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

[centsworth_II]

...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.

This does not have to be either/or: Water or base surge.

Water for the original evaporites. Water for the vugs, concretions,
and "mud cracks". I can see all that. But I'd like to see more on
how the small, smiling festoons were caused by surface water.

[stevesliva]

My wonderment with the impact surge theory is how it resulted in the finely layered rocks we've been calling evaporite.

I wonder if the atmospheric conditions over quite a larger area would gain higher levels of vapor, condensation, precipitation after an impact... given the explanation for frost at the Viking sites involving CO2 precipitation, I won't hazard to guess what materials CO2, H2O, liquid-hot magma, etc are involved. But fine-layering, I'm sure there's some way that's compatible with overlapping clouds of vapor created by various impacts.

[dburt]

Nice to hear that my remarks of last night have generated some more discussion. I have to sleep, hug my wife, and do my day job too sometime, so sorry I can't chime in more often. Glad also to discover that I haven't been too technical yet, and that all are following the "dead grandmothers" argument without being a professor or teacher (of course, among us it's a standing joke that grandparents seem to die only on test days).

With regard to some of the preceding comments, at Meridiani and Home Plate the amazing rovers are imaging only the same surface rocks that can be imaged from orbit, but in infinitely more detail and from many more angles, along with multiple instruments that yield compositional and mineralogical-petrological information. The brush and RAT, plus unintended wheel dragging, have been exceedingly helpful too. Still, what lies beneath either site can only be guessed at, except where impacts have excavated samples of deeper rocks.

Impact cratering at Victoria Crater has excavated only the same sandy, salty, cross-bedded, spherule-rich rocks seen earlier in Endurance and Eagle craters - no signs whatever of standing water (i.e., no shales or lake beds). Driving into the crater may reveal more (e.g., a detailed record of layering, called stratigraphy by geologists), but it is unlikely to reveal any new rock types. Orbital imaging suggests deeper rocks (nearly a kilometer thick, and therefore potentially much older than those at the surface) are also finely layered, and, most intriguingly, Ken Edgett's 2005 article in the Mars Journal suggests that some of these deeper rocks may contain flow channels of some sort. It would be highly premature to state what geological processes (water, wind, volcanism, impact) might have formed these older, deeper beds without looking at them up close, however. We have never claimed that they are all impact deposits - we have just stated that some or all of them could be, because Edgett also noted that they appear to be interstratified with numerous impact craters, indicating that lots of cratering was going on as they were deposited. Keep in mind that impact deposits can be channeled like any other rock - the channels don't indicate water deposition, only erosion. Also, processes other than water flow can erode channels too, as Nick Hoffman has emphasized in his "White Mars" interpretations of outflow channels and young gullies. There are plenty of gaseous mixtures that, in bulk, have much in common with a watery fluid. (Steamy, high-velocity surge clouds making various types of cross-beds, for example.)

Impact cratering inside (or in the region of) Gusev Crater does not appear to have excavated any of the expected lake beds either - just variably vesicular lavas (some or all of which might instead be impact melt - on the surface we see only the broken pieces, not the lava flows) and possible small pieces of layered surge beds. On the other hand, no particularly deep craters have or will be (given its dragging wheel) visited by Spirit. If there were a small explosive volcano nearby, it could have excavated rocks going all the way down to its source region (region of rock melting - very deep indeed). Unfortunately, no volcanic constructs or explosive craters are visible nearby, despite possible volcanic indicators in the cross-bedded surge rocks of Home Plate, which are more likely simply more impact surge (I've made no secret about that being our present interpretation).

The above stratigraphic review is just to demonstrate that we haven't made any of the possibly outlandish claims about impact deposits that some people seem to have attributed to us. Our working hypotheses are strictly based on the daily images and published data that has been released to date, and mainly concern the youngest rocks (those exposed at the surface and imaged by the rovers).

[David]

no particularly deep craters have or will be (given its dragging wheel) visited by Spirit

Except for that insignificant little depression called "Gusev"...

[Guest_AlexBlackwell_*]

Nice to hear that my remarks of last night have generated some more discussion. I have to sleep, hug my wife, and do my day job too sometime, so sorry I can't chime in more often.

You have to learn to put UMSF at the head of the above-listed queue. Of course, then you'd have to add "see a divorce lawyer and go to the unemployment agency" at the end

[dburt]

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?

Superb question! Really sets me off (the flattery doesn't hurt either ). In principle, what impacts do is vaporize, excavate, and scatter what was already in the target volume, as modified by vapor condensation and generally minor chemical input from the impactor (a comet or meteorite). Turbulent surges also scour the surface across which they flow, possibly modifying the cloud chemistry. Impact doesn't create anything new, except high pressure minerals and impact melt (and vapor and condensates, including spherules) - it's main effect is to homogenize and scatter what was already there.

Most salts at Meridiani (except jarosite which, following Roger Burns, we attribute to iron sulfide weathering - impact acid steam condensation has alternatively been suggested by a colleague, Misha Zolotov) probably formed in liquid water (brine) long before impact may have scattered across Meridiani. If early Mars worked like early Earth, the salts mainly date back to shortly after the planet formed, when acid steam, released by planet-wide degassing, condensed into the first warm seas. The acids rapidly reacted with basic rocks like basalt to form neutral salts containing Mg, Ca, and Na.

To concentrate the dissolved salts into a dense brine or crystals, we like freezing more than evaporation. That is, given the choice between hot vs. cold for early Mars, we choose cold, because Mars has always been much farther from the Sun and much smaller than Earth. As the seas froze down and the ice sublimated, the brines beneath got more and more concentrated (denser), and gradually sank into the subsurface, where they were trapped beneath ice or permafrost.

Whether cold or hot (relatively), early Mars was certainly bashed by impacts, probably most of them just before 3.8 billion years ago (the so-called late heavy bombardment). These impacts obliterated the early surface history of Mars and scattered salts and, we hypothesize, sulfides across the surface. Afterwards, the surface of Mars was about as it is today, extremely cold and dry, with an atmosphere close to a vacuum, so that liquid water (and even ice in most places) was unstable or extremely ephemeral. Large amounts of water apparently survived in the subsurface, however, as both ice and (probably) deep brine (as evidenced by occasional catastrophic releases to outflow channels that possibly formed ephemeral seas in the northern lowlands).

We tentatively date the Meridiani surface rocks (= youngest geologically) to the tail end of the late heavy bombardment period, when the surface of Mars already could not support liquid water as streams or lakes (given that there is no geological evidence of any at Meridiani - in this our interpretation differs completely from that of the MER team). The surface climate matters very little for the impact process itself, but does affect the preservation potential (cold and dry = very slow wind erosion only, allowing weak Meridiani sediments, cemented only by soluble salts, to survive until the next distant impact buried and preserved them). So to answer your question (you say, at last!), no liquid water is indicated by the salts, other than minor quantities resulting from condensation of steam in the original surge cloud, or whatever the salts themselves could attract from the atmosphere (i.e., water in surface brine films and occasional drips). This minor water was enough to rust sulfides and dissolve (leach) the most soluble salt (probably a chloride), leaving hollow crystal cavities, but was not enough to crystallize clays, destroy jarosite, recrystallize the soluble salts in bulk (reducing rock permeability to zero), or form the extremely coarse (giant in places) salt crystals that characterize actual evaporites or other water-soaked salt deposits. Our impact surge hypothesis resembles the extremely complex one of the MER team only in that we agree that the salts must have been transported from somewhere else (a realization they apparently came to only after we had pointed out to them, in our initial "brine splat" presentations of 2004, conceptual problems with having the most soluble and least soluble salts intimately mixed together in an alleged evaporite). That "somewhere else" could be any large salt concentration in the subsurface for us, or a hypothetical giant vanished playa lake (for which there is absolutely no surface or shallow subsurface evidence at or near Meridiani) for them. Our hypothesis can be generalized to any sandy, salty, layered sequence on Mars (including Home Plate in Gusev Crater), theirs cannot. Our allows for the actual appearance and extremely broad distribution of "blueberries" as impact-derived spherules (with similar-appearing ones occurring at Home Plate and probably many other places); theirs does not. And so on and so on, but I hope you are getting the general idea. I emphasize that the above impact story is merely a working hypothesis that undoubtedly is wrong in some details, but in its present form it appears consistent with all available evidence (I trust everyone will feel free to disagree vociferously).

Wow, ask a simple question and get a simplified geological history of Mars! What a deal! Oh well, you know me by now. As Arne said in T2, "Of course, I'm a terminator", I say "Of course, I'm a herr doktor professor" (who kills grandmothers by his tests, and every else by his long lectures...).

[nprev]

...you're killing me, Professor; none of my profs ever had a sense of humor like this...

One quick question re the 'ancient salts' hypothesis: What about the atmospheric effects of comparatively recent vulcanism such as the Tharsis Uplift? (IIRC, that's thought to have happened 100-200 MY BPE). It seems reasonable to assume that most of the outgassing was CO2 and water accompanied by a rise in atmospheric pressure (how much & for how long, no idea...though the Big Four are, like, big, so thinking that this had to go on for some time).

Anyhow, what I'm wondering is how apparently water-soluable salts could have survived near the surface during this epoch; certainly atmospheric water vapor should have penetrated the surface below the first few inches of the soil. This makes me think that these deposits were produced later in Martian history after vulcanism subsided and the atmosphere devolved into its present state.

[Guest_AlexBlackwell_*]

...you're killing me, Professor; none of my profs ever had a sense of humor like this...

Yes, laughing at the professor's jokes is one way of improving your grade

[nprev]

Oh, yeah...but I don't have to force it here!

[centsworth_II]

Our hypothesis can be generalized to any sandy, salty, layered sequence on Mars...
theirs cannot. Our [hypothesis] allows for the actual appearance and extremely broad
distribution of "blueberries" as impact-derived spherules...theirs does not. And so on...

So when is some geological society going to host a conference where proponents
of these theories can face off. It would be good to get more geologists with varied
expertise and experience weighing in.

[Bill Harris]

...no liquid water is indicated by the salts, other than minor quantities resulting from condensation of steam in the original surge cloud, or whatever the salts themselves could attract from the atmosphere (i.e., water in surface brine films and occasional drips). This minor water was enough to rust sulfides and dissolve (leach) the most soluble salt (probably a chloride), leaving hollow crystal cavities, but was not enough to crystallize clays, destroy jarosite, recrystallize the soluble salts in bulk (reducing rock permeability to zero), or form the extremely coarse (giant in places) salt crystals that characterize actual evaporites or other water-soaked salt deposits.

You are wrong.

--Bill

[centsworth_II]

...no liquid water is indicated by the salts, other than minor quantities...

And besides the large amounts of liquid water involved in the original
formation of the salts, right?

If early Mars worked like early Earth, the salts mainly date back to shortly
after the planet formed, when acid steam, released by planet-wide degassing,
condensed into the first warm seas. The acids rapidly reacted with basic rocks
like basalt to form neutral salts containing Mg, Ca, and Na.

[dburt]

This does not have to be either/or: Water or base surge.

Water for the original evaporites. Water for the vugs, concretions,
and "mud cracks". I can see all that. But I'd like to see more on
how the small, smiling festoons were caused by surface water.

A "mud crack" is formed in mud, by definition. No layer of mud (called shale when hardened into a rock) has yet been imaged anywhere at Meridiani, so far as I know. Therefore, no mud cracks. (This term has not, so far as I'm aware, been used by the MER team.) The polygonal cracks that affect the layered rocks have been called "bulk shrinkage cracks" and can occur in various types of rocks - what environment they indicate is therefore ambiguous. They could indicate drying (shrinking) of clays (as in mud), dehydration of salts, a response to temperature decrease (like columnar jointing in lavas - vertically oriented bulk shrinkage cracks whose orientation is controlled by the flat geometry of the flow as it cools and shrinks), or some other process.

FWIW, polygonal bulk shrinkage cracks are common in sandy, cross-bedded surge deposits (which of course is what we believe Meridiani consists of). Such shrinkage presumably occurs as the rocks cool and they lose the steam that permeated the them during deposition. See Knauth's 4th figure here:

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

We were together when he took that photo; I've seen similar shrinkage cracks in other surge deposits.

As per salts implying water, see my above "terminator" post (not if the salts were formed earlier and then transported to Meridiani, which is one interpretation we agree with the MER team on).

As per the alleged "festoons", see my post of a day or two ago - "festoons" need not indicate flowing water, because they apparently can form in surge deposits too (a different type of flow), and most at Meridiani may simply be an artifact of viewing angle (which I'm still hoping someone here can confirm or prove wrong). "Festoons" are a cross section through "current ripple marks" (tiny moving sand dunes, conceptually) and form in a manner distinct from "oscillation ripple marks" which form in very shallow water due to the influence of surface waves on the water.

Only minor water, such as liquid condensed from the steamy surge cloud or water attracted from the air by the salts itself, is needed to leave the Meridiani crystal cavities (again, see my "terminator" post). (BTW, the technical adjective for salts that attract water - most do - is hygroscopic or, in extreme cases such that a salt attracts so much water that it liquifies in place - self dissolves, as it were - is deliquescencent.) Calcium chloride, probably a common salt inside Mars, is deliquescent, and it is commonly used in laboratories as a drying agent because it sucks so much moisture out of the air.

And of course, the only water needed to form what the MER team calls "concretions" is condensing steam (or another vapor) in a surge cloud, if they are impact-related spherules (as their perfectly spherical shape, uniformly tiny size, Ni-enrichment, blue-gray color, and pattern of distribution suggests).

Please prove me wrong.

--Don

[dburt]

And besides the large amounts of liquid water involved in the original
formation of the salts, right?

You got it. Lots of water somewhere, somewhen, but not at Meridiani then (or since).

--Don

[centsworth_II]

Lots of water somewhere, somewhen, but not at Meridiani then (or since).

Why assume that the salts did not form at Meridiani billions of years ago.
Is it only because they had to form somewhere else in order to be moved
to Meridiani by base surge?