Welcome Professor "brine splat" Burt, "a chance to ask questions... or raise objections" Options

[nprev]

I don't know if tides could be considered as part of the issue at this point, $0.02. We don't know what the possible depth & volume of any waters @ Meridiani might have been, and of course the only significant tidal influence would be solar...difficult to reconstruct a plausible scenario with the limited data we have.

[dvandorn]

Not to belabor a point, but it gets down to how you exercise the scientific process.

Gravitation, terrestrial crustal movement and even diversification and radiation of species are not theoretical, they are observed phenomenah. They are objectively, empirically observable. The mechanisms involved in how they operate are theoretical. (This is the argument I get into with my girlfriend... )

You cannot open your assumptions so broadly that you begin to treat empirical observations as unproven theories. That sabotages the scientific process and leads to festoons of tin-foil hats...

-the other Doug

[centsworth_II]

You cannot open your assumptions so broadly that you begin to treat
empirical observations as unproven theories.

The festoons are "objectively, empirically observable". The "mechanisms
involved" in how they form are theoretical. I don't think anyone is arguing those
points. I'm curious about what theories are out there concerning how the water
flow (that caused the festoons according to the water flow formation theory)
occurred. Wind? Rising and falling water tables on a slope? Maybe it is no
problem for wind blowing over shallow water to form such festoons. I don't know.

[nprev]

The festoons are "objectively, empirically observable". The "mechanisms
involved in how they form are theoretical... Maybe it is no
problem for wind blowing over shallow water to form such festoons. I don't know.

Yep; there's the real rub: too many undefined variables, and therefore poor constraints on the scope of the problem. We don't know what the conditions were like, and one hell of a lot of legwork is needed to figure that out before even attempting to declare likely explanations for the observations. It does seem as if water was present at some point, but there seems to be precious little objective data that tells us for how long, or how often.

[stevo]

Not to belabor a point, but it gets down to how you exercise the scientific process.

Gravitation, terrestrial crustal movement and even diversification and radiation of species are not theoretical, they are observed phenomenah.

No, they are not. The motion of planets, apples and bits of the Earth's surface are observations, the theories which account for them are theories. Hugely successful, taken as reality (or the best available description of it) in the normal course of science, but still theories. And necessarily open to falsification.

It seems to me that we need to keep this distinction very clear when we are observing a new world where the basic rules of chemistry and physics remain the same, but the situations are different from what we have previously seen on Earth.

Stevo

[dburt]

Thanks for all the thoughtful replies about water flowing over a horizontal surface, in relation to "festoons". I agree such flow is theoretically possible, just not highly plausible (e.g., why don't you see "festoons" everywhere, across the entire area, if there was sheet flow, with no channels?). I'm reminded of the one about the procrastinating student who tells me he wants to take a make-up test because his grandmother died on the date of the first test and I say fine. Then he tells me the same thing again for the second test, and I think, well, okay, but that's kind of a coincidence. This kid is sure hard on grandmas, and he's all out. Then he comes up to me well after the third test and asks for a third make-up, "because my grandmother died". I say, hey wait a minute, you only had two, and he tells me something like, "well, my grandfather had a sex change operation" or "my father's mom was adopted, so she actually had two different mothers" or "my mom's mom was married to another woman, and my mom was fathered by an anonymous sperm donor" or "my father's family got divorced and remarried an awful lot, so I currently have 10 grandmothers". I think, well that's all theoretically possible, so I have to give him the makeup exam, but is it at all plausible? That's how we came to feel about the coincidences involved in the highly convoluted Meridiani story. Plus it doesn't explain how to form nearly identical-appearing, cross-bedded, sandy, salty, spherule-bearing rocks at Home Plate or anywhere else on Mars.

Making rare little "festoons" or trough-shaped current ripple cross-beds by the odd little eddy or vortex in a turbulent impact surge cloud seems far simpler conceptually. Such small trough shapes do occur in volcanic surge deposits - see figure and discussion in Knauth's 2007 LPSC abstract here:

http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1757.pdf

Actually, to a field geologist who habitually visualizes things in 3-D, most of the alleged Meridiani "festoons" appear to represent a topographic misinterpretation of a low-angle cross-bedded rock as viewed from above - see figure and discussion here:

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1869.pdf

Geologists sometimes call this effect "V-ing upstream". (When viewed from above, the horizontal bedding planes appear to bend up each crack and wrap around each ridge, like contour lines on a topographic map. Think of a person wearing horizontally striped pants, with you looking down at their rump from 5-feet up. The horizontal stripes will look like little troughs: UU.) The 5-foot high rover cameras can't bend down the way a real geologist could, to view the flat-lying beds from the side. Perhaps some of the 3-D image-processing gurus here at UMSF would like to take a stab at the rover "festoon" images to see if we're right or wrong about what look like troughs, but perhaps really aren't. (In other words, I'm asking for your help in discovering and visualizing the truth.)

Whatever the results of that important test, there would still be an awful lot of dead grandmothers at Meridiani, if you ask me.

BTW, the processes involved in forming impact surge deposits will probably never be as well studied or understood as those for deposition by wind and water. You can't confine a nuclear bomb to a wind tunnel, or to a tilted flume channel. If you want to observe surge deposition up close, you're dead, just like all those alleged grandmas. In the case of terrestrial impacts, fine-grained deposits begin to erode as soon as they're formed, and they're quickly gone. The extremely slow rate of wind erosion on Mars means that fine-grained impact deposits have a much better chance of being buried (and thus preserved) by later geological processes, such as more impacts. That preservation perhaps occurred at Meridiani and Home Plate, if we are correct.

--Don

[dvandorn]

There is much more data to collect before any theory is proven. I really do appreciate your efforts, Professor. And I surely understand the difficulty in direct observation of large impact events. Even if you eventually are proven wrong, we will always need people to challenge the conventional wisdom, or else misinterpretations will never get addressed!

Thanks again for joining this forum.

-the other Doug

[ElkGroveDan]

why don't you see "festoons" everywhere, across the entire area, if there was sheet flow, with no channels?)

Come on Don, now you're an educated guy. That's a bit like asking why paleontologists don't see fossils all over the Earth considering the widespread history of life here. After billions of years of who-knows-what, of impacts, wind erosion, ices, and even fluids, the region has changed. That we have to look carefully for something as small and fragile as fossilized festoons is not surprising. Their present day abundance is not necessarily indicative of historical conditions.

[dburt]

Sorry Elk Grove Dan, I didn't make myself clear. I meant: Why don't we see them continuously exposed at the same preserved level of alleged sheet water flow in areas of adequate outcrop, such as in the wall of a little crater? (Payson outcrop, I believe that area was called.) In that regard, why haven't we seen any water channels at all? Flowing water always seems to find a way to erode channels, especially in soft sand or mud, and channels are the most commonly accepted evidence for regional water flow on Mars images (together with teardrop shaped islands, perhaps). The pictures I saw of terrestrial "festoons" presented at a meeting were all in restricted areas of former waist-deep sheet water flow right next to an enormous river channel. That big river struck me as a little odd as an analog for Meridiani. I've personally seen nice "festoons" exposed only in the same environment, preserved in sandbars on the banks of the Colorado River in the Grand Canyon - again, not a possible analog for Meridiani.

For over 30 years I've taught my freshman classes that a sand-choked water flow will generally take the form of a braided stream, with dozens of little channels branching and rejoining as they make their leisurely way across a nearly flat sandy plain. Those branching and rejoining channels are the only evidence for flowing water I've ever seen on flat sandy surfaces where deposition is occurring. An example I studied on June 1 was at top of the dune-deposited Jurassic Page Sandstone, of Page, Arizona, where it was eroded down to the plane of the water table, and then washed by the water flows that deposited the Entrada Sandstone on top of it. No "festoons" at all - just dozens of little branching channels seen almost anywhere in sandstones on top of that planar erosion surface. Hike the Rim Trail that encircles the town of Page and you'll also see beautiful views over Lake Powell, and tons of hematitic concretions that don't look anything at all like the Meridiani spherules, except that they're kind of round. BTW, ephemeral braided streams are almost universal in sandy flat areas of the modern Arizona desert too, unless we're in the midst of a scouring flash flood.

So even if the "festoons" are real and not an unfortunate artifact of viewing angle, 1) something that looks just like them apparently has formed in various surge deposits too and 2) they are a highly atypical indicator of flowing water in a flat sandy environment (sort of like the 3rd dead grandmother in my little parable above). That is, possible but not plausible, and certainly not the best indicator for flowing water (highly ambiguous, as it turns out).

Note: I don't consider myself a sedimentologist. Knauth teaches that course and does that research, and I've learned something from him and from a lifetime of field work.

I hope I'm not getting too technical for most of you. I'm really trying to avoid that. Oh well, vote with your eyes, I guess, but please let me know.

--Don

[ElkGroveDan]

I hope I'm not getting too technical for most of you.

Don't know about anyone else but I'm jogging along right next to you Don. I may be rusty on my physics and calculus, and TD is just a painful memory but I've kept my background in geology and geophysics well-polished.

[marsbug]

I'm no geologist or chemist but the impact surge argument seems very straight foward and logical, possibly more so than any other hypothesis I've heard. I understand that the chemistry of home plate is very suggestive of the presence of water. Could the chemistry of home plate be accounted for by the impact surge hypothesis alone, or would the occasional presence of water still be required?

[dvandorn]

My wonderment with the impact surge theory is how it resulted in the finely layered rocks we've been calling evaporite. That would require, through the 800 meters estimated thickness of the unit, tens of thousands (if not more) separate impact surges, would it not? Each one depositing a millimeter-thick layer with only occasional cross-bedding? And the variations in chlorine and bromine -- those are excellently explained by hydrodynamics. How does impact surge theory explain them?

I see tens of thousands of dead grandmothers lurking here...

-the other Doug

[centsworth_II]

...the 800 meters estimated thickness of the unit...

The mind boggles. Opportunity is looking at the tiniest fraction of the
overall history of Meridiani. I don't think the base surge explanation
for the festooned layers that Opportunity has seen denies that the overall
800 meter deep stack of evaporites could have been laid down in the bed
of an ancient sea. The base surge theory only says that an impact would
rearrange that material into the small scale features seen by Opportunity,
in the limited range of layers that she is looking at.

It's the festoons -- the small smiley-faced ones that it's said could be
formed in a matter of hours, or minutes -- that concern me. I think
it's legitimate to ask what caused the water flow that would be
necessary to form them. What rate of flow is necessary?

The way I see it, the berries could very well be concretions formed in water
long after the festoons formed, by whatever means. In this case,
the berries do not need to be explained by the base surge theory.

[dvandorn]

Oh, believe me, I'm grateful for the Professor in bringing up the impact surge theory. Impacts have shaped the surface of Mars moreso than they have of Earth, and any geological analysis that doesn't take that into account is ignoring a bunch of 800-lb gorillas in the room, so to speak.

As for the lack of braided channels in the layers we can see -- that bothers me, too. Always has. I wonder a bit about the movement of water in a lower-gravity environment, and whether or not this could have an effect on channeling in shallow water. But when I look at various images of Meridiani, I do see evidence of mud-cracking-type features (such as Anatolia).

Taking everything altogether, Occam's Razor points at water, to me. But I seriously appreciate the concept of alteration by impact processes, since such processes *must* have been occurring throughout the formation of these units.

-the other Doug

[Floyd]

In general I think we are talking about standing water, not flowing streams. Is the atmosphere of Mars strong enough to ripple the surface of a lake such that festoons form on a sandy bottom?