<p>There are elongated craters from grazing impacts, and these can sometimes get rather odd shapes like <a href="https://en.wikipedia.org/wiki/Schiller_(crater)" rel="nofollow noreferrer">Schiller</a> on the Moon and <a href="https://en.wikipedia.org/wiki/Orcus_Patera" rel="nofollow noreferrer">Orcus Patera</a> on Mars (the later is a bit contested, it might have formed from something other than an impact).</p>

<p>Double impact craters is another possibility. <a href="https://hirise.lpl.arizona.edu/ESP_020894_1395" rel="nofollow noreferrer">Some craters occur simultaneously</a> (<a href="http://www.nbcnews.com/id/41836713/ns/technology_and_science-space/t/mars-meteorite-craters-make-mine-double/" rel="nofollow noreferrer">more direct picture</a>). Splitting impactors is likely the one way of getting truly complex topologies. Most of the time they tend to follow each other, producing <a href="https://en.wikipedia.org/wiki/Crater_chain" rel="nofollow noreferrer">crater chains</a>. </p>

<p>If terrain shifts craters may be deformed, and depending on details in the rock they may also get odd shapes. <a href="https://en.wikipedia.org/wiki/Meteor_Crater" rel="nofollow noreferrer">Meteor Crater</a> in Arizona is somewhat squarish.</p>

<p>Craters cannot generate that complex patterns since they are just explosions out from a center and impactors are usually single objects or random clouds. In principle one could arrange asteroids along a trajectory to spell out letters upon impact, but it is an exceedingly unlikely configuration so most impacts will only manage 'O'.</p>

CC BY-SA 3.0
2018-03-06T06:29:03.483Z
A great comprehensive reply which helps broaden the discussion. A thought experiment - take an impact like shoemaker-levy, increase the amount of fragments reduce their separation distance ...what would this produce?
Dan
CC BY-SA 3.0
2018-03-06T09:53:40.233Z
That would make a crater chain. Hmm, I should probably add that to the answer.
Anders Sandberg
CC BY-SA 3.0
2018-03-08T07:44:03.803Z
Actually, you did mention crater chains in your original answer. As you might guess I'm trying to develop this thought experiment in a particular direction...to take it further - imagine a variety of sizes for a disintegrated bolide with the gaps in between consisting of much smaller fragments like gravel, possibly under a power law distribution. what does this impact look like?
Dan
CC BY-SA 3.0
2018-03-05T23:20:03.010Z
2018-03-06T09:55:06.270Z
2018-03-06T09:55:06.270Z
Anders Sandberg
<p>Impact craters are not always circular. They vary based on the angle of incidence.</p>
<p>One example is the <a href="https://en.wikipedia.org/wiki/Wetumpka_crater" rel="nofollow noreferrer">Wetumpka crater</a>. There is also research on <a href="https://www.sciencedirect.com/science/article/pii/S0032063314001093" rel="nofollow noreferrer">Asymmetric craters on Vesta: Impact on sloping surfaces</a> which states e.g.</p>
<blockquote>
<p>The global occurrence of these crater classes compared with a slope map clearly shows that these asymmetric crater types exclusively form on slopes.</p>
</blockquote>

CC BY-SA 3.0
2018-03-05T19:37:19.923Z
This answer would benefit a lot if you write a few lines explaining what's in that report.  Specifically, that noncircular formations are almost exclusively limited to steep slope ground formations.   Niven, in Lucifer's Hammer, refers to existing (at that time) studies which show that craters are essentially circular regardless of impact angle for "normal" circumstances.    //  My reading of your link is that noncircularity depends a lot more on the slope steepness than the relative angle of impact.
Carl Witthoft
CC BY-SA 4.0
2021-02-23T22:17:03.277Z
I tried making the post more accessible by including a quote and adding a link. Hope that's fine for all.
B--rian
CC BY-SA 4.0
2018-03-05T19:01:46.877Z
2021-02-23T22:16:01.290Z
2021-02-23T22:16:01.290Z
bandybabboon
<p>I'm aware for over 100 years the reason has been known how impact craters are almost always circular, but my question really is has there been any recent insights in the area? What other topologies are physically possible? </p>

CC BY-SA 3.0
2018-03-05T16:10:09.050Z
Well... do you include grazing incidence gouges? These are easy to create with an aerodynamic structure like an airplane, but statistically unlikely for exo-terran objects.
Carl Witthoft
CC BY-SA 3.0
2018-03-05T19:12:43.763Z
Was the formation of the  Río Cuarto "craters" ever definitely decided?
James K
<planet><formation><surface>
Are all impact craters circular?
Dan
# Are all impact craters circular?

(Asked by: username_0 on 2018-03-05)

I'm aware for over 100 years the reason has been known how impact craters are almost always circular, but my question really is has there been any recent insights in the area? What other topologies are physically possible?

**Tags:** planet, formation, surface
> **Comments:**
> **username_1**: Well... do you include grazing incidence gouges? These are easy to create with an aerodynamic structure like an airplane, but statistically unlikely for exo-terran objects.  
> **username_2**: Was the formation of the  Río Cuarto "craters" ever definitely decided?  

---

## 2 answers

### Answer by username_3 on 2018-03-05. Score: 5

There are elongated craters from grazing impacts, and these can sometimes get rather odd shapes like [Schiller](https://en.wikipedia.org/wiki/Schiller_(crater)) on the Moon and [Orcus Patera](https://en.wikipedia.org/wiki/Orcus_Patera) on Mars (the later is a bit contested, it might have formed from something other than an impact).

Double impact craters is another possibility. [Some craters occur simultaneously](https://hirise.lpl.arizona.edu/ESP_020894_1395) ([more direct picture](http://www.nbcnews.com/id/41836713/ns/technology_and_science-space/t/mars-meteorite-craters-make-mine-double/)). Splitting impactors is likely the one way of getting truly complex topologies. Most of the time they tend to follow each other, producing [crater chains](https://en.wikipedia.org/wiki/Crater_chain).

If terrain shifts craters may be deformed, and depending on details in the rock they may also get odd shapes. [Meteor Crater](https://en.wikipedia.org/wiki/Meteor_Crater) in Arizona is somewhat squarish.

Craters cannot generate that complex patterns since they are just explosions out from a center and impactors are usually single objects or random clouds. In principle one could arrange asteroids along a trajectory to spell out letters upon impact, but it is an exceedingly unlikely configuration so most impacts will only manage 'O'.

> **Comments:**
> **username_0**: A great comprehensive reply which helps broaden the discussion. A thought experiment - take an impact like shoemaker-levy, increase the amount of fragments reduce their separation distance ...what would this produce?  
> **username_3**: That would make a crater chain. Hmm, I should probably add that to the answer.  
> **username_0**: Actually, you did mention crater chains in your original answer. As you might guess I'm trying to develop this thought experiment in a particular direction...to take it further - imagine a variety of sizes for a disintegrated bolide with the gaps in between consisting of much smaller fragments like gravel, possibly under a power law distribution. what does this impact look like?  

---

### Answer by username_4 on 2018-03-05. Score: 1

Impact craters are not always circular. They vary based on the angle of incidence.

One example is the [Wetumpka crater](https://en.wikipedia.org/wiki/Wetumpka_crater). There is also research on [Asymmetric craters on Vesta: Impact on sloping surfaces](https://www.sciencedirect.com/science/article/pii/S0032063314001093) which states e.g.

> The global occurrence of these crater classes compared with a slope map clearly shows that these asymmetric crater types exclusively form on slopes.

> **Comments:**
> **username_1**: This answer would benefit a lot if you write a few lines explaining what's in that report.  Specifically, that noncircular formations are almost exclusively limited to steep slope ground formations.   Niven, in Lucifer's Hammer, refers to existing (at that time) studies which show that craters are essentially circular regardless of impact angle for "normal" circumstances.    //  My reading of your link is that noncircularity depends a lot more on the slope steepness than the relative angle of impact.  
> **username_5**: I tried making the post more accessible by including a quote and adding a link. Hope that's fine for all.  

---

