Starship Asterisk*

by **Thor127** » Wed Mar 12, 2014 1:39 pm

It appears to be a sink hole. The lack of ejecta seems to rule out an impact crater.

by **geckzilla** » Mon Mar 10, 2014 3:48 am

Pits likely formed as a result of multiple collapsed sections of lava tubes on the moon:
http://www.nasa.gov/mission_pages/LRO/m ... chain.html

A similar argument about the possibility of impacts is discussed. This example is much more clearly along some linear geological (selenological?) feature.

by **neufer** » Mon Mar 10, 2014 3:36 am

geckzilla wrote:
rstevenson wrote:
Even if an impact is a simpler explanation? It gives us the rim and the hole too.
It could be a crater, sure, but the rim to me looks wind blown and the surrounding ground texture also looks to me something like some kind of soil fine enough to be blown. So visual evidence of a crater could be obliterated by erosion. I find it difficult to determine if it is just a place where a lava tunnel was weak in the ceiling or if an impact was required to form it. It seems too clean to be a crater.

Assuming that the dunes on the left of the crater are longitudinal Seif dunes the prevailing winds probably blow from left to right. Hence, the right crater rim will end up being pelted by a turbulent sheet of light soil/sand flying off the left crater rim. This turbulent sheet would probably deposit a horizontal dune along the right crater rim followed by horizontal dune ripples.

by **Nitpicker** » Mon Mar 10, 2014 3:06 am

It seems unlikely (to me) that any impact capable of forming this depression, did not completely obliterate the cavern below. And the impact is unlikely to have occurred before the creation of the lava tube, since the entire mountain is formed by lava flow (if I understand my volcanology well enough).

by **geckzilla** » Mon Mar 10, 2014 2:58 am

rstevenson wrote:Even if an impact is a simpler explanation? It gives us the rim and the hole too.

Rob

It could be a crater, sure, but the rim to me looks wind blown and the surrounding ground texture also looks to me something like some kind of soil fine enough to be blown. So visual evidence of a crater could be obliterated by erosion. I find it difficult to determine if it is just a place where a lava tunnel was weak in the ceiling or if an impact was required to form it. It seems too clean to be a crater.

by **Nitpicker** » Mon Mar 10, 2014 2:51 am

From what I can tell, I think this depression is on the NE slope of the volcano and the image is oriented with North up. (Someone please correct me if I am wrong.) So, the volcano's slope is falling from bottom-left to top-right in the image. The top-right of the edge of the depression is therefore a slight crest, and may be a natural place for a dust dune to form.

by **rstevenson** » Mon Mar 10, 2014 2:39 am

Even if an impact is a simpler explanation? It gives us the rim and the hole too.

Rob

by **geckzilla** » Mon Mar 10, 2014 2:27 am

Rob, I would guess that the rim could be caused by prevailing winds. It is slight enough. Something like a dune formation.

by **rstevenson** » Mon Mar 10, 2014 2:21 am

People keep talking about this as if a hole just appeared in the roof of a cavern and loose material fell in, making a crater. But that does not explain the rim around the crater. The only way you get a rim is when a rock of some sort crashes into the planet. In this case it happened to hit the side of a volcano where there are lava tubes, and it punched a hole in one of the tubes. And yes, probably some material then slid down the sides of the crater into the hole. But it's still, I'm sure, an impact crater.

Rob

by **Nitpicker** » Mon Mar 10, 2014 2:05 am

If the depression is volcanic and caused by subsidence, would it be more correct to refer to it as a caldera and not a crater?

Note that the depression is ~300 times smaller than the 47km diameter, 5km deep caldera at the peak of Pavonis Mons. Also note that the side slopes of the volcano are rather mild, 7% on average (4° incline). Whilst I'm not sure I'd like to live/exist/barely survive that close to a massive shield volcano -- however lacking in recent activity -- I suppose it might be warmer than some parts of Mars.

by **zaqs** » Mon Mar 10, 2014 12:38 am

Chris Peterson wrote:
Guest wrote:I do not understand the illumination of this picture.

The external shadow of the cone is on the same direction as the illuminated bottom of the hole. It is as there are two sources of light.
I think you're being fooled by the famous concave/convex optical illusion. There is no cone here. The hole is at the bottom of a depression.

I'm agree with you, the shades are not coherent for a cone (and i'm not a troll

)

by **Beyond** » Sun Mar 09, 2014 10:46 pm

Chris Peterson wrote:
Beyond wrote:The caption refers to it as a "cone", not a depression. A cone is what i see. It would seem that anything landing inside of the cone, would end up sliding down through the hole at the bottom, just as on earth, anything entering an Antlion's cone trap, would find itself heading downward towards the Antlion that's waiting down in the center of the cone.
I don't see any reference in the caption to cones. It's called a hole surrounded by a crater. Craters of this size have somewhat conical interiors. The important point is that the feature is concave- it is a surface depression. The earlier reference to "cone" appeared to be suggesting the feature is actually convex- a hole on the apex of a hill.

Dang!! I must be older than i think i am. After i saw you use the word "depression", i went back through the caption and couldn't find "depression" anywhere, but did see the word "cone".
Now that you've replied with not being able to find the word "cone" anywhere in the caption, i just went back through it and can't find it either and also still can't find "depression".
I figure this tired old brain did a short-cut and translated 'crater' to 'cone' and neglected to tell me.

by **Chris Peterson** » Sun Mar 09, 2014 10:20 pm

Beyond wrote:The caption refers to it as a "cone", not a depression. A cone is what i see. It would seem that anything landing inside of the cone, would end up sliding down through the hole at the bottom, just as on earth, anything entering an Antlion's cone trap, would find itself heading downward towards the Antlion that's waiting down in the center of the cone.

I don't see any reference in the caption to cones. It's called a hole surrounded by a crater. Craters of this size have somewhat conical interiors. The important point is that the feature is concave- it is a surface depression. The earlier reference to "cone" appeared to be suggesting the feature is actually convex- a hole on the apex of a hill.

by **Beyond** » Sun Mar 09, 2014 10:14 pm

The caption refers to it as a "cone", not a depression. A cone is what i see. It would seem that anything landing inside of the cone, would end up sliding down through the hole at the bottom, just as on earth, anything entering an Antlion's cone trap, would find itself heading downward towards the Antlion that's waiting down in the center of the cone.

by **neufer** » Sun Mar 09, 2014 9:59 pm

Click to play embedded YouTube video.

Geckzilla sliding down the sides and falling into the thing

geckzilla wrote:
The photo is abundantly clear to me. I don't think I could understand it much better without sliding down the sides and falling into the thing.

One thing I have wondered about this is whether there is a conical pile of soil at the bottom of the hole to match all of the displaced material above. That could be one reason why the light inside the hole looks a bit darker. Not only is there less light but it could be the shaded side of a pile of soil.

It's just Corvettes all the way down:
http://www.usatoday.com/story/news/nati ... e/5417171/

by **geckzilla** » Sun Mar 09, 2014 9:30 pm

Guest wrote:Yes, I assumed the other variant too, but if this is a depression, the light is consistent, but the semicircular shadow looks kind of weird. A better resolution maybe will clear away my confusion.

The photo is abundantly clear to me. I don't think I could understand it much better without sliding down the sides and falling into the thing. One thing I have wondered about this is whether there is a conical pile of soil at the bottom of the hole to match all of the displaced material above. That could be one reason why the light inside the hole looks a bit darker. Not only is there less light but it could be the shaded side of a pile of soil.

by **Guest** » Sun Mar 09, 2014 9:18 pm

Chris Peterson wrote:
Guest wrote:I do not understand the illumination of this picture.

The external shadow of the cone is on the same direction as the illuminated bottom of the hole. It is as there are two sources of light.
I think you're being fooled by the famous concave/convex optical illusion. There is no cone here. The hole is at the bottom of a depression.

Yes, I assumed the other variant too, but if this is a depression, the light is consistent, but the semicircular shadow looks kind of weird. A better resolution maybe will clear away my confusion.

by **Chris Peterson** » Sun Mar 09, 2014 8:03 pm

Boomer12k wrote:After clicking on the photo....and magnifying the view.....I think we are looking at an illusion. I don't think this is a cavern....I do not see a wall going down into anything....I see a floor with a crescent moon shadow, and a part of the floor of the crater....I don't think we are actually looking inside something.

This is no illusion. There are other images of the same thing, taken under different lighting. You don't see any walls because they are well away from the hole, out of view. This is a hole in a roof of the cavern, not a well-shaped hole.

by **Boomer12k** » Sun Mar 09, 2014 7:53 pm

Humans or Rovers or Robots....they are going to have to watch out for the SARLACC down there!!!!!!!!

After clicking on the photo....and magnifying the view.....I think we are looking at an illusion. I don't think this is a cavern....I do not see a wall going down into anything....I see a floor with a crescent moon shadow, and a part of the floor of the crater....I don't think we are actually looking inside something. The EDGES of the bottom are too consistent...and do not appear to drop into anything....
In other words...it is like a Frozen Lake at the bottom...and what we see is Shoreline and contrast....
Just my observation.

I do observe, that if you look long enough...it can change appearance to look LIKE A CONE...and not a crater....but I think that too is an illusion, as the upper right shadows are on the outer edge where they should be, while the lower left, has few shadows....
I think the light source...is from the lower left....

:---[===] *

by **PacRim Jim** » Sun Mar 09, 2014 7:40 pm

Ant lion ?

by **neufer** » Sun Mar 09, 2014 5:56 pm

Steve Dutch wrote:
The circular "crater" around the hole is obviously due to unconsolidated material falling into the hole. There's even a slightly more durable layer visible about a quarter of the way down. The slope is about 100 meters wide (assuming the central hole is 35 meters in diameter) so if the angle of repose is 30 degrees (a typical value), the blanket of unconsolidated material is about 58 meters deep. Multiple images under different lighting can probably pin down the exact slope and perhaps provide clues about the mechanical properties of the sand.

What is that "slightly more durable layer visible about a quarter of the way down"?

A volcanic eruption?

http://www.tulane.edu/~sanelson/Natural_Disasters/volclandforms.htm wrote:
<<Cinder cones are small volume volcanic cones consisting predominantly of tephra that result from strombolian eruptions. They usually consist of basaltic to andesitic material. Slopes of the cones are controlled by the angle of repose (angle of stable slope for loose unconsolidated material) and are usually between about 25º & 35º.>>

http://en.wikipedia.org/wiki/Angle_of_repose wrote:

Code: Select all

Material (condition)   Angle of Repose (degrees)
--------------------------------------------------------
Coconut (shredded) 	    45°
Bark (wood refuse) 	    45°
Flour (wheat) 	         45°
Chalk 	                 45°
.................................
Sand (wet) 	            45°
Sand (dry) 	            34°
.................................
Earth 	               30–45°
.................................
Gravel (loose dry) 	  30–45°
Gravel (natural w/sand) 25–30°
.................................
Clay (dry lump) 	     25–40°
Clay (wet excavated) 	  15°
.................................
Ashes 	                 40°
Snow 	                  38°
.................................
Clover seed 	           28°
Wheat 	                 27°
Urea (Granular) 	       27°

by **Steve Dutch** » Sun Mar 09, 2014 5:12 pm

The circular "crater" around the hole is obviously due to unconsolidated material falling into the hole. There's even a slightly more durable layer visible about a quarter of the way down. The slope is about 100 meters wide (assuming the central hole is 35 meters in diameter) so if the angle of repose is 30 degrees (a typical value), the blanket of unconsolidated material is about 58 meters deep. Multiple images under different lighting can probably pin down the exact slope and perhaps provide clues about the mechanical properties of the sand.

by **Guest** » Sun Mar 09, 2014 4:59 pm

No need to speculate about the circularity of the hole, both large
http://gizmodo.com/5551916/the-gates-of ... -guatemala
and small
http://www.cumberlandnewsnow.com/News/L ... r-Oxford/1

But why a crater, most seem to be holes, with near vertical sides?
John

by **neufer** » Sun Mar 09, 2014 4:46 pm

Click to play embedded YouTube video.

Beyond wrote:
And that sometimes, have up-dated information also.

These pits are therefore prime targets for possible future APODs.

Beyond wrote:
I'm waiting for the "Icy Finger of Death" to come around again.

I'm waiting for the "The Flying Fickle Finger of Fate Award" to come around again.

by **Beyond** » Sun Mar 09, 2014 4:12 pm

And that sometimes, have up-dated information also.

I'm waiting for the "Icy Finger of Death" to come around again.

Starship Asterisk*

APOD: A Hole in Mars (2014 Mar 09)

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