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I've been wondering for a while and have seen conflicting results, so I'm asking. "if an asteroid were to hit an extremely earth-like planet, would it cause the most damage when hitting the water, land, or coast? assume conditions of planet to be identical to earth" additionally, what makes this the most devastating?

Assume (an event) large enough to kill 75% of all life on earth within 50 years of collision.

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    $\begingroup$ How big are we talking? For a relatively small asteroid, landing in the middle of a densely populated city will cause the most damage. For a very large asteroid, it won't really matter where it hits, we'll all be screwed anyway. $\endgroup$ – Nuclear Hoagie Feb 12 at 17:29
  • $\begingroup$ assume large enough to kill 75% of all life on earth within 50 years of collision $\endgroup$ – zackit Feb 12 at 17:33
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    $\begingroup$ It's usual to wait 48 hours or so before awarding "best answer" as there is an international community which may not even be awake, but might provide an answer to your liking. $\endgroup$ – Rottweiler on market-day. Feb 12 at 18:01
  • $\begingroup$ Just outside of (so that all the goo gets dispersed and not destroyed) Silicon Valley, or basically anywhere in China where there's a bunch of chemical processing plants. $\endgroup$ – Mazura Feb 13 at 2:51
  • $\begingroup$ this isnt on earth $\endgroup$ – zackit Feb 23 at 13:49
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I've read that the worst place for a Chicxulub class impact (relative to land, sea, or coast) is in shallow water, i.e. continental shelf. Coastal waters, that is.

Why? Because there's water, and there's rock without too much water on top of it.

The rock will be blasted into partial orbits, with the "burning sky" effect (everything on earth will be under an oven broiler for an hour, producing a planet-wide firestorm), dust blasted into the stratosphere (which, combined with soot and ash from the fires, will result in an "asteroid winter" as well as the sulfuric rain mentioned in another answer), and sea water quenching the glowing rock at the actual impact site will cause global cloud cover almost instantly, resulting in flooding, rain to carry the sulfuric acid, massive erosion, and general mayhem.

Deep water shelters the rock below, unless the asteroid involved is much larger than a few kilometers, and land lacks the prompt cloud effects and planetary rains.

From comments, there's also this paper, which suggests that the angle of impact also contributed -- by way, once again, of maximizing the mass of material thrown into and above the atmosphere, as well as its dispersion.

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  • $\begingroup$ Link to relevant paper $\endgroup$ – user2352714 Feb 12 at 18:03
  • $\begingroup$ Thanks, @user2352714 -- it hadn't occurred to me that angle was strongly contributory. $\endgroup$ – Zeiss Ikon Feb 12 at 18:15
  • $\begingroup$ Nice answer, but wrong. Maximum damage to the planet occurs when you punch through the thin crust underlying deep ocean. 6km of oceanic crust is much easier penetrated than 65km of continental plate. Punch a hole in the bottom of the ocean, put the ocean water in contact with the magma below. Over an area of many square kilometers. The resultant steam explosion dwarfs the asteroid's energy by several magnitudes, the then resultant tsunami covers the entire landmass of the planet. Even the high mountains. This is not a 75% killer, this is a 100.00000% killer, down to microbial level. $\endgroup$ – PcMan Feb 12 at 18:43
  • $\begingroup$ @PcMan That looks like an answer. I'd question, however, how big and how fast the impactor needs to be to actually punch through 5 km of rock under a similar amount of water. Bigger/faster than the dinosaur-killer, I think... $\endgroup$ – Zeiss Ikon Feb 12 at 18:58
  • $\begingroup$ Conveniently enough, Chicxulub just so happened to hit in coastal waters... $\endgroup$ – Vikki - formerly Sean Feb 13 at 1:40
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If we talk about damage in general (and not damage to a specific civilization settled in a specific area of the planet) in the short term, I would say that the most devastating location for an asteroid to hit would be an ocean, because of the huge waves and tsunamis that would hit all nearby continents.

However, if we're talking about the long-term consequences, maybe the location is not that important after all. According to recent studies regarding our own planet, the asteroid that killed the dinosaurs caused a rain of sulfuric acid, coming from the sulfur found in the rocks where the asteroid hit. Over time, this acid rain caused the acidification of the oceans and this would have also caused a mass extinction in the marine environment.

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  • $\begingroup$ so hitting in a fairly shallow area of the ocean would likely cause the most devastation? thank you $\endgroup$ – zackit Feb 12 at 17:47
  • $\begingroup$ Remember that not all rocks have enough sulfur to contribute to the problem. The precise details of which rock may matter more than the precise depth. $\endgroup$ – Mary Feb 12 at 23:12

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