Comments on: A lunar crater is graben the spotlight

By: James Kottenstette

James Kottenstette — Fri, 14 Sep 2012 00:44:48 +0000

I am not convinced that the evidence cited proves that the crater is younger than the graben. Look at the “small craters” along the sunlight terminus near the bottom of the graben: I think you will recognize that these craters are really boulders! boulders that reflect sunlight where craters would be totally dark. Whether this is true or not, I can find no reason to believe that the walls of the graben did not slowly form later as the (graben) surface showing the rays simply sagged when the graben subsided. You can see a swam of what must be smaller boulders clinging to the bright side of the graben (between 1 and 2 o’clock.) I would argue the the boulders simply collected at the bottom as the graben deepened; hence the crater is older.

By: Bipedal Tetrapod

Bipedal Tetrapod — Wed, 12 Sep 2012 21:32:18 +0000

@A.J.Rimmer
Doesn’t even take 180 degrees. As soon as I tilt it so the graben passes vertical – maybe 25 degrees, then it clicks. And I can see it after that when returned to normal. Just an interesting neurological phenomenon.
I’m used to looking at the moon under all kinds of illumination, but somehow looking through an eyepiece doesn’t give me the same “processing error” as looking at a photograph.

By: Another Phil

Another Phil — Wed, 12 Sep 2012 19:28:20 +0000

@9. Bipedal Tetrapod . Don’t worry, my brain is doubly stupid as I see it as a crater and a ridge, regardless of the differing illumination. I can see it as a graben but not as a first impression.
I suspect you are used to looking at images of fossils or similar as scientific convention is to illuminate from top left.

By: A.J.Rimmer

A.J.Rimmer — Wed, 12 Sep 2012 15:44:23 +0000

@Bipedal Tetrapod:
“Anyone else have trouble seeing the graben as a depression?”

Right click on image -> rotate image 180 degrees.

You’re welcome.

By: Nigel Depledge

Nigel Depledge — Wed, 12 Sep 2012 08:32:18 +0000

The BA said:

They’re common around young craters; solar wind, later impacts, and even thermal compression and expansion of rocks over the Moon’s day-night cycle eventually erode them away.

Don’t forget the constant micrometeorite bombardment.

Or do you include that within “later impacts”?

By: Nigel Depledge

Nigel Depledge — Wed, 12 Sep 2012 08:30:58 +0000

The BA said:

. . . it is, after all, the closest astronomical object in the sky.

[Emphasis mine]

As opposed, presumably, to those much closer astronomical objects under the sea . . . ?

By: shunt1

shunt1 — Tue, 11 Sep 2012 20:11:34 +0000

Amazing image!

Are we sure that it is a graben instead of a rill? Obviously the linear depression can be traced beyond the larger image provided. It just reminded me so much of hadley rill from Apollo 15.

It really does not matter, since the crater if much younger and the rays tell an important story. Anyone notice how the impact was almost vertical?

@Bipedal Tetrapod:

“Anyone else have trouble seeing the graben as a depression?”

Funny, but I have never had that problem.

Perhaps because I grew up with images of the moon since the 1960′s and simply look for light direction first?

I have always found it rather interesting how so many people are almost 3D blind when presented an Anaglyph. Could this be related?

By: Bipedal Tetrapod

Bipedal Tetrapod — Tue, 11 Sep 2012 19:59:36 +0000

Anyone else have trouble seeing the graben as a depression? My brain keeps trying to “assign” illumination from top left, making it look like a ridge, and the crater like a dome.
Stupid brain.

By: Cynipoo

Cynipoo — Tue, 11 Sep 2012 17:39:52 +0000

Very pretty sir

By: Randy A.

Randy A. — Tue, 11 Sep 2012 17:19:40 +0000

A better definition for a graben would be a valley formed between two normal faults. The valley is formed when the land between the faults is dropped down. If the land is pushed up by faulting, it’s called a horst.

Here on Earth, the basin and range province in North America (Nevada, plus parts of the surrounding states) has many grabens, separated by horsts. Perhaps the most famous graben is Death Valley.

Normal faults are a type of dip-slip fault caused by tension. As Phil mentioned (and the linked article discusses), normal faulting on the moon implies that something stretched the moon’s surface — or at least that part of it.