Geomorphology of Gale Crater, Rock on! Options

[Ant103]

Can I ask something ? Not very important, but for me it is. Modifiy the thread from "Geomorphology" to "Areomorphology". As "Geo" came frome "Gaia", the Earth in Greek mythology, so as "Areo" from "Arès", Mars in Greek mythology. But I will understand that's not necessary for the quality of this thread. After all, we use specific word to qualify a day on Mars like "sol" .

[ElkGroveDan]

Not a good idea. The science of geology is what is being discussed here. If you drop one Greek root then you have to drop them all and it starts to sounds like nonsense.

[Guest_Actionman_*]

In this GIF from the above Mr. Anderson and James F. Bell paper they illustrate their view of the basal layer with the possibility of some of which maybe exposed. The examination of any of this is mandatory NMHO. More over I don't think it will be visible. Out of sight out of mind, apparently.

[djellison]

Can I ask something ? Not very important, but for me it is. Modifiy the thread from "Geomorphology" to "Areomorphology".

What would you call Phobos geology. Deimos. Venus. Europa. Dione. Our own Moon. Titan. Nix. Hydra. Tempel 1. Itokawa. There are hundreds and thousands of worlds out there for us to explore, study and understand - and the science we will be practicing is geology / geomorphology / geochemistry etc etc.

Having a different word for the same scientific discipline just because it's a different place is nonsensical.

[Ant103]

Okay, I understand totaly I was just asking. It's funny because in french, when you land a probe onto a surface, we use the word "Atterrissage", with the root "Terre" aka Earth in english. And I'm against using word like "Amarsissage" when you land something on Mars. So then, yeah, I think I was a little too bit enthousiast . Nevermind . And thanks for the answers.

[djellison]

they illustrate their view of the basal layer with the possibility of some of which maybe exposed. The examination of any of this is mandatory NMHO. More over I don't think it will be visible. Out of sight out of mind, apparently.

You know that Basal and Basalt are not the same thing, right?

Not visible? They've already seen it (and attempted to characterise it) from orbit!

From Page 105-106 of their paper ( for those unfamiliar - it's available here - http://www.marsjournal.org/contents/2010/0004/ )
"Light-toned basal unit
The light-toned basal unit is distinguished from the crater floor units by a sharp drop of ~10 m (Figure 34a). The light-toned basal unit has a CTX albedo of up to 0.20, and is primarily composed of fractured rock that in some locations has a subtle texture suggestive of layering (Figure 39b). It has a moderate thermal inertia ranging from roughly 500-540 J m-2 K-1 s-1/2. Mesas of mound- skirting unit are common on top of the light-toned basal unit (Figure 34b), and much of the basal unit is covered by dark-toned mafic dunes. The light-toned basal unit slopes upward in a series of poorly-defined fractured, light-toned layers to form the northwestern side of the light-toned ridge unit (Figure 36a).
Dark-toned basal unit
The dark-toned basal unit (Figure 39) has a higher thermal inertia (~780 J m-2 K-1 s-1/2) than the light-toned basal unit. It has an albedo of 0.15-0.16 and occurs to the southwest of the landing ellipse and the light-toned basal unit. The transition between the light and dark-toned basal units (Figure 40) is sharp and the dark-toned basal unit appears to be topographically lower than the light-toned basal unit. This suggests that it is either stratigraphically lower or that the dark-toned unit is younger and fills a depression that had been eroded into the light-toned basal unit."

Plus - the paper goes on explicitly define a location to visit to help in characterizing it is an important stop on any MSL traverse.

[Guest_Actionman_*]

Basal and basalt are important distinctions both of which are said to scattered on the surface.
Any intact strata should be checked for type. That's all I'm saying.

And no, basal strata in large thick strata placements are not visible from space here at Gale Crater.

[djellison]

You can not scatter 'basal' on the surface. Basal is a descriptor derived from location. The basal unit is the bottom unit. It's not a type of material - it's a placement.

The basal unit IS visible from space. How do you think they mapped it and characterized it from orbit. Read the paper. Heck - just read the description I cited above.

[ngunn]

With the Anderson and Bell diagram easily to hand could somebody clarify for me which geologic unit we actually landed on? Bradbury Landing is located beyond the outer margin of the HTIF yet the rocks on the traverse have been identified as fan deposits. So did we land on a detached portion of LTIF? A patch of MSU?

[djellison]

We're (I think) in the area where the HP, HTIF and LTIF all meet - that three way junction at Glenelg. I'm guessing we landed on LTIF. Broken up fan deposites with lots of sand/fines etc would show up as low TI I would expect ( which is what we've seen) The brighter material to the N/E of us is the HTIF I believe. When we head south, we'll be on HP.

[ngunn]

That's fine for HTIF and HP, but going on Anderson and Bell's map there should be no LTIF at our current location. They have the LTIF mapped to the north of the HTIF while we are to the south of it, hence my query.

http://martianchronicles.files.wordpress.c.../09/figure7.jpg

[JRehling]

I've been thinking that the landing site was HP, having missed the fan, as you say, to the north. But our confusion is, I think, owing to the inherent complexity:

The distinctions we're talking about are not necessarily visible or even rigorously meaningful. Thermal inertia is a property that can vary from place to place on the basis of any combination of changes in composition or fine-scale morphology in potentially-wicked interaction between the visible surface and the near subsurface. Maybe MSL landed outside the area that Anderson and Bell colored as "fan" on their map, but is nonetheless in an area where the fan material is present, but in combination with other stuff so as to give it a different thermal inertial. In fact, there's no logical disconnect between these labels: "high thermal", "fan unit", "hummocky", and "plains" are potentially overlapping in any combination because they four different kinds of property.

I think MSL missed the region that A&B labeled as being the fan, but may in fact have some of that fan material all around, in some fraction, anyway.

On a very similar theme, I was surprised, having read A&B carefully, how difficult I find it to see the units on Mt. Sharp, which seem apparently in the B&W images taken from orbit, in the images from MSL. There are many possible reasons for this, including the viewing geometry, the image properties (such as gamma), my lack of field geography savvy, etc.

A&B did a good job of imposing some logic and order on Gale, but in both the MSL landing site and the distant views of Mt. Sharp, things seem a little more chaotic up-close.

[elakdawalla]

I was having the same issue you were in seeing the units on Mt. Sharp until I realized that most of the interesting stuff -- the clays and sulfates -- is actually in a trough at the base of Mt. Sharp and mostly not visible from where the rover landed.

Working out some comparisons of the A&B units to images from HiRISE and pointing out locations on the landing site panorama has been on my list of blog entries to write for a long time, but it's a big project and I haven't made much progress yet.

[ngunn]

(Replying to JR) All good points. I agree that the views from the ground are taking us into a post-A&B era. But the meeting of three distinct terrain types at Glenelg is most clearly seen in the orbital images so it didn't take Curiosity to show us that.

High thermal inertia is, I think, indicative mainly of a lack of loose cover over the bedrock. In Anderson and Bell that is identified with a particular rock unit, but why would one particular type of rock preferentially remain clear of debris? I think ithe HTI
disribution may be controlled more by the geographical context of the removal process and the ease of removability of whatever material used to cover the bedrock.

EDIT
Emily: good luck with that project - I look forward to seeing the results

[stewjack]

In the conclusion section of the abstact for Anderson and Bell III: Mars 5, 76-128, 2010 open access paper,
there is the following sentence -"Some layers in the mound are traceable for >10 km, suggesting that a
spring mound origin is unlikely."

My understanding of that would be that Mt Sharp was not cemented together by underground (upwelling) mineral water flows during,
I guess, - the period when Gale crater was buried in sediment. Because earlier it is said "The rim of Gale Crater is dissected by
fluvial channels, all of which flow into the crater with no obvious outlet." As well as, I guess, that hot springs would be variable in flow,
time and location? After doing some Googling apparently hot spring can create mounds using nothing but precipitated minerals. However;
I don't now how that would relate to the 10 km layers. Would be enough to say that a mound with many layers wasn't created by hot springs?
Or am I completely misunderstanding what the sentence is trying to communicate?