Relativistic Kinetic Projectile Help

fsci123

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I am working on a scifi movie and i am wondering what will a hit from a 200,000 metric ton projectile of various composition look like. One of the projectiles will be made of tungsten... One of the projectiles will be made of Depleted Uranium... One of the projectiles will be filled with pellets of fusion fuel...

What will happen when these projectiles hit a planet with and without an atmosphere. Could the projectiles be seeded with radioactive materials?

These are traveling around 0.72c
 
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jedidia

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what will a hit from a 200,000 metric ton projectile of various composition look like.

It depends on their speed, really, but since the thread title includes "relativistic", it would look like a white flash no matter the composition. Because whatever the composition, the projectile will break down to at least atomic particles on impact.

Also, 200,000 tons is a hell of a lot of mass to come flying at relativistic speed. Just flipping it over in my head, at 0.9 c that should be around 5.8e9 MT (about 5.8 billion mega-tons, in case you think I wrote that number wrong) of TNT. That should be enough for some six to seven [ame="http://en.wikipedia.org/wiki/Wilkes_Land_crater"]Wilkes craters[/ame]

The impact would certainly look spectacular, very bright (i.e. white to the naked eye) and should be visible a few solar systems away. The composition of the projectile certainly won't figure in what the flash looks like (unless you're looking at its residue through a spectrometer from a few ligtyears away, maybe).

Seriously, I think you should make the projectile less massive... ;)

What will happen when these projectiles hit a planet with and without an atmosphere.

You wouldn't be able to discern anything unless you're watching the whole thing in ultra-bullet time. It's happening too fast. Presumably there would be a very devastating shockwave propagated through the atmosphere leveling pretty much every building on the planet (like a tsunamy, only that this time the wave is hot air instead of water), but most of the energy should still be absorbed by the body itself, which might completely tear up less dense bodies (not the earth, though). But even if the earth wouldn't fly to bits, you can bet that the resulting earthquake literally won't let a stone stand on the other on the whole planet. You'll have a very prominent landmark the size of a small continent on impact, some new mountains, probably a lot of older mountains gone, and I wouldn't be surprised if the even initiated a new continental shift.

I can't calculate by how much the crust would heat up, but it would be measurable (wich is scary enough).

Could the projectiles be seeded with radioactive materials?

Of course they could, but it would be utterly pointless. As I said, the projectile and the immediate surrounding of the impact would come appart at the atomic level. I think there would be quite some X-ray release, probably neutrons, and the whole impact area would glow green for quite a while...
 
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MaverickSawyer

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Try about 2 tons and at orbital velocity, and use the formula E=1/2mv^2. Result: about 12KT equivalent. In other words, ouch time! Using 200000 tons at fractional c velocities is enough to destroy a planet.
 

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Well, 200 000 tons is something like a large starship may mass. Suppose a scenario where some sort of engine failure or deliberate sabotage prevent it from slowing down and you could come up with a plausible scenario where it could impact planet.
At 0.9 c impact there would be lots of radioactvie fallout because individual particle energies of impactor would be more than enough to cause transmutations and irradiate the surroundings, but that wouldn't matter anyway since anyone who isn't inside super hardened bunker would die from blast effects.
 

Linguofreak

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Using 200000 tons at fractional c velocities is enough to destroy a planet.

Not even close, unless your velocity is very high. At 0.86c (where a projectile's kinetic energy equals its rest mass), you're still about 7 orders of magnitude short of the gravitational binding energy of earth. The KE of a 200000 ton projectile at that speed is on the order of 10^25 joules. You need around 6x10^32 to destroy the earth. You need a speed with about 15 nines after the decimal point (0.999...9c) to destroy the earth with a 200000 ton projectile.

At 0.86c, you couldn't even boil off Earth's oceans with the impact energy (that would take on the order of 10^27 joules). That said, you would release around 30 times the energy of the Chicxulub impact...
 

ED_4

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Not even close, unless your velocity is very high. At 0.86c (where a projectile's kinetic energy equals its rest mass), you're still about 7 orders of magnitude short of the gravitational binding energy of earth. The KE of a 200000 ton projectile at that speed is on the order of 10^25 joules. You need around 6x10^32 to destroy the earth. You need a speed with about 15 nines after the decimal point (0.999...9c) to destroy the earth with a 200000 ton projectile.

At 0.86c, you couldn't even boil off Earth's oceans with the impact energy (that would take on the order of 10^27 joules). That said, you would release around 30 times the energy of the Chicxulub impact...

It might not destroy the planet. But it sure will destroy slowly the living things on it with a sure event of an ice age happening. :jawdrops:
 

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One of the projectiles will be filled with pellets of fusion fuel...

This won't really be very helpful unless the velocity is fairly low. At 0.12c, the yield from kinetic energy is about equal to that from fusing the entire mass of your projectile from hydrogen-1 to helium-4 (in practice, you'd be using a deuterium/tritium or deuterium/helium-3 mix, which would have around 2/3 of that yield per unit mass). So at any speed significantly greater than 0.12c, the impact yield will greatly exceed the fusion yield, and you may as well not bother.

At 0.86c, your impact yield is equivalent to the yield from your projectile being half antimatter by mass (assuming that the matter and antimatter portions mix thoroughly enough to annihilate completely). At 0.94c, your impact yield is equivalent to the projectile being 100% antimatter by mass (assuming a target made of matter and thorough mixing). In other words, if you go much beyond 0.94c, you won't significantly increase the yield even by building your projectile completely out of antimatter. (That said, giving your projectile that kind of kinetic energy will require significant amounts of antimatter, or the fusion of even more significant amounts of hydrogen into helium).
 

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Forget projectiles. Just use a Deathstar! The huge beam that comes out of it will be the end of the planet. End of discussion. :thumbup::lol:
 

Linguofreak

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The impact would certainly look spectacular, very bright (i.e. white to the naked eye) and should be visible a few solar systems away.

Well, the color would be that of blackbody radiation at the temperature of the debris: bluish-white at first, fading through to red as the debris cooled.

The composition of the projectile certainly won't figure in what the flash looks like (unless you're looking at its residue through a spectrometer from a few ligtyears away, maybe).

Even then, I'd think that the composition of the target would likely determine what you'd see: you're going to have a whole lot more debris from the target than from the impactor.

You wouldn't be able to discern anything unless you're watching the whole thing in ultra-bullet time.

True of the impact itself. The "molten debris from the target flying all over the place" part would last for minutes or hours (days even, if the impact velocity (and corresponding impact energy) were high enough).

Of course they could, but it would be utterly pointless. As I said, the projectile and the immediate surrounding of the impact would come appart at the atomic level. I think there would be quite some X-ray release, probably neutrons, and the whole impact area would glow green for quite a while...

Probably not, actually. Not because material in the impact area wouldn't be irradiated, but because most of it would probably cease to be in the impact area. I imagine that it would leave a distinct mark in the planet-wide geological record as far as isotope ratios, etc, though.
 

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it might not be enough to boil the ocean, but it sure will be enough to heat it up so much that most of the living creatures there would die, and of course, a part of the atmosphere some thousands of kilometers in the vicinity would be lit up
 
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