[X] My Assistant

[dburt]

Relevant to Emily's boulder observation, the "Gullies and layers" HiRISE image was not the first to show layers with abundant boulders, indicating poor sediment sorting in layered slopes. Previous images included, e.g., PSP_001691_1320 "Gullied trough in Noachis Terra, released on 28 Feb., and PSP_001942_2310 "Signs of fluids and ice in Acidalia Planitia" released on 9 May. That these bouldery layers might represent ancient ballistic impact ejecta seems a reasonable suggestion, because much of the present martian surface is littered with boulders presumed to be ballistic impact ejecta. Other possibilities for boulder deposits might include, e.g., ancient talus or landslide deposits at the foot of slopes, stream boulders in channels, volcanic ejecta near vents, glacial moraines, or iceberg dropstones.

As an aside, the related suggestion that at least some of the fine-grained layers above or below any boulder deposits (or elsewhere on Mars) could likewise represent ancient impact deposits (non-ballistic fine-grained sand and dust distributed over vast areas by fast-moving, turbulent, erosive gaseous density currents - a.k.a. impact surge clouds - or by the winds as later fallout) already seems to have aroused considerable controversy on this forum, but again that's peripheral to Emily's boulder comment.

--Don

[MOD EDIT: "Brine Splat Burt" discussion moved here -> http://www.unmannedspaceflight.com/index.p...ic=4308&hl= -EGD]

[centsworth_II]

As an aside, the related suggestion that at least some of the fine-grained layers above or below any boulder
deposits (or elsewhere on Mars) could likewise represent ancient impact deposits (non-ballistic fine-grained
sand and dust distributed over vast areas by fast-moving, turbulent, erosive gaseous density currents - a.k.a.
impact surge clouds - or by the winds as later fallout) already seems to have aroused considerable controversy
on this forum, but again that's peripheral to Emily's boulder comment.

So you're the dburt of Basal Surge fame?

"ASU geologists L. Paul Knauth and Donald Burt, who along with Kenneth Wohletz of Los Alamos National
Laboratory, say that base surges resulting from massive explosions caused by meteorite strikes offer a simpler
and more consistent explanation for the rock formations and sediment layers found at the Opportunity site."
http://www.asu.edu/news/stories/200512/200..._meteorites.htm

I haven't followed the situation closely enough to ask any good questions, but I wonder if anyone else here
would like to ask about your current views.

for reference, the basal surge thread is here:
http://www.unmannedspaceflight.com/index.p...surge&st=30

[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.

[dburt]

...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.

Owing to plate tectonics, Earth probably has at least as much volcanism today as Mars ever did, plus coal-burning power plants and smelters are continously tossing a sulfuric acid precusor (SO2) into the air. This has minor effects (such as slight climate cooling - which we badly need in Phoenix) but the ground hardly is littered with jarosite, gypsum or other relatively insoluble sulfates. Consider early degassing of an entire molten planet, compared with the little bit of steam and CO2 and SO2 that comes out of a lava flow or even volcanic steam explosion - a drop in the bucket, literally. As I understand it (not my field), the atmospheric pressure on Mars is close to "buffered" by CO2 ice at the poles and in fact Mars has been continuously losing atmosphere very slowly since the end of the late heavy bombardment. Evidence for climate change is mainly blamed on obliquity and orbital variations (how much Mars tilts on its axis and how non-circular its orbit is). Some people try very hard to make Mars temporarily warm and wet with volcanism, which may be possible, given how little atmosphere there is to begin with, but I imagine that this effect could be dwarfed ty the effect of a large impact (especially during the boom boom boom of the late heavy bombardment). Impact was adequate both to warm Mars up (very temporarily) and deposit thick layers of salty sediments. As should be obvious from my abbreviated history, I'm with the very wet, but very cold and salty school of early Martian geology (at least until more information becomes available). Show me the palm trees, I say, before I bring my swimming suit.

The fact that water soluble salts have survived near the surface is just what makes me think that it hasn't rained on those parts of Mars in 3.8 billion years - or at least, not much. (Snow or frost is okay for survival of sulfates - see below.) In Arizona, after a small rainstorm (something else we badly need), the sulfates on mine dumps sink into the ground owing to dissolution and then, over the next several weeks, they reappear as colorful crusts referred to efflorescences (because they can look like flowers blooming). I think that's what we're seeing in the cauliflower-like crusts of salts being imaged just below the surface at and near Home Plate. The low pressure makes the salts effloresce just beneath, rather than above, the surface. The driving force is simple capillarity and evaporation of moisture - dip a paper towel into salty water, the water rises up (wicks up) by capillarity, and then evaporates, leaving salts behind - far above the surface of the water. And many salts generate their own brine from atmospheric moisture, so that capillarity can make deep salts wick upwards towards the surface, without rain. This effect was much discussed with regard to formation of "sulfate duricrust" during Viking days, but seems to have been largely neglected in recent discussions.

My general attitude (Occam's razor) is I don't want to invoke any unusual effect or phenomenon, especially anything I can't see direct evidence of, until I am forced to by the data. That's how I feel about "warm, wet" early Mars - it seems to me that impact alone, for which there's abundant evidence at every scale, may suffice for a lot of what people want to blame volcanism, or greenhouse gases, or whatever on. Occam was apparently a medieval theologian (and logician) who got upset when people wanted to blame every event or phenomenon on mysterious, invisible angels. I feel the same way about invisible geological features (missing playas and missing volcanoes) on Mars.

BTW, if you want surface water under present martian surface conditions, just dissolve lots of salts in it (mainly chlorides, not sulfates - the sulfates litter the surface, and the chlorides don't, because the sulfates have very little abilty to depress the freezing point of ice). If frost lands on mixed salts, the chlorides are leached, and the sulfates are not. Knauth and I published papers on that in 2002 and 2003, as mentioned in a previous post, I think, and blamed the crystal cavities at Meridiani on the same phenomenon in our 2005 Nature paper.

Playing the professor again, I'm afraid. All out of jokes, though.

--Don

[dvandorn]

...missing volcanoes ...on Mars.

Ummm... if the Tharsis shield volcanoes and dozens of other classic calderas readily observed on Mars aren't volcanoes, and if the very clear and obvious lava flows (which read as basalt from both surface and orbital spectral analysis) aren't volcanic, then what are they?

I hate to say this, but if your theories are based even a little tiny bit on this "observation" that Mars is "missing volcanoes," then you do seem to be ignoring empirical data (labeling it "theoretical") that doesn't fit with your own theories, and that's when the scientific method fails.

I'm sorry -- I simply *must* have misinterpreted what you mean, here, since that statement is so obviously false.

-the other Doug