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A challenge with interstellar travel is carrying enough matter to slow down from a significant fraction of light speed. If instead you simply crashed into a planet, it would mean many orders of magnitude less energy needed. Obviously having a craft and payload that can survive the crash is no small problem to solve, but if it was at all possible, it would certainly be preferred by advanced civilizations trying to preserve resources, though only for a use case of extremely rigid payloads. Perhaps delivering 'stone' tablets etched with information (directions to their star system, a theory of everything) being one use case.

So my question is two part:

  1. Could a planet be used to slow down a craft from a significant fraction the speed of light?
  2. Could any matter survive and maintain shape from a crash happening at a significant fraction the speed of light?

Edit: Assuming 10kg at 10% the speed of light, I have calculated 4493776539 MJ of energy. Is this fundamentally impossible for matter to hold any shape or preserve any information at this much energy?

Goose
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    Macroscopic objects traveling at significant fractions of the speed of light are troublesome when not in a vacuum relativistic baseball – Triatticus Jan 23 '23 at 18:42
  • @Triatticus I have read that before, classic. Here I am making an assumption that the material science problem would be easier for a type 3 civilization to solve than the fundamental tyranny of the rocket equation. – Goose Jan 23 '23 at 18:45
  • Seems like a clear declaration of war with a sneak attack on the planet... Masses moving at significant fractions of the speed of light would yield, well, a whole lot of energy... – Jon Custer Jan 23 '23 at 18:54
  • To be fair what most likely got you to light speed is probably your best bet at slowing down too, I suspect that any large object hitting at planet at significant relativistic speeds is unlikely to survive without some sort of sci-fi invention. Not to mention any crew will not survive the deceleration at all. Unfortunately this is likely better destined for world building where you can extrapolate neat ways to do this while trying to stay semi true to reasonable physical models. – Triatticus Jan 23 '23 at 18:55
  • @JonCuster If the payload was only a ton, and was launched into Jupiter, I assume Jupiter (and Earth) would be largely fine and that humans would be thrilled about the interstellar information package. – Goose Jan 23 '23 at 18:58
  • @Triatticus The assumption is it was 'launched' to get to speed (mass driver, controlled explosion). As mentioned this would only be to launch rigid payloads, no crew obviously. The big question is could any matter in theory survive such a high energy event. – Goose Jan 23 '23 at 19:01
  • What leads you to make the assumption that it wouldn't burn-up in entering Jupiter's atmosphere? (As per the xkcd link). Have you done the maths of the energies involved? – Jiminy Cricket. Jan 23 '23 at 19:08
  • @JiminyCricket. I'm aware that any common matter would be vaporized. But does material science leave open the possibility of anything capable of surviving such high energy? Assuming 10kg at 10% the speed of light, I have 4493776539 MJ of energy. Is this fundamentally impossible for matter to hold any shape or preserve any information at this high of energy? I've edited this into my question. – Goose Jan 23 '23 at 19:20
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    At a big enough fraction of light speed, who's to say you won't go straight through the planet? – user253751 Jan 23 '23 at 20:29
  • If humans are on the spacecraft, tell them to jump just before impact! – James Jan 23 '23 at 20:56
  • @user253751: Not sure if you're joking, but you definitely wouldn't go straight through. All the planet material that would have to be displaced by your craft would have a huge amount of inertia and wouldn't move out of your way without a fight. – James Jan 23 '23 at 21:10
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    BTW, your KE value is a bit low. You should use the relativistic equation, $E_K=(\gamma-1)mc^2$, which gives ~4.52776255e15 J. See https://physics.stackexchange.com/a/595175/123208 for details. – PM 2Ring Jan 23 '23 at 21:46
  • That KE is equivalent to ~50.378 g of mass. By comparison, the Little Boy bomb dropped on Hiroshima converted ~0.7 g of uranium to KE, heat, etc. – PM 2Ring Jan 23 '23 at 22:02

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