by rstevenson » Sat Aug 13, 2022 5:33 pm
Holger Nielsen wrote: ↑Sat Aug 13, 2022 7:24 am
This is an intriguing image. There seems to be no exterior crater wall. Perhaps this is due to the low gravity on Mimas, resulting in permanent ejection of all material which was blown out at the impact?
Also, the crater has a steep, smooth wall. Is the reason, that the inside of the crater at some time sank back into the interior, and if so why? Or was the crater left by the impact gradually filled with water from the interior, which froze solid before reaching the surface? But in that case, why is there a central mountain?
I wonder if you’re seeing it in a sort of reverse 3D. I sometimes have a very hard time seeing the correct 3D effect in, for example, some Mars images from orbit, but if I import the image to an editor and rotate it 180* it clicks into place. There is certainly an exterior crater wall, most easily seen at the top of the crater in this image, the silvery white areas. They slope down (physically and in this image) to the crater floor.
[ later edit ] … Ah, I see what you mean. The crater walls don’t seem to have a lip at the top, relative to the surrounding terrain. I think I can see such a lip in a few areas, but not generally or obviously. So, yes, in such a small object I guess the low escape velocity allowed a great deal of excavated material to be ejected away from the impact site, some of it likely landing later all over the poor moon.
Rob
[quote="Holger Nielsen" post_id=325037 time=1660375454 user_id=143698]
This is an intriguing image. There seems to be no exterior crater wall. Perhaps this is due to the low gravity on Mimas, resulting in permanent ejection of all material which was blown out at the impact?
Also, the crater has a steep, smooth wall. Is the reason, that the inside of the crater at some time sank back into the interior, and if so why? Or was the crater left by the impact gradually filled with water from the interior, which froze solid before reaching the surface? But in that case, why is there a central mountain?
[/quote]
I wonder if you’re seeing it in a sort of reverse 3D. I sometimes have a very hard time seeing the correct 3D effect in, for example, some Mars images from orbit, but if I import the image to an editor and rotate it 180* it clicks into place. There is certainly an exterior crater wall, most easily seen at the top of the crater in this image, the silvery white areas. They slope down (physically and in this image) to the crater floor.
[ later edit ] … Ah, I see what you mean. The crater walls don’t seem to have a lip at the top, relative to the surrounding terrain. I think I can see such a lip in a few areas, but not generally or obviously. So, yes, in such a small object I guess the low escape velocity allowed a great deal of excavated material to be ejected away from the impact site, some of it likely landing later all over the poor moon.
Rob