Just wanted to add my own wishes to everyone here to have a wonderful Christmas and a happy New Year. Also want to share my hopes for peace on Earth... and Mars... and Mercury... and Venus... and Saturn...

-the other Doug

Very dark to black sand dune structures aren't all that uncommon on Mars. In fact, we've studied one closely -- El Dorado at Gusev.

It would seem that certain Martian wind shadows set up a process that sorts for the grain size of the black sands.

-the other Doug

I agree that the "rock bubbles" are an exciting find. (I still think we're primarily looking at "rotten" rocks a la Pot o' Gold, but I'm sure Curiosity's studies will help constrain that.)

However, we've had a certain amount of the effect of people looking for something and suddenly seeing it everywhere. Specifically, seeing "bubbles" in the sides of the rocks.

Round (or round-ish) holes in rocks, even those showing a remnant crust around or still inside the hole, actually tend to fall in one of the following well-known and well-understood categories:

1) Vesicles in igneous rocks. These are gas bubbles that existed in the original melt that caused voids in the rock as it cooled. (Note that the original melt could be either erupted basaltic lava or splash-emplaced impact melt; from a rock-creation standpoint, both processes form nearly identical-looking igneous rocks.) Depending on the composition of the gasses that created the vesicles, you can even get a slightly hardened surface on the inside of the vesicle as compared to the solid rock; as such a rock erodes, the vesicles are uncovered and sometimes the slightly harder inner "rinds" take longer to erode than the surrounding rock. Et voila, a "bubble" in the side of an igneous rock.

2) Clasts in clastic rocks. (Yeah, I know, that's a self-circular-defining phrase. A clastic rock is any rock composed of clasts held in a matrix. This would include conglomerate rocks, breccias, and welded tuffs.) The clasts in a clastic rock can be either harder or softer than the matrix (sometimes both in the same rock). If a clast is more easily eroded than the surrounding matrix, you get holes in the sides of the clastic rocks. If the matrix is softer, you get bumps along the sides of the rock. And, of course, if the matrix is softer, at some point it erodes out from around the clast, which falls to the ground and leaves a hole in the side of the rock, something we saw pretty clearly at Hottah. As with vesicles, some of the processes of clast entrainment (i.e., the processes by which the small rock clasts are surrounded by and cemented into the matrix) can result in chemical and thermal interactions at the matrix/clast boundary that can create a hardened contact. In other words, you could have clasts that open up and erode out but leave a thin rind behind for a while.

When I recall these facts and look at the rocks in detail again, I find that I don't see much unusual in terms of "bubbles" on the rocks themselves. The bubble phenomenon seems to manifest mostly in rocks sitting out on a relatively flat surface somewhere. I think the bubble-shaped holes in the rocks are pretty apparent on a lot of martian rocks, and to a very great degree fall into the vesicular or clastic rock categories.

-the other Doug

That depends on what filled the crater after it was formed. The floor is obviously made of some kind of fill -- Gale at present is nowhere near as deep as it would be if the floor was the original impact-melt-lined bowl.

If water and wind transport caused the entire crater fill, then at the very beginning of the process, you're right, it would be filling directly onto a brecciated floor covered by a relatively thin layer of impact melt. However, if the impact opened up a vent to an active lava conduit, the floor of Gale could have been filled in with a solid basaltic plug before the slower deposition and deflation processes began to carve and rearrange what was left. I get the feeling this is the kind of start point the model you mention is positing.

-the other Doug

I would normally not waste anyone's time with the recently debunked craze over 12/21/12 being the End of the World, but two things I heard lately, I thought, were worth sharing:

1) A friend of mine said the ultimate irony would be if, at the stroke of the solstice, every single human being of Mayan extraction simply vanished off the face of the planet, poof!

2) Another friend said he was trying to organize a movement wherein everyone would rush out of their homes on the morning of 12/22/12 and scream joyously "He did it! The Doctor saved us!"



-the other Doug

Well -- there are a lot of reasons why rocks crack, ranging from shock to thermal cycling, both with and without water involved. Polygonal cracking tends to be caused by rock mass shrinkage (for example, when one-wet rocks or ground mass become dessicated) or thermal cycling. But the simple presence of cracked rocks doesn't always easily identify the exact process that caused the cracks.

-the other Doug

Good concept. However, since you'd have a wide variety of approach trajectories for these various NEOs, any such on-demand intercept spacecraft would likely need to start out its mission with an awful lot of delta-V available in its fuel reserves. With enough energy packed into the fuel tanks, and with possibly a small fleet of such interceptors, you could use some to perform high-delta-V intercepts once or twice in their lifetimes, and others to perform low-delta-V intercepts many times.

Not only would this be a good way to collect data on the various NEOs that pass through the neighborhood, it would be really good operational experience for deploying a small fleet of interceptors whose purpose is last-minute trajectory deflection on objects that are spotted late and could impact Earth. We obviously don't have good or proven strategies for last-minute deflection technology at the present time, of course... but by the time we decide what measures would be effective, we would have a lot of good operational experience at deploying on-demand spacecraft to intercept approaching objects.

-the other Doug

Yep, very important mission, and the logo is really sweet.

However -- since NASA decided to name the impact point(s) after Sally Ride, I guess I expected to see some nod to the "Sally K. Ride Impact Site" in there somewhere. Not sure how you'd do it, though.

I think, however, that I'll refer to it as Ride Landing, since "Impact Site" makes it sound a bit like ol' Sally was trying to land her spacecraft, but let the delta-V get a little out of control...

-the other Doug

Yeah, it's mostly media hysteria. The headline on the Cleveland Leader article is factually incorrect, while the space.com article only sensationalizes things a little bit.

From what I've seen, this issue isn't expected to occur until well into an extended mission. It seems the particular bond that, it is suspected, will fail is something that will eventually fail due to repeated use of the drill. A pneumatic drill is subject to a certain level of vibration, after all.

In addition, while both articles called out Rob Manning's description of what an unprotected electrical short could do to MSL's electronics, they relegate to the very end of the article details on a workaround that may completely resolve the issue if/when it does occur.

So, yeah -- mostly media hysteria, I agree.

-the other Doug

One other thought has occurred to me for the origin of these bubbles.

There seems to be a fair amount of agreement that the current surface has been deflated from previously-covering layers. We also know that Mars has a quite healthy impact flux.

Could these be remnants of small impact structures that were originally formed in a surface that has since been deflated, leaving only the small semi-spherical dyke of impact melt intact?

I admit, with a lot of these features occurring in the same surface horizon, you would have to posit a large number of relatively contemporaneous primary impacts into the now-deflated surface, and that does beg an explanation.

I've just learned that when you find any roughly circular structures on a surface that sees a significant impact flux, you need to at least consider an impact origin for them.

-the other Doug

They remind me, in many ways, of Pot of Gold, just more completely evacuated of the base rock (and a more complete decomposition of the indurated rind, leaving only that part protected by the proximity of the ground beneath it).

In most of the examples people have highlighted here, it looks like the base rock has been completely eroded away and the remnant rind is filled in with the same kind of soil or rock that covers the surrounding surface. However, in at least one example, it looks as if some of the base rock is still in place as crumbled-looking fragments -- that's the one that most reminds me of Pot of Gold. It also seems to be sitting up on top of the rock on which it sits and not as embedded in it as the other examples.

I'd be really interested in some ChemCam shots at something like that, where we could see if there's a difference between the base rock and the harder indurated rind.

-the other Doug

Edit -- here is the best view of the one I thought looked like it was sitting more on top of the surface, and where it looks a little like crumbles of the base rock might be sitting just inside the rind. It's the rearview mirror shot:

http://mars.jpl.nasa.gov/msl-raw-images/pr...RHAZ00307M_.JPG

Since there was more hydrazine left in the descent stage tanks on Curiosity than expected, is it possible that the 2020 rover could be upgraded somewhat in weight? Or do the other EDL phases constrain the total mass for this landing system such that we'll need to end up with a rover pretty much the same weight as Curiosity?

-the other Doug

Well, yes-but. See, one of the big things that is happening in the Mars Exploration Program is that we're developing a recognition of "signatures" from orbital data to identify the kinds of rocks and soils we would see on the surface. The landers are providing ground truth for these initial attempts at identifying these signatures and interpreting them correctly.

What I would more expect than a revisit to Gale or Meridiani would be the identification, based on ground-truth-refined signatures seen from orbital data, of other locations that not only offer "jackpot" samples (as defined by correlations between MER/MSL data and orbital data) but also samples of other materials that are tempting but for which we have not yet achieved ground-truth correlations.

I think this is going to play out differently from "OK, Curiosity found our samples, let's land another MSL there to gather 'em up." I'd bet we will find another location where our jackpot signatures are strong but which also features evidence of even other fascinating sample options, and send an MSL with a caching system to that location.

-the other Doug

The idea of caching samples on a rover for a sample return mission (Mars Sample Return, or MSR) is that the rover would be the mobile part of the operation, picking up samples and inserting them into a cache that is designed to be transferred into the MSR Earth return capsule. The cache unit and transfer mechanism to place the cache unit into the MSR capsule are not yet designed. Of course, neither is the MSR return capsule.

The MSR lander, with its ascent stage and Earth return capsule, is going to be heavy, likely the heaviest thing we will try landing on Mars up to that time. The caching and transfer systems will almost definitely have to be landed separately, as part of the rover that collects the samples.

However the design evolves, it will definitely be more involved and complex than dropping rocks on the rover deck and trundling them up to the MSR lander. I envision an encapsulating system on the rover and a simple transfer of sample cans into well-fitting receptacles in the Earth return capsule. That will all have to be designed and implemented. So, no way either of the active rovers on Mars right now would be able to support MSR sample caching.

-the other Doug

Well... perchlorate was one of the options that was being discussed at the time of the original GCMS experiments on Viking. The phrasing I recall is that the time-release experiment data fit well with a Martian soil rich in "super-oxidants," and one of the super-oxidants that headed the list was perchlorate. I believe the presence of chlorine in some of the evolved gasses seen in the Viking results is what led to that speculation, 36 years ago.

I don't have any articles of the time in front of me, but I am very confident of my memory of the "super-oxidant" reports.

-the other Doug

Say, guys? Where'd y'all put that swear jar?

Incredible work, Bjorn! Sort of puts paid to any question that the clouds are casting shadows, doesn't it?

-the other Doug

And yet the media still hear what they want to hear...

Huffington Post - Curiosity Finds Evidence of Organics on Mars

sigh...

-the other Doug

If I don't say this as smoothly as I might otherwise, please forgive me. The thought racing around my brain delves into areas of physics about which I'm not completely confident.

First, it has struck me that dust devils form more easily on Mars than they do here on Earth. Considering how thin the air is and how cold the overall environment is, you would think there would be more energy available on Earth for such vortex formation than on Mars.

But, I says to myself -- Mars spins around its axis at roughly the same speed as Earth spins about her own axis. But Mars is significantly smaller. Its surface is rather closer to the center of rotation than is ours.

Would this not, based on conservation of angular momentum, mean that the coriolis force would be noticeably stronger on Mars? The spinning skater spins faster and faster as her arms are drawn towards her, and on Mars the difference in rotational speed between me and the spot 10 meters to the north or south is greater than at the same distance on Earth. And, if I understand the coriolis force correctly, it is this difference in rotational speed that drives everything from typhoons to dust devils to the swirl of water running down the drain.

So -- if I'm reading this right and the coriolis force on Mars is noticeably greater than on Earth, encouraging a lot more atmospheric vortex formation, how would this affect simple aeolian erosion patterns on an early Mars with a much thicker atmosphere than now?

Consider that in 6mb air pressure a modern Martian dust devil can pick up and entrain a pretty impressive mass of dust and pebbles. This process keeps much of the Martian surface swept clean of the ubiquitous orange-brown-yellow dust, the darker gray rock beds thus exposed forming the dark markings visible in telescopic images of Mars for more than a century.

How much more erosive would a thicker atmosphere be, if an increased coriolis force makes it tend to form vorteces at every opportunity?

This relates to the previous posts thus -- imagine Gale crater nearly filled with some form of fill. Then imagine a racetrack wind pattern running around inside the crater walls, breaking up into hordes of large dust devils which, due to the thicker air, are able to pick up tons of material and toss it high into the air?

You'd have a pretty dusty atmosphere all the time (which would tend to cool the surface, I imagine), but such a wind pattern might be able to deflate an *awful* lot of material out of a crater in a pretty short time, at least in geologic terms.

Maybe it was such a dust devil breakout phase that deflated a lot of crater fill on Mars?

-the other Doug

I can't say when I would be able to order something, but I would bet that the MER-A and MER-B patches (Daffy and Marvin) would be popular amongst UMSF'ers. T-shirts, mugs, etc., with either or both of those patches on them would be really kewl, I think.

Just my $.02...

-the other Doug

Yep, Mars' surface is primarily basaltic, no doubt. And like the Moon, much of the original crust has been highly brecciated by the Late Heavy Bombardment (the "event" which likely resulted in the Gale impact, among tens of thousands of other impacts of similar size).

Analysis of basalts, where they were emplaced, would give us a nice feel for what was happening in Mars' mantle while the majority of the basaltic eruptions occurred and the basalt was emplaced on the surface. Sort of a snapshot of the mantle during the period(s) of heavy volcanism. However, it is the alterations and re-depositions of that basaltic set of "building blocks" that tell us about the climate and conditions on the surface after the basalts were originally emplaced.

So... Gale is not a good place at all to survey variations in directly emplaced basalt flows. The occasional unaltered chunks of basalt lying on Gale's floor were likely transported from somewhere else (be it a few kilometers to hundreds of kilometers from where a rock might rest right now). It is, however, a wonderful place to look at the history of re-deposition and alteration of rock beds (and even deflation of covering beds), much of which (it seems to me) has to have happened when the alteration, deposition and deflation processes that went on were far more active than they are now.

Since one of the main purposes of Curiosity is to try and characterize those processes (because those processes, once understood, then highly constrain the climate and environment in which they occurred), Gale is a very good place. Precisely because this is a place where we can study the history of those processes and try to understand them.

-the other Doug

Well... the one end of the depression that is obvious in the most recent pans that have been assembled, here, looks rather circular. Anything that describes a partial or complete circle on Mars, with its higher impact rate than we are accustomed to on Earth, could be the remnants of an impact crater. The flow lines etched into the rock working into the depression could just be the result of eons of aeolian modification.

However -- and this is a big however -- the overall morphology of the region is indicative of alluvial activity, i.e., modification from flowing water. So, even though the edge of this depression is circular and may still represent the remnants of an impact crater, with the clues to alluvial action we can see in the aerial images, it looks to me that the initial modification of the terrain is more likely from water flowing and then ponding in the topographic low point of the depression. Multiple episodes of flash flooding, or continuous drainage from the central mound, could have resulted in the patterns we see.

In any event, the original forces that carved the topography here at Glenelg has since been modified by many, many eons of aeolian erosion since the last of the flowing water was seen here.

-the other Doug

Sorry for the bump, but I do believe this question belongs in this thread.

So far in the short traverse that Curiosity has completed to Glenelg, we've seen some pretty uneven terrain that, in places, is rather heavily rock-strewn. Perhaps enough to have caused some issues at touchdown had the rover landed in some of the spots we've passed.

That said, had MSL landed exactly in the center of its planned landing ellipse, from what we can see in MRO images and can infer to ground conditions based on the traverse thus far, does anyone think the terrain could have caused issues on landing?

I know that the floor of Gale is turning out to be a lot more textured and non-flat than I would have expected from the pre-landing imagery.

-the other Doug

We either have very few UMSF'ers on the U.S. east coast, or a lot of stoic people who rode through Sandy without being too badly affected, or we haven't yet heard from some of our number who have had no power and/or internet access all week.

To all who came through it and all who may be rejoining us soon, good luck and may the multiverse's great deity, Mr. Murphy (he of Murphy's Laws) look kindly on you in these stressful times.

-the other Doug

Exactly, Phil -- what I just called alkali feldspar is the pinkish stuff you find in granites. Of course, on Earth these are formed as a result of subduction, with various rock types including plagioclase being altered under high heat and pressure in the presence of water after the crust has been subducted and then re-exposed by tectonic processes. It would be quite revealing if we were to find significant orthoclase-type feldspar or full-on granitic rocks on Mars, as that would tend to indicate a period of subduction and re-exposure sometime in Mars' past.

-the other Doug

I hear you, John. I guess I ought to have stated my thought by saying I wonder if the source is plagioclase or alkali feldspar? The former is found both as laths within basalt (at least it is on Earth and on the Moon), and as purely anorthositic rock. Alkali feldspar is water-altered and is found (again, at least on Earth) in granitic rock.

However, as I noted in a response to Phil a while back, when you find plagioclase in basalt it is usually in the form of little, almost feathery intrusions in the basalt called laths. As I understand it, this is due to a plagioclase component in the lava melt which cannot mix with the pyroxene and/or olivine components of the lava, and it just solidifies in place in the same distribution found in the original melt, as the strings, strands and thin layers of the lighter, more aluminous plagioclase floated and were moved about as the original melt convected, moved and flowed. (I think of it as freezing a glass of water very quickly after trying to stir in a liquid that won't mix with the water; the non-miscible liquid will form flow structures within the water, which are then frozen into the ice.)

While these laths are not always highly identifiable in macroscopic images, they're usually fairly easily seen when you look with any reasonable magnification. I know I've looked for this kind of lath structure in the various basalts we've seen over the course of 36 years of Martian surface exploration, and I've not seen anything I can definitely say is a lath structure that would say for certain that Martian basalts have a significant feldspathic content.

I'm not saying it isn't there, I'm just saying that I've not seen it. Of course, it may be I wouldn't recognize a lath structure in situ -- I normally see it best in thin-section slides, after all. And, of course, I've not seen the basalt elemental abundance results of all of the MER sensors, at least not directly. So, I certainly can't be sure. I'd just be interested in seeing whether or not MSL finds a significant feldspathic component in the intact basalts it studies.

-the other Doug