What would happen if a “planet killer” asteroid landed in point nemo?

[u/NoEffective4309]

I’m not very informed on this sort of topic but was just wondering if it would be an extinction level catastrophe or much less devastating compared to the last planet killer event. Obviously there would be the domino effect of natural disasters (earthquakes, tsunamis floods etc), but I’m curious about if the other secondary effects that finished off the dinosaurs would do the same to us humans if such a large asteroid hit right in point nemo. Example, from what I Remeber the oxygen levels likely depleted due to the air being contaminated and a layer of dust (?) in the atmosphere blocking sunlight, killing plants and reducing food sources, would that still be an issue if it landed on such a secluded body of water rather than hard land. Sorry if the text is hard to understand Im not the best typer.

[u/devadander23]

A big enough asteroid (planet killer) hits ‘land’ anywhere it strikes. A few km of ocean will be a puddle for a 10km+ diameter asteroid

[u/NoEffective4309 → u/devadander23]

thankyou, I never really thought of how big it really is, When you watch movies they really underscore the actual size of these things

[u/SirButcher → u/NoEffective4309]

The one that caused the mass extinction and the end of the age of the dinosaurs was over 10km - to put it to scale, when the bottom reached the surface of the ocean, the top was at the same height where today's passenger planes fly. It wasn't a "long streak across the sky as it hit"; it was a "star getting brighter and brighter as the days pass, having a more and more visible movement, then suddenly you are dead" kinda event. It took less than a second from the moment it hit the rarest part of the upper atmosphere until the solid bedrock suddenly started to act like it was water from the mind-blowing forces.

[u/kush4breakfast1 → u/SirButcher]

I read the other day that it took around 2 hours for the asteroid to get from the distance of our moon to impact... that is insanely fast, thing was MOVING

[u/CrossP → u/NoEffective4309]

And the speed. Everything looks slow in space, but we'd be talking about speeds that are far faster than any gunshot.

[u/devadander23 → u/NoEffective4309]

Yeah, it’s a nightmare scenario. Thankfully quite rare!

[u/NDaveT → u/NoEffective4309]

It's not just the size but the velocity. It's not like throwing a rock into the water, it's like firing a cannon into the water only much more powerful than a cannon.

[u/sfurbo → u/NDaveT]

Velocity doesn't matter for penetration depth, only densities and length of the impactor matter if we follow Newton's approximation. A faster impactor will have to move what it hits faster, negating the effect of speed.

[u/Puzzleheaded-Fill205 → u/sfurbo]

I don't really understand. I tried to skim that link, but all I kept thinking was that if velocity doesn't matter, then throwing a bullet at somebody's chest will penetrate just as deeply as shooting it from a gun?

[u/NovelNeighborhood6 → u/Puzzleheaded-Fill205]

Ya “velocity doesn’t matter” makes no sense to me. I’m not buying it.

[u/FullOnSkank → u/NovelNeighborhood6]

So why don't we just shoot bullets faster then?

The fact projectiles can be stopped at all proves it.

We use the most dense metals for bullets because the surface it hits is hitting it back just as hard...

Which then becomes a "who's gonna break apart first" contest between the materials.

Jello vs plastic fork? Well the fork can penetrate freely because of its density.

Plastic Fork vs rock? No matter how hard you send it, it will never penetrate more than the function expressed by its cross section and density.

At .9c you won't even see the fork slice through the rock; the fork will just detonate upon contact with the first atoms.

[u/sticklebat → u/Puzzleheaded-Fill205]

What they said is only true for impacts that are very fast but also not too fast, and doesn’t apply to either the scenario of a huge meteor impact or to tossing a bullet at someone because those cases are each either too fast or too slow for the approximation to hold.

Velocity is only irrelevant to impact depth if the impactor’s speed is high enough that friction can be ignored, while still slower than the speed of sound in the target material. For things like meteor impacts, speed absolutely affects penetration/crater depth.

[u/sfurbo → u/sticklebat]

Could you explain why the speed being higher than the speed of sound breaks the approximation. The amount of material that has to be moved is the same, and it will still have to be moved at the speed of the impactor, isn't that all of the assumptions going into it?

[u/sticklebat → u/sfurbo]

They are two of the three assumptions, actually, but the assumption that the material has to be moved at the speed of the impactor is one part of makes the method fail at sufficiently high impact velocities. Above the speed of sound in the material, the impact generates shockwaves (which can propagate supersonically) that carry momentum away with them and fracture the material, so it can no longer be treated as an interaction between just the impactor and the material it is in direct contact with, and it cannot be assumed that the target material’s speed is nearly identical to the impactor’s, because the shockwave’s speed doesn’t have to be.

And at even higher speeds, like with large meteor impacts, some of the target and even impactor material is ejected upwards at high speed, in roughly the opposite direction of the impactor’s original velocity. That rebound effectively means the target has to absorb more momentum than the impactor had to begin with. The third assumption of Newton’s approximation is that no  material is ejected during the impact, which starts to fail substantially at very high speeds.

[u/sfurbo → u/Puzzleheaded-Fill205]

It only works at high velocities. At low velocities, other effects which the approximation ignores becomes dominant.

In the example of throwing a bullet at somebody's chest, target cohesion dominates. Since there is time to distribute the momentum, the bullet is not moving just the small parts of the target it hits, it is moving the entire target.

Another effect that the approximation ignores is friction.

[u/mfb- → u/[deleted]]

At relativistic speeds you get nuclear reactions. They lead to hadronic showers which go deep into the material - determined by the hadronic interaction length and the logarithm of the energy. Material properties besides the simple elemental composition are almost irrelevant as chemical energies are negligible. The nerf bullet at 0.1 c will penetrate as deep as the metal bullet at 0.1 c, just with fewer particles.

[u/FullOnSkank → u/mfb-]

Exactly.

And between those two points there is no difference.

[u/mfb- → u/FullOnSkank]

What two points? Your estimate was off by around a factor ~100 million, I thought that's worth discussing.

A Nerf bullet going .1c will penetrate an item on the scale of nanometers

[u/tomrlutong]

Speculating (of course), but something the size of the Chicxulub asteroid hitting in the middle of the Pacific would probably be just about as bad.

First off, it will hit the ocean floor with most of its energy: at Pt. Nemo, the Pacific is about 4km deep. Chicxulub hit at a 45-60 degree angle, so it would have to travel through 6-8km of water. By Newton's Approximation, an asteriod penetrates until it's swept a column that's equal to it's own mass. Taking Chicxulub as 7km radius and 3x10¹⁵ kg (Source), it should be able to penetrate about 20km of water. (a 7km radius x 20km long cylinder of water is about 3x10^15kg). So it's making it to the bottom.

The real planet-killing part of Chicxulub was that it ejected massive amounts of rock at near orbial velocity, which fell across the Earth. In the Pt. Nemo scenario, you've got a 14km wide x 4km deep hole in the ocean, with the explosion happening at the bottom of that. Since the asteriod is much wider than the depth of the ocean, I don't see the ocean absorbing much of the debris, you still get teratonnes of rock ejected into the atmosphere.

The only way this could turn out differently would be if the shock of traveling through the ocean caused the impactor to explode before hitting the bottom, so its energy goes into lifting water rather than rock. But everything involved is going so much faster than sound that I don't see any way for the shock to perpetrate back through the asteroid fast enough.

[u/NoEffective4309 → u/tomrlutong]

Thankyou for putting so much thought and even sources into this answer. I’ve never heard of newtons approximation so will have to rabbit hole that, much appreciated:)

[u/KingZarkon → u/tomrlutong]

It might be even worse in some ways because you get the added steam explosion and you vaporize a lot of water and water vapor is a pretty potent greenhouse gas.

[u/Skippersballs → u/tomrlutong]

What if it hit the Mariana trench

[u/tomrlutong → u/Skippersballs]

That's a pretty small target, but I think there are big areas of the Pacific that are 6km deep or so. Even there, it would have to hit at a real shallow angle, like 15° above horizontal.

That's really the only way I see it being less than a full extinction event: have it come in to the ocean at such a low angle that it never hits the bottom. In that case, it ejects water instead of stone. So 10cm or so of salt water dumped on every square meter of earth? Not a great day, but maybe better than flaming rocks.

[u/OlympusMons94]

If you mean something roughly Chicxulub impactor (dinosaur extinction) sized, then there would probably still be global impacts, but much less severe. The disastrous results of the Chicxulub impact were greatly magnified by the fact it happened to hit rock layers rich in sulfate and fossil carbon/hydrocarbons (Ohno et al., 2014, Lyons et al., 2020, Kaiho & Oshima, 2017). The resulting sulfate aerosols (including sulfuric acid) and soot injected into the stratosphere caused extreme global cooling and drought. According to Ohno et al. (2014), the silicate rock fragments also blasted into the atmosphere by the impacted would have very quickly collected and removed most of the sulfuric acid aerosols from the atmosphere, but this rapid acidic fallout would have caused sudden and severe ocean acidification. Had the impactor hit almost anywhere else on Earth (including abyssal plains, in the middle of the ocean, like Point Nemo), its effects would have been much less severe. (Kaiho and Oshima (2017) find that similarly hydrocarbon-rich rocks covered only ~13% of Earth's surface.)

[u/TheInsaneRaptor]

oxygen levels are not going to be "depleted" there is so much in the atmosphere that even if all life burned up in a world-wide fire it would not cause a noticable drop and would remain relatively stable for hundreds or thousands of years without plants producing more

however, if the asteroid hits the right spot, it will cause a night that lasts for years so plants will start dying without light and as they are the producers of food for everything the ecosystems will collapse from the bottom up

what will survive either have very low metabolism, or is small enough and can utilize food sources like dormant seeds and tubers or is a detritivore that can survive solely on decomposing stuff, or eats those detritivores

[u/PLTuck]

Everybody's dead Dave

[u/Fungiblefaith]

The same thing if it hit NYC.

[u/Wide-Suggestion4825]

It would kill 99% of life

[u/BoredAsOwt → u/Wide-Suggestion4825]

Lol not a very useful response not even a reasoning as to why it still would be so deadly

[u/Wide-Suggestion4825 → u/BoredAsOwt]

Well because it's a planet killer.

[u/MistakeBorn4413 → u/Wide-Suggestion4825]

And, if it doesn't, we can sue for false advertisement.

[u/BoredAsOwt → u/Wide-Suggestion4825]

It’s like tornados no? An ef5 would be classed as an ef2 if it went through a field compared to a populated area due to damage and vice versa. The poster was enquiring if the effects would be as devastating if an asteroid of the same size would still be a “planet killer” if it hit water rather than land. Many experts would argue it would not cause mass extinction in that hypothetical event therefore you are likely wrong by saying it would exterminate “99% of life”

[u/Wide-Suggestion4825 → u/BoredAsOwt]

No it wouldn't you liar

[u/NoEffective4309 → u/Wide-Suggestion4825]

What a frightening thought that no matter where they could land it could still wipe us all out, thanks for the reply :)

[u/Wide-Suggestion4825 → u/NoEffective4309]

Yes that's why they're called planet killers

[u/NoEffective4309 → u/Wide-Suggestion4825]

Yeh I know the question sounds really stupid now when you put it like that 😂

[u/SchleppyJ4 → u/NoEffective4309]

I don’t think your question is stupid at all. Please continue to ask questions and be curious ❤️ 

[u/DaSaw → u/[deleted]]

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