HiPOD, HiRISE Picture Of the Day Options

[jamescanvin]

And here's a big one. (note this is at 50cm/pixel)

[SteveM]

Abysses! (With scale )

James

They're not abysses, they're qanats. Now we know where to look for the water.

Percival Lowell was right about canals, only they were underground.

Steve

[CosmicRocker]

I guess they are more romantic terms for those so inclined. I thought they were lowly "pits," but how spectacular they are. I must say that the fountain of HiRise and other MRO instrument data recently released has brought me to my knees in tears, so perhaps some artistic license is in order.

I have been trying for a couple of weeks to post some of my favorite crops from these amazing images, but every time I open a new one I find myself getting lost in a never-never land of disbelief. It is all so real, yet unreal. Polar Layered Deposits, alluvial fans, gullies... How about the mega-breccia? That one really freaked me out. Who is waiting for the MRO data from that "light-toned" gully deposit? I so wanted to point out some special places in all of them. I guess I'll settle for posting one tonight.

This highlighted color image from the pole captured my attention. It was kind of like finding an agate in the rough. It is seriously reduced in resolution, and minus a scale bar, but this is one to get in full res.

[rogelio]

MANY thanks for the scale bars, jamescanvin!

Now I can see at a glance that the small "ganats" are the size of a backyard inflatable swimming pool, and the big "ganat" is the size of a city block.

Wasn't that easy?

[Ames]

They're not abysses, they're qanats. Now we know where to look for the water.

Percival Lowell was right about canals, only they were underground.

Steve

"ICEBERG!, right ahead!"
April 14 1912

Could these be icebergs rising above the CO2?

Nick

[CosmicRocker]

That is an interesting thought, Ames. I don't know a lot about the polar layered deposits, but I thought they were composed of layers of water ice, CO2 ice, and aeolian sediments. Your comment caused me to look up the density of CO2 ice, which is reported to range between ~ 1.3 and 1.6 gm/cm^3. So, water ice should be buoyant in CO2 ice.

We know that glaciers of water ice flow at earthly temperatures, but I would assume that flow is slower in current Martian temperatures. I don't know if CO2 ice can flow, but since it is held together by Van der Waals force, it probably can.

I hope some folks who know more about these layered polar deposits comment. There is a lot of thickening and thinning observed in the polar layers recently imaged by HiRise. Much of that appears to be due to depositional/erosional processes, but some of it resembles the density induced flows seen in buried salt layers on Earth, which flow more slowly than ice. I haven't found any diapirs, but this concept is intriguing.

[SteveM]

Another model would be that these are glacial caves and crevasses. (A more serious variant of my original qanat suggestion).

The HiRISE caption doesn't say whether the ice they've imaged is CO2 or Water ice. If the latter, could we have the kind of water flow that creates glacial caves on earth? (subterranean heating coupled with salts producing an anti-freeze mechanism).

On a stream-of-consciousness tangent, is there any research on the physical properties of frozen brines of various kinds of salts? At Martian temperatures, we could see all kinds of intriguing solids that are never solid in ordinary terrestrial circumstances.

Steve

[CosmicRocker]

No doubt the pits and pit-chains are something like terrestrial glacial caves and crevasses. Something that was once there is now gone. Coincidentally, the main JPL site is running a feature about some studies of moulins in Greenland glaciers.

I just wanted to clear up some potential confusion I may have caused with my earlier post. I was talking about some of the thickening and thinning of the layers seen in the HiRise image of the polar layered deposits, not the pits. Some of it looks flow induced to me.

I tried earlier to find some physical property information about CO2 and H2O ice, but didn't find much that I could relate to shear or tensile strength. Surely it is out there somewhere. As for frozen brines, I don't know.

[Nix]

Tumbling boulders;

http://www.awalkonmars.com/PSP_001415_1875..._crop100per.jpg

also in color from HiRise website;

http://hiroc.lpl.arizona.edu/images/PSP/PSP_001415_1875/

Nico

[CosmicRocker]

Those are awesome, Nico. Thanks for posting that, and for the crop.

[Ant103]

Tumbling boulders;

In the first time, I think that was car tracks on the sand! Very strange how geomatric are these features.

[Stu]

In the first time, I think that was car tracks on the sand! Very strange how geomatric are these features.

Oh god, Hoagland is just going to LOVE these hi-res images... he was bad enough when things were blurry, now we can see all this fine detail he'll be telling people on Enterprise Mission (oh, and by the way, does anyone else hate the fact that he's hijacked the name of the most famous, most noble starship ever? It really, really grates on me!!!! Sorry, rant over!) that every tumbled boulder track was made by a golden-sailed martian sandship hissing across the plains....

[ngunn]

I notice that some go straight but with bounces while others go in curves. I wonder if this is because most of them are flattish slabs? The straight bouncy tracks could be due to slabs rolling face-over-face while the curves are made by slabs rolling wheel-fashion on their edges.

[Nix]

Something to think about ngunn...though the local geometry might hold a lot of 'variables'.

Nico

[ngunn]

the local geometry might hold a lot of 'variables'.

Nico

Sure. It could be that the straight ones are more like cubes or irregular spheres while the curves could in principle be produced by tapered spindle shapes, but I do think wheel-like behaviour is the most likely explanation for the curves because the curves seem to tighten up as the objects lose momentum - exactly like a wheel, or coin.