# Everyone knows that the moon has craters, right? But when was the last one recorded? **URL:** \ **Category:** Factual Questions\ **Created:** [April 11, 2021, 5:42pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807 "2021-04-11T17:42:29Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 12, 2021, 8:49pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/41 "2021-04-12T20:49:26Z")
FWIW, during the time the majority of meaningful impacts were happening in the very early solar system, the Earth and moon would have sheltered each other a _little_ bit better because of the much smaller distance between them. > **[What Did The Moon Look Like From Earth 4 Billion Years Ago?](https://www.forbes.com/sites/quora/2018/07/11/what-did-the-moon-look-like-from-earth-4-billion-years-ago/?sh=17f6100d1151)** > > If we had a time machine, what would the moon look like from Earth 4 billion years ago? This question was originally answered on Quora by Corey Powell. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [April 13, 2021, 9:37am UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/42 "2021-04-13T09:37:45Z")
> [@Darren\_Garrison](#): > > And it keeps going down–individual grains of “sand” have microscopic impact craters. No need for the quotes - when it comes to rocks/minerals, if it’s [sand-sized](https://en.wikipedia.org/wiki/Grain_size) (1/16 to 2 mm), it _is_ sand, regardless of where in the Universe it is or what its precise composition. ---
**Author:** ![scudsucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scudsucker/32/14101_2.png) [@scudsucker](https://boards.straightdope.com/u/scudsucker)\ **Post date:** [April 13, 2021, 12:32pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/43 "2021-04-13T12:32:46Z")
A bit of a tangential question: the majority of known craters on earth and the moon are roughly circular. This means (to me, at least) that the meteor was on a trajectory roughly perpendicular to the surface where impact occurred. Is this the case? And if not… then: If it came in at a more acute angle, the “crater” would surely have much more debris on one side, and the shape should be more oval. And if it came in at a very acute angle to the eg, 10˚ to the tangent, (ie, 80˚ to the perpendicular) would it “bounce” and breakup without much trace? Chelyabinsk appeared to be in this category but broke apart before landing. A bigger body might actually hit land. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [April 13, 2021, 1:34pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/44 "2021-04-13T13:34:04Z")
> [@scudsucker](#): > > A bit of a tangential question: the majority of known craters on earth and the moon are roughly circular. This means (to me, at least) that the meteor was on a trajectory roughly perpendicular to the surface where impact occurred. Is this the case? And if not… then: Not really, an impact at nearly any angle is going to leave a circular crater. > **[Why are impact craters always circular?](https://www.sciencefocus.com/space/why-are-impact-craters-always-circular)** > > If you throw a stone into mud at an angle you normally end up with a ‘crater’ that’s elliptical or elongated, but is it the same when it comes to impact craters? > [@](#): > > At the moment of impact this enormous kinetic energy is almost entirely converted into heat, which then vaporises the meteoroid instantly. It’s this ‘explosion’ and not the meteoroid itself that creates the impact crater. Since material is ejected equally in all directions, regardless of the direction of travel of the meteoroid, the resulting crater is circular. There can be exceptions to this but only if the impact occurs at an extremely shallow angle. There are of course more in depth treatments of this topic if you are interested. > [@scudsucker](#): > > And if it came in at a very acute angle to the eg, 10˚ to the tangent, (ie, 80˚ to the perpendicular) would it “bounce” and breakup without much trace? No. However, at _that_ shallow of an angle, you may actually see a distortion in the crater along the trajectory. > [@Keeve](#): > > To me, the above explains why the far side of the moon is rather uniform and is totally covered with random craters, whereas the near side - which has been protected by the earth to some degree - still retains the gigantic “seas” of so long ago. There have simply been fewer meteors hitting the near side to ruin the scenery. > > Surely someone smarter than me has either confirmed or debunked this idea. Anyone know? I’ve seen a couple explanations for the asymmetry. The more recent that I saw involved a double collision theory, that after the moon had mostly formed it got hit again. I’m a bit skeptical on that one. The one that I put more credence in is that the moon was affected by the heat of the Earth. The moon would have spun down and become tidally locked fairly quickly, while the Earth’s surface was still mostly molten and blazing at a few thousand degrees. It was also much closer to the Earth than it is today. So, the side facing the Earth had a big oven in the sky, altering its composition and evolution. Jury’s still out though, and we learn something (or a bunch of somethings) about the moon everytime we send a new probe. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [April 13, 2021, 1:43pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/45 "2021-04-13T13:43:39Z")
Once the moon was tidally locked, couldn’t the Earth’s gravity have pulled the liquid magma towards the side facing Earth? Just like the Sun and the Moon pull oceans on Earth towards them? ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [April 13, 2021, 1:46pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/46 "2021-04-13T13:46:28Z")
> [@k9bfriender](#): > > Not really, an impact at nearly any angle is going to leave a circular crater. Scott Manley does _excellent_ videos on rocketry and space exploration topics, and he’s got a great one I just happened to watch the other day about exactly this subject. 11 minutes long, but with detailed explanations and experiment footage to illustrate why only _very_ shallow-angle impacts leave noticeably oblong craters: [![](https://img.youtube.com/vi/BCGWGJOUjHY/hqdefault.jpg "Why Are Most Impact Craters Perfectly Circular? (Rather than Ovals)") ](https://www.youtube.com/watch?v=BCGWGJOUjHY) ---
**Author:** ![scudsucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scudsucker/32/14101_2.png) [@scudsucker](https://boards.straightdope.com/u/scudsucker)\ **Post date:** [April 13, 2021, 1:55pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/47 "2021-04-13T13:55:01Z")
Thank you, great explanation. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [April 13, 2021, 1:58pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/48 "2021-04-13T13:58:17Z")
You note that the tidal bulge on Earth is both on the side facing the moon, and also the side away from it? Tidal action is less about pulling, and more about squeezing. > [@Machine\_Elf](#): > > Scott Manley does _excellent_ videos on rocketry and space exploration topics, and he’s got a great one I just happened to watch the other day about exactly this subject. Love his channel, would probably have linked to that video if I was at home, rather than work. It’d be much easier to find on my home computer. But yeah he’s certainly become one of the better science popularizers out there. I originally just started watching for Kerbal Space program. Was looking for tips on how to get my rockets to do what I wanted them to do, and found that I preferred watching him play than playing myself. Scott Manley: Come for Kerbal, Stay for the Universe. 🙂 ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [April 13, 2021, 1:59pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/49 "2021-04-13T13:59:21Z")
> [@k9bfriender](#): > > You note that the tidal bulge on Earth is both on the side facing the moon, and also the side away from it? No, could you explain please? ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [April 13, 2021, 2:11pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/50 "2021-04-13T14:11:32Z")
I could let an ex-Doper explain… [![](https://img.youtube.com/vi/KlWpFLfLFBI/maxresdefault.jpg "Tides: Crash Course Astronomy #8") ](https://www.youtube.com/watch?v=KlWpFLfLFBI) ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 13, 2021, 3:05pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/51 "2021-04-13T15:05:00Z")
> [@MrDibble](#): > > No need for the quotes - when it comes to rocks/minerals, if it’s [sand-sized](https://en.wikipedia.org/wiki/Grain_size) (1/16 to 2 mm), it _is_ sand, regardless of where in the Universe it is or what its precise composition. Since you’re an expert in the field I’m not about to quibble with your terminology. And what follows is not meant as any sort of criticism, just as a vaguely humorous observation … Obviously any terminology in English is just our semi-arbitrary name for {whatever}, and we need an agreed term to communicate successfully with one another. So far, so ordinary. But the shear humanity-centric hubris of flatly declaring it to be “sand” everywhere in the Universe struck me funny. I wonder if the jillions of folks on sextillions of other planets in billions of other galaxies agree with that? It’s simultaneously a humdrum and an outrageous statement. I chuckled. Maybe someone else will too. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 13, 2021, 3:15pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/52 "2021-04-13T15:15:16Z")
> [@scudsucker](#): > > And if it came in at a very acute angle to the eg, 10˚ to the tangent, (ie, 80˚ to the perpendicular) would it “bounce” and breakup without much trace? Look at section 3 here for an example of a possible "bounce: [http://craterexplorer.ca/crater-structure/](http://craterexplorer.ca/crater-structure/) ---
**Author:** ![gnoitall](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@gnoitall](https://boards.straightdope.com/u/gnoitall)\ **Post date:** [April 13, 2021, 3:25pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/53 "2021-04-13T15:25:26Z")
Forgive my ignorance, but which ex-Doper is that? ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 13, 2021, 3:26pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/54 "2021-04-13T15:26:09Z")
> [@MrDibble](#): > > No need for the quotes - when it comes to rocks/minerals, if it’s [sand-sized](https://en.wikipedia.org/wiki/Grain_size) (1/16 to 2 mm), it _is_ sand, regardless of where in the Universe it is or what its precise composition. An individual grain of that size can be called sand, but I don’t want to imply that a handful scooped up from the lunar surface would be concidered to be sand overall like sand on a beach. Lunar regolith as a whole is largely unsorted by size in a way most Earth sediments aren’t. Here a chunk of regolith impact-fused into a solid breccia: [https://thumbs.worthpoint.com/zoom/images1/1/1217/08/nwa-11266-lunar-feldspathic-regolith\_1\_7800f317a432771ea3b3d4549e353167.jpg](https://thumbs.worthpoint.com/zoom/images1/1/1217/08/nwa-11266-lunar-feldspathic-regolith_1_7800f317a432771ea3b3d4549e353167.jpg) ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [April 13, 2021, 3:32pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/55 "2021-04-13T15:32:41Z")
Sure, fair enough, but then just _use_ regolith, not “sand” - anyone reading you who is scared of a little technical jargon will just have to deal, IMO. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [April 13, 2021, 3:34pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/56 "2021-04-13T15:34:28Z")
BadAstronomer ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [April 13, 2021, 3:44pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/57 "2021-04-13T15:44:27Z")
> [@LSLGuy](#): > > As **Darren** says, Earth’s gravity bends the path of income asteroids a smidgen. Can you tell me where I can sign up for one of these income asteroids? I can always use some spare cash. \* \*You once shamed me for writing _de juro_ when I meant _de jure_. I now have my revenge. 😃 ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 13, 2021, 3:50pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/58 "2021-04-13T15:50:03Z")
> [@Darren\_Garrison](#): > > Here a chunk of regolith impact-fused into a solid breccia: It appears that image won’t hotlink, at least not without a membership. I get a 403 Forbidden error. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 13, 2021, 3:53pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/59 "2021-04-13T15:53:12Z")
> [@wolfpup](#): > > Can you tell me where I can sign up for one of these income asteroids? I can always use some spare cash. \* > > \*You once shamed me for writing _de juro_ when I meant _de jure_ . I now have my revenge. Touché Good Sir! The bad part is when the income asteroid impacts your existing nest egg at speed the whole thing is turned into a rapidly expanding cloud of used-to-be gold plasma. Capturing and re-condensing the plasma is a tall order. Said another way: > There is no free crunch! ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 13, 2021, 4:08pm UTC](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807/60 "2021-04-13T16:08:06Z")
> [@LSLGuy](#): > > It appears that image won’t hotlink, at least not without a membership. I get a 403 Forbidden error. The lunar meteorite NWA 11266: [https://imgur.com/a/yZSMoGb](https://imgur.com/a/yZSMoGb) [Previous page](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807.md?page=2) [Next page](https://boards.straightdope.com/t/everyone-knows-that-the-moon-has-craters-right-but-when-was-the-last-one-recorded/939807.md?page=4)