Hexagonal Craters: Airless Worlds & Moons Explored

[GregM]

TL;DR Summary

Hexagonal craters. Why?

On airless rocky worlds, why are so many craters hexagons? There are even some pentagons. I see them on the Moon, Mercury, Ceres, Mars, Mimas... It's quiker to note the airless worlds that don't have have hexagon craters.
This one is Ceres.

We can use this thread as an image repository for hexagonal craters.

 

[Motore]

Summary: Hexagonal craters. Why?

On airless rocky worlds, why are so many craters hexagons?

How many? On the picture above I also see a semicircular with two flat sides crater, an octa or decagonal crater, ...

Check this for brief explanation:
https://www.jpl.nasa.gov/images/pia23448-hexagon-crater

And more general this:
https://en.wikipedia.org/wiki/Impact_crater#Crater_formation

 

[GregM]

>How many?
You've mistaken me for a member of the ESA 10 year long solar system crater survey team. Very flattering, in return I'll mistake you for a fellow member: How many round craters are there in the solar system?>Check this for brief explanation:
a rather vague arm wave at possile explanations.

i've fished out the explanation for you:
"The regional surface/subsurface fracture system deflected the impact generated pressure waves along the tectonic network, causing the linear sides we see in the image."

So is that the consensus reason for hexagonal craters in the solar system?
the impact crater link doesn't mention hexagon or any polygon shaped craters so its not useful.

 

[GregM]

Mimas with its large hexagon crater 'Herschel'

 

[Motore]

Well I don't see the green marked one as hexagonal but a semicircle with two flat side. The brown bottom left one is a polygon of at least ten sides. So even the two of us can't agree on the shape of some craters on the picture in post #3.
On the picture on post #4 I also don't see the big crater as hexagonal, it is somewhat a complex shape. It's also a complex crater:
https://en.wikipedia.org/wiki/Complex_crater

You've mistaken me for a member of the ESA 10 year long solar system crater survey team. Very flattering, in return I'll mistake u for a fellow member: How many round craters are there in the solar system?

According to various sources (like this one) most of the craters are circular, so I guess the hexagonal ones are a minority.

i've fished out the explanation for you:
"The regional surface/subsurface fracture system deflected the impact generated pressure waves along the tectonic network, causing the linear sides we see in the image."

Yes that is the link I found for you and I don't see any problem with this explanation of why a polygonial crater can form. What other search have you done?

 

[GregM]

>I don't see the green marked one as hexagonal but a semicircle with two flat side.
Perhaps we've got a case of 'I don't think the heart is on the left side of the body'. It took centuries for experts to overturn their preconception that the human heart was in the centre of the chest, even when the evidence was routinely before their eyes, their hands, and their scalpels.
If i was more techy I would get a computer pattern recognision to analyse the photos of craters to get an objective assessment rather than by eye.

> most of the craters are circular, so I guess the hexagonal ones are a minority.
Correct. But there's enough hexagonal and polygonal craters to prompt investigation.

> I don't see any problem with this explanation of why a polygonial crater can form
The basis of modern understanding is the scientific method; I've yet to see lab demostration/test of creation of a hexagonal / polygonal crater by impact. You are ok with this?

Hexagon crater on Mercury

There seems to be a pattern of about 4 sides being well defined as an equilateral hexagon, then 1 or 2 sides being poorly defined.

 

[timmdeeg]

The polygonal planimetric shape of impact craters has been known for a long time, but has not been discussed much in the past. Polygonal craters exist on all kinds of celestial bodies that have fractured rigid crusts. They are also found on the Earth (e.g., Meteor Crater, Söderfjärden). Polygonal craters are thought to have been formed by two possible mechanisms. Simple polygonal craters, such as the square-shaped Meteor Crater, result when the excavation flow opens the crater, tearing the target more easily along pre-existing fractures or other planes of weakness. Complex polygonal craters are supposed to have formed during the modification stage, when rocks of the crater rim slump along the fractures in the target. ...

 

[GregM]

Geographic hexagonal fracture lines. I think this lot played too much Civilization 5. Looking at the Earth's geography and geology, hexagonal fault patterns don't exist.
I don't see any lab model evidence.
Callisto's South Pole

 

[Ibix]

hexagonal fault patterns don't exist.

https://en.wikipedia.org/wiki/Basalt#Columnar_basalt

 

[sophiecentaur]

The basis of modern understanding is the scientific method; I've yet to see lab demostration/test of creation of a hexagonal / polygonal crater by impact. You are ok with this?

I seem to remember that the size of crystals formed depends a lot on the timescale involved; the slower the bigger.
During the formation of a planet/oid there must be a big variety of distances from a star or bigger planet which could, in some instances, produce very big crystalline forms. These could be revealed by impacts. Would such lab tests to check this be easy / possible to carry out? It sounds like an expensive idea.

 

[Drakkith]

The basis of modern understanding is the scientific method; I've yet to see lab demostration/test of creation of a hexagonal / polygonal crater by impact. You are ok with this?

I don't see any lab model evidence.

Hard to build labs that are several kilometers across and in depth that can withstand the impact of a multi-hundred-meter-sized impactor traveling at several kilometers per second.* That's probably the only way you'll get the right scale of size, energy, and depth to do a proper test.

*I guess we could cordon off a section of the surface somewhere for a test, but corralling a meteor is harder than herding cats and a fair bit more destructive to the surrounding environment.

Looking at the Earth's geography and geology, hexagonal fault patterns don't exist.

And yet the researchers disagree with you since they cite it as a possible cause. Well, they cite "fractures or other planes of weakness", not faults, but I'm unsure of the technical distinction between the two or if you really meant to use two different terms. In any case, I doubt these are truly hexagonal since that would imply a singular fracture. More likely the regions of weakness are simply oriented at different angles to each other, and we are simply seeing the ones that happen to end up vaguely shaped like a polygon as 'special' and singling them out.

 

[sophiecentaur]

*I guess we could cordon off a section of the surface somewhere for a test, but corralling a meteor is harder than herding cats and a fair bit more destructive to the surrounding environment.

It's not essential for lab tests to confirm all theories (eg Black Holes do't appear in the lab); all that's necessary is for suitable evidence to be found. But I wasn't suggesting playing with meteors; just suitable lumps of satellite stuff that are no longer useful in their orbits. However, Kinetic Energy being what it is, the velocities available from re-entering garbage would probably not be enough.
But we have already 'explained' to ourselves that the momentum is not relevant so why not just use a massive explosion?

 

[Drakkith]

But we have already 'explained' to ourselves that the momentum is not relevant so why not just use a massive explosion?

There are probably quite a few nuclear blast craters left over from all the tests. Perhaps we could use them?

 

[Frabjous]

There are probably quite a few nuclear blast craters left over from all the tests. Perhaps we could use them?

My second favorite nuclear cratering experiment

Before anyone gets too excited about the shape, it is from 5 detonations.