significantly damage the planet's crust. In addition to all the direct kinetic and thermal damage from matter-antimatter annihilations, such a disturbance in the crust could cause planetwide earthquakes and volcanic eruptions (assuming a molten core). $\endgroup$ – Doktor J Feb 13 '17 at 19:25
  • $\begingroup$ @DoktorJ: It certainly could, but as others had already said that I thought I'd focus on why you wouldn't need it if you wanted to avoid complexity and could make enough of it. $\endgroup$ – Joe Bloggs Feb 13 '17 at 19:41
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    $\begingroup$ @CemKalyoncu: The shell will indeed become plasma and start to scatter, but so will the matter underneath it, and the matter underneath that, and the shell will rapidly turn into either a 'spike' of antimatter plasma slamming downwards at 30km/s like a supremely effective EFP or it'll leave a trail of fire brighter than the sun with a thermal shockwave that would make Tsar Bomba look like a firecracker. It doesn't have to reach the ground to devastate, is my point. $\endgroup$ – Joe Bloggs Feb 13 '17 at 19:46
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    $\begingroup$ this answer openned my eyes to the realities of anti matter orbital bombardment - even without containment, given enough of a push the warhead would cause significant damage to a planet - and the imagery of an immense exploding fireball descending onto a planets surface is also pretty damn awesome - have a tick $\endgroup$ – Jimmery Feb 13 '17 at 22:13
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Of course it's plausible.

The only thing that's slightly more out there in the realm of science-fiction is where they got the antimatter.

As you know antimatter is identical to ordinary matter in every way except that the particles it is made of have an opposite charge. This means by manipulating magnetic/electric fields it can be effectively contained within a space surrounded by a vacuum because the antimatter particles get repelled to the center of the canister.

Now as you also know, so far we've only been able to successfully contain antimatter for a very short time (about 16 minutes). To be clear though this is not because longer containment is physically impossible, but rather because how to do so properly is a partially unsolved problem of engineering. Importantly we are working on this issue and many believe we are close to solving it. And honestly, if your people can somehow find or create significant quantities of antimatter (enough for a bomb) then they've already solved it.

So what do you do now that you've got some contained antimatter? Well, just launch it from orbit. The electromagnetic field will persist within the atmosphere but will certainly fail when what generates it gets destroyed on impact. When that happens all the antimatter is free to interact with normal matter and... boom. You get a very, very big explosion.

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    $\begingroup$ Note that "dropping it from orbit" really needs to be launching it from orbit with some velocity, or giving the canister some thrust of its own. If you just let it go in orbit, it will keep orbiting with your spacecraft until you do something about it. (luckily you are in space so you don't need to worry too much about it prematurely annihilating) $\endgroup$ – mao47 Feb 13 '17 at 13:10
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    $\begingroup$ @mao47 & Jimmery Good catch, I was going for the figurative sense of drop as in: "drop off the package", but I suppose in response to such a question I should have been more technical. Edited for clarity. $\endgroup$ – AngelPray Feb 13 '17 at 13:17
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    $\begingroup$ I was 2 days ago in the "antimatter factory" at CERN. you can only trap antimatter for about 1000~ seconds. But to bombard a planet you do not need to trap it! The problems at CERN come from being able to have antimatter in vacuum in very low energy states. You want to kill a planet, you do not need to even store antimatter. You can have a cannon that creates antimatter at high energies and these are focused in a direction. That would suffice. $\endgroup$ – Ander Biguri Feb 13 '17 at 13:55
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    $\begingroup$ Antimatter is not just matter with electrical charges reversed, but the subtleties might not be important in your story. See Greg Bear's Anvil of Stars for a planetary defense system that makes creative use of antimatter. $\endgroup$ – Beta Feb 13 '17 at 15:35
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    $\begingroup$ @Sobrique: Even if the canister isn't made of matter and you've fashioned a shell out of an anti-metal then you've still got to be careful about interstellar dust. Even a nanogram of matter touching your projectile will yield an explosive force on the order of a kilo of TNT going off, which should be more than enough to shatter the projectile. Not an issue if you're firing at short range but really, really important if you're aiming for anything longer. $\endgroup$ – Joe Bloggs Feb 13 '17 at 16:26
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Antiprotons can be trapped in electromagnetic field. Since your bombs will be quite small, with the right materials, atmospheric entry of small shells will be possible. Find a way to trigger bombs when they hit the surface, and you will be done. That is easier than regular shells, once electromagnetic field is gone, antimatter will eat through the outer shell.

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Based on your initial description, it sounds like you are sending "naked" antimatter" to the planet, and yes, it will interact in the upper atmosphere.

Of course, this isn't going to be much of a help to the people below, positrons will interact with electrons releasing gamma rays at a distinct 512 KEv energy (anyone outside the battle zone picking up the signature will have no doubt at all what just happened), while anti protons will interact with protons releasing a blast of high energy subatomic particles. As you can see in the diagram of a theoretical antimatter rocket, this stew of pions and other charged particles breaks down in time to other particles as well as releasing gamma radiation.

enter image description here

Antimatter reaction

So the surface would be struck with a blaze of high energy radiation, followed shortly by the shockwave created by the atmosphere heating by the radiation release.

This would also affect everyone in space, since the radiation release would be spherical. Satellites and spacecraft in orbit would be irradiated by the high energy gamma rays and particles as well, which might even put the launching spacecraft in danger.

The best way to overcome these issues would be to enclose the antimatter in a containment trap which is programmed or designed to disintegrate at low altitude or on the ground, putting the energy right on the target where you want it to go.

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  • $\begingroup$ Good point about blowback radiation! $\endgroup$ – Joe Bloggs Feb 13 '17 at 18:29
  • $\begingroup$ Not to mention, the containment trap conveniently allows for the atmosphere now above the reaction to contain the it and (to a limited extent at least) dampen radiation. $\endgroup$ – Doktor J Feb 13 '17 at 19:28
  • $\begingroup$ this is a fantastic answer - I wish I could award the tick to more than one answer - thanks for the insight into the radiation resulting from a anti matter explosion $\endgroup$ – Jimmery Feb 13 '17 at 22:10
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As you have already commented the most effective way would be the ion trap. The two most common types of ion trap are the Penning trap and the Paul trap. A possible alternative could be the use of Optical tweezers, but this method can not contain the antimatter for a long time.

Also you have to take into account that there are different types of antimatter, you cannot define everything with the term antimatter and expect to treat it equally. Neutral antimatter is a different type of antimatter, which is not affected in the same way by ionic traps. Last but not least, you have to keep in mind that it is not yet known how antimatter is affected by gravity and that could be a big problem for your bomb.

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  • $\begingroup$ As far as i am aware it is completely known how antimatter is affected by gravity; as in the same as normal matter. Antimatter just means particles with opposite electrical charge (electron+ = positron), all other properties being identical $\endgroup$ – AZ. Feb 13 '17 at 13:19
  • $\begingroup$ Sorry but this is not true, if antiparticles or antimatter move in the opposite direction to ordinary matter (for the opposite electrical charge) in a gravitational field, the Principle of equivalence and with it to the general theory of relativity would be overturned. $\endgroup$ – Gawey Feb 13 '17 at 13:29
  • $\begingroup$ We now know that gravity affects antimatter, but we do not know how it affects. For more information look for experiments carried out on the CERN. $\endgroup$ – Gawey Feb 13 '17 at 13:34
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    $\begingroup$ To quote wikipedia: "The gravitational interaction of antimatter with matter or antimatter has not been conclusively observed by physicists. While the consensus among physicists is that gravity will attract both matter and antimatter at the same rate that matter attracts matter, there is a strong desire to confirm this experimentally." $\endgroup$ – Joe Bloggs Feb 13 '17 at 16:31
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It depends what you want your bombardment to accomplish.

Can you technobabble up an explanation for delivering antimatter from space to a planet's surface? Sure, that's just Star Trek's photon torpedoes. It's likely to be very unpleasant for any inhabitants. and will scar up the surface.

Can you fire raw antimatter directly at the planet? Sure. It will react with the atmosphere in spectacular ways, and the fallout will be unpleasant for any inhabitants, but the surface may not be strongly affected (depends how much antimatter you use).

Can you fire raw antimatter at relativistic speeds so it makes it down to the surface? Sure, probably. You must really hate those guys. I don't even know how to estimate what that might do, but it will be unpleasant for any inhabitants and probably scar up the surface (depending how relativistic the speeds are).

Can you use your antimatter in an engine to just drop rocks on the surface? Sure, anything massive enough to survive reentry has some nasty bombardment characteristics (Heinlein overestimated, but Pournelle didn't). Following the theme, it will be unpleasant for any inhabitants, and probably scar up the surface.

In general though, you aren't going to achieve any non-exterminatory objective with antimatter. Figure out what you're trying to do, and do that instead of focusing on the loudest toys.

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    $\begingroup$ Relativistic antimatter is redundant. At 86% the speed of light, the kinetic energy of the projectile is equal to its mass energy. Get it going faster, and the little bit of "bang" from being made of antimatter will be dwarfed by the big "bang" of the impact. $\endgroup$ – Mark Feb 13 '17 at 21:53
  • $\begingroup$ @Mark, the question wasn't size of the bang, but whether you can make the bang occur on the surface. Aside from that constraint, I agree: the "relativistic" part rapidly gets more exciting than the "antimatter" part. $\endgroup$ – fectin Feb 13 '17 at 22:36
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The major problem with an anti-matter kinetic energy weapon is that it will act exactly like a meteor. You surely have seen the wonderful sights we have when we get meteor showers like the Leonids?

Unless the anti-matter is protected by a containment field which fails automatically when it reaches the surface, you are going to have your anti-matter KEW disintegrating when it hits every matter atom in its path on its route to the surface. When enough matter particles interact with your anti-matter weapon, it's going to disintegrate. If it's a large enough chunk of the local asteroid belt, it's going to have a worldwide killing effect.

One possibility is that the spaceship and crew are matter and the planet is anti-matter. Nobody thought to check that possibility, so you get disastrous gamma radiation affecting both the planet and spaceship.

Sending down an exploratory vessel, perhaps with a diplomat or two, and having it disintegrate in the atmosphere of an anti-matter (to them) planet is not the best way to start diplomatic negotiations. The planet may think it was a weapon. The spaceship knows it was an accident but has no way to prove it. Voila! Instant interstellar war. Any linguistic team would probably include scientists -- physicists, chemists, mathematicians, and other natural sciences -- since that would be the easiest way to establish common words. The properties of carbon and oxygen don't change from one world to another. But if the best diplomats and scientists you have with you have just been killed in this matter-anti-matter, you have a major problem.

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