Why Are Most Impact Craters Perfectly Circular? (Rather than Ovals)

[@theCodyReeder]

Dynamite was once used to blow a beached whale out to sea. Unfortunately even though the dynamite was place on the side opposite the ocean the rotting flesh went all over the place including onto a nearby town. What went wrong? Turns out whale blasting and crater formation have similar physics. ;)

[@scottmanley]

High energy events have a habit of becoming omnidirectional.

[@petlahk4119]

So, were rockets initially developed to push whales out to sea without the whole "aquatic mammal flesh ejecta" problem? :P

[@gasdive]

Ideally whales entering planetary atmospheres should be turned into a bowl of petunias prior to impact.

[@ExaltedDuck]

@@gasdive that seems highly improbable

[@gasdive]

@@joer8854 You're clearly the kinda dude who knows where his towel is at.

[@AttilaAsztalos]

So basically, craters are round because they're no so much the literal indentation matching the impacting object but rather the frozen snapshot of the circularly expanding shockwave it generated...?

[@scottmanley]

I wish I'd had your help writing the script.

[@mduckernz]

Another way of putting it might be to emphasize the relative volumes. The explosion volume is much larger than the impactor, being plasma and gas. And, as Scott said, the kinetic energy component is larger than the momentum - both are conserved quantities, but because the kinetic component is larger, the direction of the particles emitted in the explosion is relatively spherical. They will be biased towards the direction of the impactor, but this contribution is swamped by the other term since it's scaled higher.

[@bmcwxyz]

The end product is hardly a snapshot if you refer back to 2:10.

[@dongurudebro4579]

You could also just say that each object has a given force holding it together if that force is overcome by a collision it "explodes". You can even try that with snowballs at home - the harder you squish the ball the harder you have to throw him to explode same goes for the angle.

[@affinecreations8114]

“The scalar mode has much more energy than the vector mode.” Talk about burying the lede.

[@OrionBlarg]

This was pretty interesting from a military perspective. I was an Forward Observer in the Army and one of the skills we were taught was crater analysis. Basically we would look at the craters made by things like artillery and mortars and determine information about it. Basically what direction the round came from and what kind of weapon system fired it. We could tell this usually by looking at the ejecta and comparing it to the shape of the crater itself and get a workable azimuth to the point of origin. Determing the weapon system usually came down to comparing shell fragments to determine how big the round was. This information was used to figure out generally where a hostile artillery or mortar position could be. An interesting quirk that creates a difference between a crater made by a mortar one by artillery is that the ejecta from an artillery piece will blow away from the direction the round came in. But with a mortar it tends to blow back towards the direction it came from almost as if its trajectory started to curve back in on itself. I think this has to do with the fact that mortars are fired at a high angle while artillery ends to be fired at a flatter trajectory (but they are able to fire at high angles). I'm guessing that things are different considering that artillery and mortar rounds come packed with their own chemical explosive energy to release on impact. But if you look at old aerial photos from WWI battlefields for example the craters are also almost always circular so I think the same rules may apply. I only had to use this skill in Afghanistan once when it turned out to be a recoilless rifle round harassing our outpost every now and then. This was a bit confusing because recoilles rifle rounds look just like mortar rounds but the ejecta blows away from the direction it was fired from. Just some random thoughts on craters.

[@bodkinofnurk8898]

Nice one... Thanks for that.

[@jakobfeitzinger9587]

The ejecta from the mortar goes back to where the projectile came from because of the area of low pressure that has been made by the incomming projectile (I think)

[@BasePuma4007]

Very interesting, thanks for posting this.

[@MrGrace]

The more you know 💫💫💫 Thank you for your service 🙏🏿

[@hightechredneck3362]

You're input matches nicely with a video I saw at Meteor Crater in Arizona. It was assumed at first the the meteor came in perpendicular due to the circular crater. But the area of the highest concentration of meteor fragments is the Northwest quadrant. How could there be an almost perpendicular approach angle but distribution of the fragments that almost looked like a horizontally fired shotgun? Enter one observant hunter. He noticed that if he missed his shot during the dry season, the bullet plowed a furrow. If he missed a shot when the ground was wet/muddy, it produced a circular crater. To the best of our knowledge, what is now Arizona was part of an ocean at one point. I don't think it's too much of a stretch to accept that the presence of liquid when Meteor Crater was formed is what gave the bowl shape and discrepancy of higher concentration of fragments in the NE quadrant. Concerning WWI heavy munitions craters, from the accounts I heard from those "Over there" was that it was almost always like wading through a bog. That could give further credibility to the hunter's theory concerning the presence of liquid at time of crater formation. Afghanistan-- yes, I would think that having to switch gears from forest to desert conditions would make reverse trajectory calculation a bit of a problem. I noticed that all my skills while stationed in the Mojave desert had to relearned and required rethinking when I was assigned to North Carolina. The interplay between humidity, air pressure and temperature became more pronounced than in the low humidity variation of the desert.

[@gordonrichardson2972]

The fact that most lunar craters are circular, led to the misunderstanding that they must be volcanic in origin. Only when the physics of hyper-velocity impacts became understood, did the volcanic theory fall out of favour.

[@gordonlawrence4749]

NoNoNo it's cos holes in cheese are circular.

[@Cythil]

Huh... I do not think people have seen that many volcanos in real life. They tend far from perfect circles and not look like creates. Of course there are a ton of different types of volcanos and a few of them do look like impact giant creates at first glance. But I would not say that is that common based on what I have seen.

[@gordonrichardson2972]

Its well documented: en.wikipedia.org/wiki/Lunar_craters "The competing theories were (a) volcanic eruptions blasting holes in the Moon, (b) meteoric impact" "Grove Karl Gilbert suggested in 1893 that the Moon's craters were formed by large asteroid impacts. Ralph Baldwin in 1949 wrote that the Moon's craters were mostly of impact origin. Around 1960, Gene Shoemaker revived the idea."

[@PHeMoX]

@gordon Richardson: The suggestion that the 'volcanic crater' theory ever had a large support is extremely false. Theories that were discarded extremely fast were the volcanic crater and also the glacial impact theory, both of which would have resulted in wildly different crater shapes.

[@gordonrichardson2972]

@PHeMoX Theories are only discarded when hard scientific evidence better supports the alternatives. Until then it does not matter how large or small the support is/was.

[@affegpus4195]

Tl;dr is the explosion that makes the crater not the weight draging on the surface

[@BlakeLinton]

Thanks! Great video, but I came away still not quite "getting" it intuitively. Your elegant little explanation does the trick!

[@daos3300]

Affe Gpus that doesn't make much sense. weight of what? in relation to what? the misunderstanding in question is about angles of impact, not weight of impactor.

[@neithere]

Or: it's displacement not by the direct impact, but by explosion caused by the impact. The explosion is omnidirectional and obliterates any trace of the original "touchdown".

[@StephenCameron]

Conservation of momentum and conservation of energy. Momentum is M*V, Energy is M*V*V. Energy dwarfs momentum. Only the momentum has direction.

[@figgeldorpe1053]

Tl;dw ^^^^

[@RoadsideCookie]

Why do meteors always land in craters?

[@timothyfair6058]

thats a good one hahahahaa!

[@scottmanley]

The funny thing about this joke is that on the moon you'd be hard pressed to find any bits of meteor in a crater on account of it being vapourised.

[@Eagles_Eye]

@@scottmanley well on the moon this joke would go too : "yow dog, i heard you like craters, so here is a crater within a crater within a crater within a crater - etc "

[@StYxXx]

Some "alternative science" conspiracy theorists take this joke more serious than you might expect....

[@dmitrilebedev8635]

As a soviet joke says, the officer lectures students: "Nuclear bomb always hits the ground zero." I don't think it's a coincidence.

[@thelonelyrogue3727]

Craters are circles to make it easier for the developers to model the Mun.

[@itsahumanperson6174]

Lmao.

[@CarlosAM1]

I imagine the people from squad selecting the circle shaped depth tool and going crazy by hitterclicking the surface.

[@thelonelyrogue3727]

@@CarlosAM1 that's exactly what I had in mind, lol.

[@lazyjackass77]

The Lonely Rogue - Looks like the cannabinoids are kicking in. Very funny.

[@JCO2002]

What's a Mun?

[@JoeBissell]

7:15 anything below 15 degrees is basically the universe just trying to skip stones

[@CharlieFoxtrot]

I'd honestly like to see what that would do to a planet with decent sized rocks

[@Calliopa_22]

Hey Joe, your profile pic is my desktop background xD!

[@madshorn5826]

@@CharlieFoxtrot Not this planets anytime soon though...

[@schizophrenicenthusiast]

The universe must have quite the sense of humour to be throwing stones at the sea of tranquillity.

[@bastetknee9554]

Anything below 10 deree from the normal with spin,might be a trick shot.💥o➖😯

[@visualwarp9707]

Makes perfect sense to me. I think the explanation could be even simpler - so at low angles the point of impact the object carves out an elongated hole, but the resulting explosion from the heat and pressure where the bulk of the energy is delivered just obliterates that and it blows up like a bomb i.e. with a spherical pressure wave and debris in all directions. So that small oval is instantly replaced by a much larger circle. You never see it. Only at extremely low angles does it dig a trench because in those cases it drags across the surface and dissipates the energy less rapidly - sort of hitting the brakes and spreading the energy over a much wider distance. But anything more than a glancing blow, and the object stops quickly, delivers most of its energy at a single point, and goes kaboom. The result is more about the explosion than the approach angle of the object that caused it.

[@NemoConsequentae]

It doesn't even dig a trench, really. It creates a series of explosions that leaves a trench. Sort of like the difference between the hole left by a stick if dynamite, vs the trench left by the equivalent amount of det cord.

[@visualwarp9707]

Mykl Langridge ahhh yeah I get it. Very interesting - thanks for that.

[@dongurudebro4579]

You can but even simpler just say that each object has a given force holding it together if that force is overcome by a collision it "explodes". You can even try that with snowballs at home - the harder you squish the ball the harder you have to throw him to explode same goes for the angle.

[@KuraIthys]

@@dongurudebro4579 OK, I don't usually do this, but you've made the same comment with the same mistake at least 3 times now. 'angel' is the biblical being usually depicted as a person with wings on it's back. An 'Angle' is the circular measurement of the separation of two intersecting lines. (OK, that's not a great explanation, but it's hard to explain an angle in a way that isn't a circular reference.) In other words, your comment is about 'angles', not Angels.

[@dongurudebro4579]

@@KuraIthys thanks - still just a typo and its like 5:41 in the morning and havent slept for like 42hours...^^ :)

[@Nuovoswiss]

Another point of interest here is that objects traveling at ~10 km/s have more kinetic energy than chemical bond energy holding them together. With that much energy, the fact that the projectile (or the impact surface) is solid doesn't really matter.

[@leocurious9919]

1:29 is the part you seem to have missed.

[@Nuovoswiss]

@@leocurious9919 Yea, he touched on it, but I thought it could use clarification/expansion. It's odd to think about it not mattering whether the impactor or surface is solid or liquid, since the energies are so high.

[@leocurious9919]

@@Nuovoswiss Well the impactor is solid. But it doesnt stay that way... pretty much.

[@gehovagyra1635]

So, does a pebble thrown into a pond create a round ripple or an elongated one?

[@gehovagyra1635]

It's also interesting to consider that while solids become as liquids at higher velocities, liquids become as solids at lower velocities.

[@exoplanets]

Great video! It was impressive to see an asteroid hiting the Moon during the last eclipse, it truly makes me appreciate our atmosphere

[@GunjerSpinners]

wait untill you see a person trying to breath on the moon, then you will truly appreciate our atmosphere

[@Paulo-py4mm]

I appreciate it's oxygen content more atm 😂

[@chicofromph33nix64]

I'm just waiting to see somebody on the moon

[@bipolatelly9806]

lol Impacts don't occur. Scott is full of it.

[@Mrbfgray]

@@bipolatelly9806 Are you a troll or just stupid?

[@EtzEchad]

Bottom line: with high velocity impacts, energy dominates rather than momentum. Rather than the analogy of throwing a rock into sand, think of it as throwing a hand-grenade into sand.

[@DoctorLodi]

David Messer that’s an especially good (but dangerous) model because there’s a delay between impact and explosion where you can see the minor trench before it gets obliterated by the explosion

[@matthewwynn3025]

Good analogy

[@fsmoura]

9:19 _"Total data: 266 TB"_ wow, almost like my documentaries folder

[@tempname8263]

I bet 265.99 TBs of that are just log files telling that memory is full.

[@gordonrichardson2972]

Maybe that's not disk storage, but RAM...

[@PHeMoX]

That's a lot of pron.

[@nilsp9426]

"documentaries" :D

[@Blubb5000]

PHeMoX I just wanted to say that.

[@velotegra7156]

I really liked your summary of the reason they are round: kinetic energy is a scalar whereas momentum is a vector, and at high velocities kinetic energy dominates, so direction (vector) of impact has little effect. Clear and insightful - Thanks.

[@SocksWithSandals]

It was only yesterday that I was throwing stones really hard into a muddy field wondering why the craters look different to those on the Moon. But you explained it - the stones were too slow to explode on contact. I should have been playing with grenades with short fuses!

[@Forklift_Fella]

Excellent video. You have answered a lot of questions I have had about impact craters.

[@rowannieuport3942]

In the late 70s when i was in high school i did a project firing ball bearings into a target of material that was very like sand, with a weak binding chemical so it wasn't like blasting a pattern. I had a high speed camera and used it to look at the ejecta pattern and crater. But visually, the resulting crater was essentially circular, even for oblique firings. The video mentions 1978, and yeah--that was when i was doing this project. I remember wishing i had a computer to simulate it, lol! There is nothing like living in a dark era, ahead of the progress to come. I remember that scientific papers back then did report that the craters were essentially circular, but there were no computer/fluid dynamic tools like today. It was not possible to report on subtleties. A wonderful video and channel!

[@connorlake3939]

For someone who barely scraped by in physics in high school, I must say - You make it so much less intimidating than all of the teachers I've seen teach it, and if you were a physics teacher, I can see your students doing very well. In my case for example, whilst watching your videos, I often find myself googling and trying to make sense of what is going on in the diagrams and graphs, and I can feel myself grasping what they mean and what you're saying. So I thank you sir :P

[@cokeforever]

As in that old anecdote: "you throw square bricks in the lake and see round waves" )

[@miklov]

@penn707 Rectangular cuboid please =P

[@luigivercotti6410]

@@miklov no, parallelepipeds

[@miklov]

​@@luigivercotti6410 Would be some low grade bricks then..

[@luigivercotti6410]

@@miklov ok, oblong rectangular parallelepipeds

[@miklov]

​@@luigivercotti6410 Are you saying that an oblong parallelogram would be a rectangle (square)?

[@coldspade1590]

Ejecta traveling through the low pressure zone created by the entry path is such a cool thing i didn’t expect to learn

[@johnnyhoran9369]

Finally someone who's actually good at explaining things EXPLAINS this, i've never gotten a straighter answer to this question than "Cuz kinetic energy makes big boom circle."

[@scottmanley]

The problem is it's really complicated to go from 'Big boom circle' to '3D hydrocode simulation'

[@johnnyhoran9369]

@@scottmanley I prefer 3D hydrocode simulations, just cause they look cool, not because i understand them.

[@maksphoto78]

But that's exactly what happens.

[@ParameterGrenze]

@@scottmanley The details might be complicated, but doesn't your explanation describe the basic physics correctly? The impact at high velocities turns a solid object into an expanding cloud of plasma. It also turns some of the ground material into expanding gas and plasma. This cloud has a velocity component in the direction of the impact, but it is small in comparison to the omnidirectional expansion created by turning kinetic energy into thermal energy. Basically you have a bomb which sets of at the moment of impact. Whether the bomb was flying in any direction does not matter much.

[@dongurudebro4579]

An easier explanation is that each object has a given force holding it together if that force is overcome by a collision it "explodes". You can even try that with snowballs at home - the harder you squish the ball the harder you have to throw him to explode same goes for the angel.

[@cragonaut]

Thanks for the recent trend in more technical content. It's great to see your channel doing some "deep dive" into the science of some of this stuff - all too often youtubers feel like they have to dumb down or gloss over the detail in order to appeal to their audience. And I always appreciate excerpts from actual papers rather than just the bed-time story approach.

[@NotMyActualName_]

The best experiment people can do at home (if they live somewhere cold) is to use a snowball. What's going on with a meteor impact is that the bonds within the material has to be able to survive the impact in order to make an elongated crater. If you hit rock against rock, above a certain energy level there's more force than the chemical to bonds in the rock can sustain and it just vaporizes. You can do this with a snowball against a brick wall too. Take a loosely packed snowball and throw it at a house. It will leave a circular mark every time. But pack it more tightly and from a shallower angle and it will eventually leave a streak.

[@thelovertunisia]

If craters were pits like those made by a falling stone, they would vary much more in size but since they are created by hypervelocity impacts, the impactor gets vaporized and it is like an explosion which creates a more or less bowl shaped crater.

[@_Egitor]

I tried to fly safe but then I impacted the moon at 2.16 degrees and now I'm embedded torso deep in regolith :(

[@amorembalming]

Rookie mistake.

[@NemoConsequentae]

Always remember: Lithobraking is not an approved landing method...

[@kindlin]

btw, [degree] is really easy, I use it all the time: alt-248; °. (hint: hold alt, press 2, 4, 8 on the numpad, release alt; it's like a numbered shortcut key for text.)

[@KuraIthys]

@@kindlin Those extended keypresses are hard to remember though. I mean it's fine if you only use one, but if you have 20-30 such extended characters it becomes hard to remember. Also I rarely have much luck getting the key sequence to work. Seems to have fiddly timing. °0°↑↑©° see? Not exactly reliable. XD And that's only the cases where it registered anything at all. Further, 'alt' also tends to open menus in most programs... It's sometimes useful, but as a scheme for entering extended characters in general it leaves a lot to be desired. Еª\°ÒÈ►│*Ð↑ nope. Can't manage much consistency with it. XD

[@kindlin]

@@KuraIthys Rofl, you don't need to _try_ and poke holes in the method. Everyone knows it's rarely used because of it's clunky-ness, but I use it often enough, specifically, for ° (248) and ± (241). I also sometimes use ≥ (242) and ≤ (243) which are easy to remember cuz they're right past 241 (as an engineer, I use ± and ° a _lot_ lol). Anyways, most people know about it, it's not hard, but most people don't bother to ever look them up. I've found these two to be very handy, myself. PS. This is super easy, stop trying to make it look hard. Look, I'll go from 230 to 250 for fun, hardly any slower than typing: µτΦΘΩΩδ∞φε∩≡±≥≤⌠⌡÷≈°∙·. OK, fine, that was a little annoying (I messed up 5-8 times), now lets try the two I do often, I won't use backspace: ±°±°±°±°±°±°±°±°±°±°±°±, easy enough for you?

[@TheZoltan-42]

Even shorter (and a bit superficial, pun intended): The dominant factor creating the visible change, the crater, is driven by the explosive effect of the impact which concentrates at the point of impact and retains little from the parallel motion. The ejecta produced by grazing the surface is indeed asymmetric, but for most impacts that yields only a fraction of the mass displacement and is also spread on a much bigger area. At very low angles where the explosion is much smaller and the grazing more prominent, you get the elliptical and trench type features. One more note: As most impacting objects arrive at small angles from the ecliptic, low angle impacts are more probable toward the poles where it's more difficult to spot using telescopes and the perspective rounds them back.

[@Spedley_2142]

So basically there is so much energy involved that the meteorite explodes on impact rather than transfer it's momentum to the moon like on a snooker table. Like having an explosive cue ball - it doesn't matter which direction you hit the red with if it just explodes.

[@philippeller2796]

I really liked the explanation about the energy (a scalar) scaling quadratically outgrowing the momentum (a vector quantity) that increases only linearly with speed; the scalar having no directionality the only thing it can do is essentially causing a circular shape

[@anarchyantz1564]

I love watching projectiles done using the NASA Ames vertical gun especially when they recreated the Chicxulub impact, that was nuts the sheer level of kinetic energy imparted. Not sure if they have recreated Earth's largest one though, the Vredefort crater, would be cool to see though.

[@ExaltedDuck]

Pretty sure Earth's largest crater is the space between it and the moon.

[@Saxie81]

This was such a good video. This video made me remember of an episode of the universe where they were shooting a BB into sand to show the trajectory of the debris, and even then they were circular. The question of why they were (mostly) circular never occurred to me.

[@timothymclean]

This reminds me of a bit in _The Moon is a Harsh Mistress,_ where some rocks chucked at Earth are initially mistaken for nuclear weapons. And they weren't even going at interplanetary speeds...

[@bernarrcoletta7419]

One of my favorite books too!

[@stcredzero]

"interplanetary speeds..." What does that even mean? Wouldn't a Hohman transfer orbit to Neptune have you doing about 5.4 km/s near apoapsis? I see. The escape velocity of the Moon is quite low, so a mass driver wouldn't be designed for much more than that. That's like 1/3rd of 5.4 km/s.

[@Emma_9999_]

@@SuperibyP Spoilers

[@SuperibyP]

@@Emma_9999_ ah shit yeah

[@LA-MJ]

The best part was murricans showing up on the x-marks-the-spot with picnic baskets and then media/gov complaining about unprovoked loss of life

[@mrnickbig1]

This answer is VERY easy. The energy of the impact, which is based on the square of the velocity FAR outweighs the momentum transfer, which is a linear relationship. Basically, a high delta V impact causes an explosion. Some oval craters DO exist, but the impactor has to be moving relatively slowly and hit at a shallow angle.

[@ghrey8282]

Thanks! That really made an impact.

[@cymrych79]

Zing!

[@Eryan724]

I dont care to follow all of these recent events of space exploration .... except for this channel. Its really interresting. Altho i dont even care too much about the topic at all. But you make it interresting! Youre a great presented, down to earth (haha pun), and great upload rate. Really respectable how you work! Thank you scott!

[@Jhonjackdiab]

Hey Scott it would be great if you could link the papers In the description for those that want to read further into the topic.

[@chhoc]

the animation starting at 5:37 was fantastic. I'd watch those in slow motion all day; the dynamics are amazing.

[@Kash-420]

11:00 "95% of craters unto a flat surface," are you saying the moon is flat? *gasp*

[@Geoffr524]

It's basically any surface, that is not a hillside, but is flat to the center of gravity.

[@Kash-420]

@@Geoffr524 I was just kidding because of the flat earthers that comment on Scott's videos sometimes.

[@garyoldham4449]

@@Kash-420 God did create the Earth flat under a crystal dome. But as soon as he did gravity warped space, it snapped into a spherical shape and the dome popped off. That's why we can see all them doo-hickeys flying around out there. No man, it's not CGI at all! That stuff is real!

[@micknight8158]

@@garyoldham4449 so.... Did GOD make a mistake creating heaven and earth? If God did, that means He is not perfect. Is that what your saying?

[@patreekotime4578]

@@micknight8158 the Bible is one long document of how God isn't perfect and keeps trying (and failing) to correct his mistakes and his imperfect creations.

[@markholm7050]

Thanks Scott, for retelling this story for a 21st Century audience. Sky and Telescope had an article covering the same ground (without video, since it was in the paper magazine) decades ago. Jeez, I’m getting old.

[@thekornwulf]

I'd bet the "astroid impacts" thing at Los Alamos is because of the old Rods from God idea. 'least, for the development of the software

[@gbsailing9436]

Don't forget that at sub-light speeds velocities will add. Most bodies in space are rotating, so forces on a body will also exhibit a resistant force in either a +ve or -ve direction to the incoming projectile/meteor, with many being velocities in alternate directions, not strictly +ve or -ve to the projectile, as projectiles can come from space in ANY direction and hit a spinning surface from any angle. Depending on speeds this effect or resultant addition or subtraction of energy may be significant. But taken with respect to overall acceleration of an object travelling throughout space, the additional momentum of the body being hit may be considered negligible. All these things need to be taken into account when considering the crater formation genesis. Not just the speed of the meteor.

[@Goldie644]

When things are travelling fast a lot of things become counter-intuitive - like the way supersonic airflow goes around a 90 degree corner :)

[@passthebutterrobot2600]

Especially things travelling close to the speed of light

[@williamrthompsonjr556]

@@passthebutterrobot2600 Like lightning?

[@AnunnakiAaron]

What happens in that scenario, I'm curious now. Does it have to do with creating a vacuum?

[@jeanpauldupuis]

At 6:09, bottom right - imagine a 'backdraft' vortex like this, but so energetic it extends all the way to the top of the atmosphere and persists for centuries...

[@xenon5]

I really like your channel, great work.

[@JoshtMoody]

Very cool explanation with the momentum versus kinetic energy scaling. Very good work as always, Scott.

[@OnionChoppingNinja]

why are most craters circular? Why so we humans just have to put a dome over it to make it a space habitat that's why!

[@SocksWithSandals]

I reckon the air pressure under a heavy flat glass, steel and concrete lid would keep it up for a large lunar settlement.

[@KaiHenningsen]

@@SocksWithSandals The real problem is the _next_ impactor.

[@Sableagle]

Somewhere in the Chinese footage, there was a crater in the dust in the crater in the dust in a crater.

[@Vandinium]

Irrelevant

[@wdwerker]

Even when Scott used terms and concepts beyond my knowledge the explanation still seemed valid, especially when he admitted that the entire topic is vastly more complicated. Thanks for bringing it down to a level we can grasp.

[@heyarno]

Thanks to Taofledermaus Mach 3 BB video, I wasn't surprised.

[@RWBHere]

Always wondered about that. Thanks for answering a very long-standing question, Scott.

[@UpcycleElectronics]

These simulations are very interesting to see. The solids and liquids get displaced a lot and that makes me wonder how this affects gases as well. How big does an object/impact need to be for it to substantially displace/disturb the atmosphere? Obviously something 80-100km in diameter is large enough to statically displace it's entire volume. So it is going to have a substantial effect at velocity. I wonder what effect asteroids have on the atmosphere in general as the size scales up. I imagine the atmosphere will behave much like a liquid. -Jake

[@whereswa11y]

WOW- thanks Scott this is perfect and timely. I have seen many asking why all craters are round.

[@danielmartens6369]

Hey Scott! You mentioned that the speed of sound is faster in Hydrogen. I know about it, but could you talk about the different speeds of sound in different gases and materials?

[@gordonlawrence4749]

Cody's Lab did that and some of it was quite funny.

[@lazyjackass77]

Daniel Martens - Check cody's lab for a video where he inhales most of the noble gasses and then talks for a while espousing his knowledge of the elements themselves.

[@stevebothe1416]

Nice call Daniel. I've always wondered what the speed of sound is in the Martian atmosphere and how this would effect the supersonic retro-propulsion that SpaceX use.

[@dongurudebro4579]

Its quiet easy the heavier a gas is the slower the sound is the light the faster - thats all! :) If you inhale Argon or Krypton for example you would sound like a totall bad ass! :)

[@suspicioustumbleweed4760]

Daniel Martens It’s the highest in a vacuum I think.

[@YC-ls4yx]

I am all for Thunderbolts Project to challenge the mainstream and I am a big fan of them, but since both models work and can produce similar results in the lab, I think people should keep an open mind. Until we detected a giant lightning on the surface of a planet that actually created a huge crater, I will go with the impact crater on this particular issue.

[@rushthezeppelin]

What about hexagonal craters and the abundance of bullseye and chain craters (specially the ones that don't have overlapping but joined edges)? I think the electromagnetic discharge theory better explains those.

[@ironclad452]

Precisely!

[@helpdeskjnp]

Oh this comment will be ignored completely since you pointed out something they are not willing to see.

[@helpdeskjnp]

You know, “them”, the “others”, haha, anybody but people who think 100% exactly like “us”. It was a generalized unfair statement that was meant to show frustration. It was a momentary lack of consciousness on my end and I retract any sarcasm or negativity I may have created, as it helps nothing by doing so. Thanks for your reply!

[@rushthezeppelin]

@Alexis Hazel DeSilva Lol I can't read right now and had to revise this first sentence twice already (I was critical to both yall in each previous iteration lol). I would lean back that way on the issue if someone can actual give an explanation using impactors only that isn't requiring an insane amount of circumstances to all line up just perfect (like a string of meteors all impacting at the exact same time to create the crater chains that do not have one crater overlapping the other but rather a straight rim between them). I know it shouldn't always be used but I think the electromagnetic discharge theory fits within Occam's razor better. Keep in mind the role of electromagnetic forces in the universe was once thought by the mainstream cosmology community to be essentially nil but more and more in the past 2-3 years I'm seeing them acknowledging they are playing more and more of a role, sometimes even on the galactic scale with regards to jets.

[@tomcan48]

Humm, we seem to have someone with awareness that things are not quite as they seem. The electric universe is taboo in the minds of science today. Instead, we need to accept the current dogma without question. Just look at Ultima Thule with deep so-called Impact Craters that should of destroyed them if an actual collision has occurred.

[@mankeez5892]

It's videos like this that make me glad I'm subscribed. Where else am I going to get information on lunar craters and their shape with that deep Scott narrator voice?

[@maksphoto78]

Long story short, most impact craters are circular because the explosion created by an impact is incredibly powerful. Think of a nuclear bomb heading to the surface at an angle. The nuclear explosion will be so powerful, the bomb's trajectory will not matter; the explosion will create a circular crater.

[@tempname8263]

Yep. Explosion forces propagate in spherical manner ejecting mass outwards symmetrically while at the same time overwriting the shift of upper layers caused by shallow angle of attack.

[@moosemaimer]

at sufficient velocities, all projectiles are high explosive.

[@forrestunderwood3174]

Actually, it appears any impact angle over 3° seems to leave a circular crater, albeit with an unconnected tail.

[@TheOnlyTominator]

"Lies to children"... I'm going to start using that.

[@blizzard4025]

this guy is relly experienced in what his talking he makes it sooooo simple to understand dude u could have become a realy good science teacher

[@ksp-crafter5907]

@Scott Manley it's just the simplest way to do the maths for the simulation we all live in! ;-D

[@lazyjackass77]

This comment did not receive the proper amount of attention. Here is another like.

[@dannyoman7219]

Rebound from the densest part underneath would also hide sideway projection , Awesome video thanks

[@flyingskyward2153]

Spherical crater in a frictionless vacuum

[@woodywiest]

"Regardless of what your intuition says..." Carry that one with you. I'm happy you exist Scott.

[@TraitorVek]

Most Craters are actually Hexagonal.

[@lazyjackass77]

Are they impact craters, though? There closely clustered and fractally interrelated hexagonal cratering everywhere we look. I'm not making a claim one way or the other, but someone has the proper and correct answer which also means someone is feeding me a load of crap, which also implies mass deception. Is it possible, or am I off my rocker and lost my marbles?

[@scottmanley]

Here's some light reading on polygonal craters www.researchgate.net/publication/260034157_The_Structural_Control_of_Polygonal_Impact_Craters

[@billroberts9182]

Wow, you are one smart guy-or you have friends who are really smart! Thanks for the explanation- My Dad worked for Boeing studying crater ejecta in the early 1960s (as part of the lunar project) so your article caught my eye. Thx!

[@smile768]

The moon was made in Area 51 by Stanley Kubrick. He only had circular stencils back then.

[@passthebutterrobot2600]

And a job lot of "army surplus" grey paint

[@rdfox76]

@@passthebutterrobot2600 Navy surplus, actually. They had a hell of a lot of extra battleship grey left over after they retired the battleships.

[@silkwesir1444]

rdfox76 " It is so called because the color is the shade of gray from the specular micaceous hematite paint used for rustproofing iron and steel battleships." (wikipedia) Oh, that's the reason! I had figured that color was a kind of "best compromise" for camouflage in various situations (day vs night, sunny vs cloudy, etc.)... even though made obsolete by today's technology, it stuck as a tradition, i thought

[@williamrthompsonjr556]

@@silkwesir1444 You mean "today's technology" as in red lead paint as primer for steel, and zinc paint for primer for aluminum? Grey paint is the final coat, and together they slow down corrosion, but never entirely prevent it. I was in the navy.

[@rdfox76]

@@silkwesir1444 Actualy, what the US Navy uses now isn't the same color. Ever since 1946, they've standardized on overall Haze Grey for vertical surfaces and Deck Grey for horizontal ones, because that was found to be the most generically effective visual camouflage. There were other schemes used in WW2, some of which were better in certain areas (and as such, ships were painted to match the area they were operating in), but with the assumption of being under constant radar surveillance, they thought it'd be easier to standardize on a single "good enough" paint job.

[@castletown999]

5:59 Ejecta will not travel back up the arrival path in space because the "low pressure" area will not exist in the vacuum of space.

[@jamescollier3]

Lol. Good point!!

[@andersjjensen]

I saw the "Electrical Universe" nuts on the moon impact video make wild claims about why the craters were round... where are you guys now? Come out and play.. It'll be fun! I promise! :P

[@williamrthompsonjr556]

If you start out by calling us "nuts", and that we make "wild claims", you demonstrate that you have no objectivity, and a closed mind. There is no one theory that explains why craters are round, and, if you are using the scientific method, you would know that no scientific theory is set in stone, that all of them are subject to falsification by new evidence found through new observations. The apparent impact seen during the recent eclipse, is possible new evidence supporting one theory or another, if observations can determine exactly where the light was seen, and if it left a new crater that can be photographed.

[@grahamhurlstone-jones5664]

Time to find out how it all works......its fun I promise....I wonder if you have the effort to study ? I have and it works....Im an electrical and did not see this coming.......Its the real thing but I am sure you will be good in your Einstein theories and large explosions everywhere......its wrong and we are busy proving it,.....its fun seeing the universe how it really should be seen......especially for the next generation who will not be lied to and will understand how it works.......come and learn....

[@cryptophasia8511]

craters clearly created by electric discharges, makes sense, 90 degree to surface, sculpted crater rims, circular, even we see meteors explode over the surface of the planet in massive electric discharge more than we see physical impact. e g Tunguska event.

[@cryptophasia8511]

@@googleeatsdicks more coming

[@daos3300]

Anders Juel Jensen that's too easy. where's the sport?

[@bryancrews7748]

I feel smarter every time I watch you. Thanks and I’m flyin safe!

[@LaurinV]

Who disliked the video :(

[@brucerandell3771]

The guy that didn't understand Scott's kid-level explanation.

[@lightyzhere]

Probably the guy who thinks the moon is a hologram.

[@passthebutterrobot2600]

Georges Méliès

[@sphericalsphere]

This was fascinating, I genuinely never even thought about it.

[@diveflyfish]

Scott, perhaps your explanatory frame of reference is limited, despite your "hideously Complex offered math explanation without the math of the actual event. The impact will not emit light just because of kinetics. In that your assumption of speed and kinetics is a assumption, without accounting for triboelectric effect or simple electric phenonema as compared kinetics and heat. Here is a question, what is the temp of a plasma lightening bolt in enough of itself? The heat is an impedance phenomena. I suggest that you seek out electric discharge phenomenology as an infinitely more plausible explanation. See Thunderbolts project and Electric Universe Theory. Again, do you agree there is a charge delta between the earth and Moon? If not why? Is there not a electric delta within our atmosphere? What would delimit the electric charge to be only on one planet? Would all planets have the same charge?

[@cryptophasia8511]

Nice

[@GregEwing]

You always have great sources and it is always easy to dig deeper. Also you don't ramble or anything. So... how long does it take you to produce a video like this?

[@frankmy18]

I'm so early that it's still 8k O_o

[@lostcoast707]

When I clicked it said zero views and no thumbs up... That's never happened to me on a big challenge. Great video as always thought.

[@PuReEnStyLez]

just watched an interview where NDGT talked and explained this. yours is good too 🙏

[@neilolif]

Excellent presentation. Nicely gathered studies!!!

[@spyersecol0013]

I learned this visiting meteor crater in northern Arizona. They have a really nice video explaining this.

[@bobbilaval6171]

Years ago when the Meteor crater was being studied in Arizona they experimented by firing bullets into soft mud and observed round impacts fired from almost any angle.

[@DoctoreDoom]

I use to think about this when I was younger as I had to mix concrete up. Very interesting stuff, thanks for making this video!

[@jhyland87]

The part about the ejecta going back up the trail path due to low pressure zone is really neat

[@smc4229]

Answering questions I didn't even know I had. Thanks Scott!

[@andrewsteinhaus8267]

Loved all the animations! Great question too! I never really thought about it. It really clicked for me when you said the energy didn’t have a direction, only the momentum of the object was. Thanks

[@rage42]

Very interesting and so many cool animations !

[@nathanaelvetters2684]

Hypervelocity impacts are so weird and unintuitive. It's nice to see these videos and simulations.

[@spelunkerd]

This video answers a question I have wondered about for decades. I had always assumed craters are round because the asteroid explodes on impact, releasing not just kinetic energy but also chemical energy. Evidently not!

[@TTaylor]

Earlier today while clicking on KZbin recommended videos, I watched a video where samali pirates were trying to run away from a US battle ship. A helicopter was given permission to fire a warning shot across the bow and when he did the bullet splashes went straight up from the impacts in the ocean. It didn’t seem counter intuitive when I watched it but I immediately thought of it when starting this video.

[@cyrylo23]

In 7:00 Ellipticity (ε) and eccentricity (e) are not the same thing. Ellipticity (e) is semi-major axis divided by semi-minor axis Eccentricity (ε) is distance from center to the foci divided by semi-major axis. ε = sqrt(1/(1 - e^2) So when impact angle is 10°, ε = 1.3 and e = 0.63.

[@scottmanley]

You are of course correct.

[@DieDreiMenschen]

What a nice, well researched, informative video! You really dig in deep and keep your video quality at an impressive level! Greetings from Germany!

[@genericscottishchannel1603]

i was wondering where I could get my hands on this software, then I saw the 266 TB

[@rfbyrnes]

Great job, well done. Thank you for butting this togeher.

[@tomjones1258]

Video Controls: pause: 'k', advance and reverse 1 frame: '.' and ',' advance and reverse 5 sec: left and right arrow key, advance and reverse 10 sec: 'j' and 'L' keys

[@jdrew500]

The most interesting thing, to me, was the ejection of material back up the low pressure area following the path of the incoming projectile. Because most craters are round(ish) this would help with figuring out the incoming direction thousands of years later.

[@TheDannielboy]

Interesting subject! I live in Canada, and we often have light snow or sometimes slushy ice on the ground or in the pool, it's than very easy to test this phenomenon yourself. I myself observed it by mistake in the middle of a snowball fight and thought it was very interesting that i never noticed it before..

[@MatthewSuffidy]

It looks like the problem is a small region of high heat's effect on the region around it, except for the case of low angle impacts, where some of the impact is not necessarily happening at exactly the same point, but drags on.

[@christosvoskresye]

The short answer is that although momentum is proportional to speed, kinetic energy is proportional to speed squared. For a really fast impactor, energy considerations (which tend to make it like a stationary bomb going off) are more important than momentum considerations (that would make it lopsided).

[@erigoasparago]

Love it! I'm gonna use this for my class! Thank you Scott :-)

[@deusexaethera]

TL;DR: Most craters are round because the impactor _and_ the target both explode on impact, and they explode in a roughly-spherical pattern at all but the most shallow impact angles. The kinetic energy of a hypersonic impactor is orders of magnitude larger than its momentum, and kinetic energy doesn't convey a directional force like momentum does. So when that kinetic energy is transferred to the expanding cloud of vaporized rock, the direction of the impactor's momentum has only a minuscule effect on the trajectories of the ejecta particles.

[@zippy3711]

The easy answer is, when a hyper speed object hits, it is more like an explosion in that spot, then an object coming to that spot. But I like the way Scott explains it also.

[@daveh3997]

When I was a kid, I used to go shooting .22s with my Dad in the desert. Sometimes we'd shoot down towards dry creek beds at the bottom of gulches. I noticed the bullets always made round holes. Never realized we were making impact craters like on the moon.

[@milliondollaroptions]

Nice job, I can honestly say that I am smarter after watching your video. For that, a hearty thumbs-up!

[@Ai-he1dp]

Interesting, I have wondered why and this presentation makes it more clear to me, thank you!