Apologies if this story has already been picked up and reported by someone, and I missed it, but I don't recall reading anything about it here...

HiRISE spots possible evidence for thermal springs on Mars

I checked out the HiRISE pic in question ( PSP_002812_1855 ) and here's a couple of crops of the area in question...

Click to view attachment

Click to view attachment

Interesting stuff... that's gotta move Vernal Crater up the list of possible landing sites for future hardware..?

A little bit more info can be found in this Q&A...

we need a mineralogical signature to corroborate the hot spring idea........silica!!??

Thanks, Stu; been waiting for this! Now we just need to find one little teeny one that's still steaming...

Yeah, that would be something wouldn't it?

I think this is quite a big story... a hot spring would be a great place to look for signs of past life after all... pretty amazed there hasn't been more discussion about it here...

Springs can deposits all sorts of minerals, depending on water chemistry and temperature. Common ones include sulphides (pyrite, marcasite) , oxides (haematite, pyrolusite), hydroxides (goethite), silica (quartz, opal), silicates (clays), and sulphates (anhydrite, gypsum, jarosite, alunite). The terrestrial analogues mentioned, Dalhousie Springs, deposit mostly carbonates (with minor pyrolusite, clay, gypsum, and geothite). But the geomorphic relationships and scale of features seen at Dalhousie would be applicable to a wide range of other mineralogies. I think they are excellent analogues for what eroded martian springs might look like and all scales.

Jon

More to read:

ANCIENT HYDROTHERMAL SPRINGS:

"The areal density of 5-25 m-diameter craters on each martian mound is approximately 150 per km², suggesting that the two features are roughly contemporaneous, with maximum surface ages of approximately 100 my"
"The composition of the Vernal features is uncertain. Unique mineralogy of the mounds was not detected by CRISM. Spectra from Vernal Crater are dominated by the bright dust that is ubiquitous in Arabia Terra.Nevertheless, the light tone of the mounds is clearly in contract to surrounding sediments and this suggests that the mounds are composed of a distinctive mineralogy. The persistence of the topography and terracing of the Vernal mounds, despite ubiquitous wind erosion, suggests that these features are indurated, analogous to the cementation observed in terrestrial spring deposits."

CANDIDATE LANDING SITE FOR THE MARS SCIENCE LABORATORY: VERNAL CRATER,:

"There is an interesting section of the crater located in the south which is thermally bright in both day and night THEMIS infrared images. (it shows up dark in Figure 1 because it is an inverted daytime IR mosaic of msl_24-dayir.jpg [5])."

I shouldn't wonder if mounds related to the thermal anomaly. Can anyone locate mounds within IR mosaic?
If this is the case, we have first evidence of the contemporary hydrothermal activity on Mars.

This would be an interesting possibility. Of course the mound morphology, at least at Dalhousie, only emerges after the springs and shown down. The indurated resists erosion as the surrounding landscape is lowered. Also, although the Dalhousie springs are warm (presently up to 47 degrees), other mound springs are at ambient temperature, so they need not be associated with a positive day time thermal anomaly.

Vernal crater is supposedly Hesperian, so any thermal anomaly associated with the impact is long gone. if warm waters are at or near the surface, or have done so since the hesperian, then may be an indicator of regional groundwater flow, as at Dalhousie.

Jon

Here it is!
I combined IR mosaic with HiRISE image - mounds located exactly in the thermal anomaly. So actually we have a kind of hydrothermal activity here.
Another interesting point - a lot of small circular black features can be seen in the area of anomaly (see Stu's original crops). That's a pits, I suppose, and I'll bet my hat that pits are main contributors to the anomaly IR emission.

Doesn't the dark color actually mean it is colder there? Or are the colors inverted?

If its the same image as the one in the paper linked by IM4 then yes the colours are inverted (and it does look similar).

That's jumping to a conclusion more than just a bit:

From the Washington Post article "spectrometers on the orbiter have not found evidence at the site of the kind of minerals that would be expected around a hot springs."

Carefull about imposing your wishes onto a partial data set without looking at the whole picture.

The last statement in the WP article (webchat transcript, really) by Mr. Kaufman was VERY interesting:

"I'm told the area has been dry for tens of millions of years. Sounds like a long time, but that is actually considered quite recent in planetary terms."

I only hope that it was accurate.

There's a detailed presentation on Vernal Crater (50MB) from the Second MSL Landing Site Workshop (Oct 2007).

Go to: http://marsoweb.nas.nasa.gov/landingsites/...op/program.html

From there, scroll down about halfway down the page to where it says "SW Arabia Crater" (that's Vernal), by Carlton Allen. Presentation can be downloaded there.

LINK FIXED

Recent article in space.com about fossil preservation with acidic minerals: http://www.space.com/scienceastronomy/0805...-life-iron.html

It references a recent article in Icarus: Fernandez-Remolar Icarus 194 (2008) 72-85. "Fossilization potential of iron-bearing minerals in acidic environments of Rio Tinto, Spain: Implications for Mars exploration". doi: 10.1016/j.icarus.2007.10.009

(Pay-for article. Abstract available here.)

Rio Tinto in Spain is considered a possible Earth analog for Meridani Planum. It also might be valid for other locations where groundwaters percolated through iron sulfide ores that were themselves emplaced by hydrothermal activity. The authors state that "Fossil preservatoin by iron oxides in the acidic environment of Rio Titno suggests that if life was present when sedimentary rocks formed at Meridani Planum, Mars [or in similar locations as well], precipitated minerals could record their presence."

At the very least, the images and descriptions of Rio Tinto in the space.com and Icarus article can give a concrete example of what Meridani Planum and the thermal spring environment might have looked like (minus the oak leaves, of course).

-Mike

We should not assume that mound spring deposits on Mars would be dominated by primary acidic minerals. In fact if they are formed by regional groundwater discharge is unlikely that they would be.

Jon

Yup!

Here is a freely accessible abstract (thanks, JonClarke!) that describes Dalhousie Springs as a potential Earth analog of a martian mound spring deposit:
Clarke and Stoker LPS 34 (2003) Abstract 1504. "Mound spring complexes in Central Australia: an analog for martian groundwater." Abstract freely available here.

Another abstract (again, freely accessible), provides a great overview of the formation of the Dalhousie Springs complex:
Bourke et al. (JonClarke listed as co-author as well) LPS 38 (2007) Abstract 2174. "Spring Mounds and Channels at Dalhousie, Central Australia." Abstract freely available here.

Getting back to the basic discussion (sorry, couldn't resist ) of the pH:
From the first abstract, the Dalhousie Springs water pH is about 6.8-7.3 (which is pretty neutral. human physiological pH is 7.2-7.4)
In stark contrast, Rio Tinto has a pH of 1.5-3 (very acidic. acetic acid (vinegar) is about 4.5).

Two different analogs of (different) martian environments with two different pH's.

-Mike

Agree with Jon about the improbability of acid martian groundwater, unless biological (or other) processes are constantly adding large amounts of acid to the groundwater (e.g., at Rio Tinto through the active biological oxidation of a huge massive sulfide deposit), overwhelming its ability to react with its wallrock.

-- HDP Don

I poked around on the web and got myself thoroughly confused. Someone please help explain why the groundwater would be necessarily neutral.

One source I found says that Mars regolith is neutral (pH 7.2) at the Viking Landing Site (which?) according to a model based on results from the Viking Labelled Release data : http://articles.adsabs.harvard.edu/cgi-bin...p;data_type=PDF

Yet another source says that Mars pH is not known: http://quest.arc.nasa.gov/mars/ask/soil/pH_of_Mars.txt

One source proposes the “dry” oxidation of Fe(2+) to (Fe3+) via percarbonate radical [CO3(-1)]] in a heterogeneous medium: http://www.marslab.dk/ResearchSurfaceChemistry.htm

(the nitrate anion was used as a “joe high oxidation state species” in this sequence)
NO3(-1) {nitrate anion,} + UV--> ONOO(-1) (peroxynitrite radical)
ONOO(-1) +CO2-->[ONOO, CO2](-1) (peroxynitrite ion/carbon dioxide adduct)
[ONOO, CO2](-1)-->NO2 + CO3(-1) {carbonate radical}
CO3(-1) + Fe(2+)--> Fe(3+) + CO3(-2)
The overall proposed process would have the effect of bringing CO2 from the atmosphere into the rock in the form of carbonate (carbonates are basic) in a medium that would prevent efficient ion transport (neutralization). [Alka-Seltzer doesn’t fizz ‘till you put it in water.]

On the other side of the aqueous pH scale, the Meridani hypotheses put forward indicate that acidic minerals emplaced there would have made that region’s groundwaters acidic.



If there was poor ionic exchange between rock of one type (acidic) and rock of another type (basic), then the groundwater could be at any pH (acid or base), depending on which rock predominates the particular aquifer, correct?

And if I understood my surfing correctly, the pH of martian soil has never been directly measured.

Help?

-Mike

Some future relief for you, Mike. According to this excellent article on spacEurope by project astrobiologist Lewis Dartnell just published today, Phoenix will indeed perform direct pH measurements, and apparently at four levels of depth!

Nick...Lewis isn't project astrobiologist...is OUR resident astrobiologist...
Seen those pretty (and expensive...) t-shirts?

I stand corrected, Rui...and those are AWESOME T-shirts!!! Sorry you had to pay out the yang to get 'em for the contest!

Soil pH and and potassium, too! Excellent! Now all we'll need is available soil nitrogen and phosphate and we'll know what kind of fertilizer to add in come planting time!

Mike - pH is measured in liquid water. The pH of a soil is measured by moistening it, if it is dry. A jarosite-bearing Meridiani soil (or a Gusev soil that likewise contained acid sulfates) would presumably yield an acid pH, if it were moistened. "Acid sulfates" yield acid if dissolved in water.

Groundwater is presumed to have reacted with buried rocks and bedrock, at leisure and over great time, and its pH generally reflects that reaction. On impact-dominated Mars, almost all of the rock pieces seen to date by the two rovers have been basalt (except for some even more basic types, and some metallic meteorites, and an unusual layer of fragments rich in silica near Home Plate). A basaltic rock (or virtually any other common rock type) reacting with any water (acidic or basic) should eventually yield a neutral to basic solution. That is why virtually all groundwater on Earth has a neutral to basic pH, unless it is sitting on top of an igneous system that is actively boiling off acidic gases such as sulfur dioxide (e.g., is sitting on top of an active volcano, as in a crater lake or geyser basin), or is draining an actively oxidizing sulfidic mine or mine dump (AMD = acid mine drainage). Otherwise, the amount of rock is very much greater than the amount of groundwater, so the latter must eventually be neutralized. Think of it as a slow titration of possibly initially acid water against basic rock, with the basic rock always in huge excess. Pulverization of the basic rock, as by impacts on Mars, should speed up the reaction.

I hope this explanation helps.

-- HDP Don

As usual, Prof Don, it does indeed help.
Wherever your thinking may lead you, you don't hold back on your learning.

Many of us profit as a result.
Thanx,

Thanks! That helped muchly!

I guess the more basic question (sorry again!) is why martian basalts are necessarily of high pH? (more basic)

Please correct me if I'm wrong, but I'm assuming it is the metal oxides [CaO, MgO, and Na2O, Fe, Al and their buddies] in basalt, that on dissolution/exposure to water form metal hydroxides and suck up protons from the (minimally buffered) aqueous solution. By definition: lower proton concentration = lower pH.


A fairly recent abstract [Hurowitz et al. LPSC (2005) Abstract 2025. Experimental basalt alteration at low pH: implication for weathering relationships on Mars.) mentions that the weathering relationships on Mars under low pH (high acid) conditions cause a different set of alterations. According to the abstract. At "neutral pH" (pH 5-8) alkali metals (Na, K, Ca, Mg) are leached out and leave behind Fe(III) and Al. At acid pH (pH 1-4), oxidation to Fe(III) is inhibited and Al is much more soluble than at neutral pH.

[Al(OH)3 is amophoteric - it dissolves better in basic or acid media than in neutral media due to the formation of different species at either acid or basic pH. In the chemical laboratory, aquous aluminum salt workups can make some nasty emulsions. (Hint: acidify your AlCl3 workups with with phosphoric acid)]

[More trivia: iron salts are less available to plants at neutral or basic pH. Certain plants that lack efficient siderophores (iron-chelating enzymes responsible for fetching this nutrient to cells), like blueberries, need a more acid soil to be able to thrive. This is why most blueberry plants do better at soil pH's in the range 4.5 - 4.8.]


The rock weathering pattern is pH dependent. Earth rock weathering patterns are generally consistent with neutral pH weathering. According to the abstract, the Mars surface rocks seem consistent with low pH surface weathering. By comparing the interior of Adirondack (and Humphery, too) rock at Gusev with it's (weathered) exterior, it appears as if olivine has been "dissolved" away from the outer layer of Adirondack.

Their concluding sentence: "Martian rocks and
soils do not mimic the weathering trends produced by
basalt alteration on Earth, indicating they have not
been altered by interaction with large volumes of moderate
pH rainfall or groundwater."

So it appears that any surface and near surface waters (if they were present) and the groundwater traveled in different circles.

Don't use well water for your martian blueberry farm .

-Mike

Mike - This started out as a discussion of groundwater locally exiting from springs and you have now brought up weathing and acids falling from the sky. They are not the same, as you realize, because the ratio of water to rock can be much larger for weathering-type systems, especially if they involve torrential downpours, and because weathering alteration conceptually occurs at a single planar rock-water interface (the ground or rock surface) rather than throughout a 3-D network of connected pore space being slowly traversed by relatively small quanitities of groundwater. Focusing water flow at a surface (or along surfaces on either side of a hydrothermal vein) leads to effectively higher water to rock ratios, at least at the site of reaction.

So-called Mars-analog experiments on acid weathering of basalt are generally carried out with relatively huge amounts of fluid and very little basalt - otherwise the acid wouldn't stand a chance. That is because, as you guessed, basic igneous rocks like basalt are rich in basic oxides such as MgO, CaO, and Na2O and poor in insoluble silica (SiO2) and alumina (Al2O3), which oxides have relatively little effect on the pH of dilute waters. As a general rule, the more silica-poor the lava, the more likely it is to neutralize acids rapidly. Basalt, especially olivine-rich basalt, is silica-poor.

You can decide if torrential acid rains ever characterized Mars. I think they could have, but only ephemerally, owing to acid vapor condensation right after really major meteorite impacts, during the early and middle late heavy bombardment (LHB). Roger Burns-style weathering of pulverized sulfides is another possibility and is certainly not mutually exclusive. For a variety of reasons, I don't think there was ever a long-term Martian atmosphere that was dominantly sulfur dioxide and water vapor in place of carbon dioxide, as implied by the warm, wet acid-weathering model. In any case, everyone agrees that afterwards, everything suddenly turned frosty and dry, or the acid sulfates and soluble sulfates wouldn't still be preserved at the surface. When I look at Mars I still see (somewhat to my surprise) mainly the physical and chemical after-effects expected of ancient impacts.

I used to pick lots of blueberries before moving to Arizona. The acids involved in conventional blueberry swamps are mainly organic, I believe (I recall stepping on lots of moss and dead leaves). So well water might be fine for growing blueberries on either planet, so long as lots of dead plant material (humus) was around as an acidic substrate for the berry bushes.

-- HDP Don

Thanks!

I think I understand:
A "typical" spring on Mars should thus be basic to neutral due to the massive buffering effect of basic basalts on the circulating groundwaters.

A "weird" spring on Mars could be acidic if there were some atypical conditions:

• localized depletion of buffering ions (atypical emplacement of high silica rock)
• groundwaters circulating and held incommunicado in a large (isolated) collection of acidic dust (e.g. ancient, deeply buried acidic dust-filled crater)
• groundwaters circulating near a (sulfate rich [acidic]) hydrothermal vein
• groundwaters resulting from collection of surface runoff interacting with surface acidic dust that is somehow isolated from interaction with deeper rock (not real likely, but I thought I'd mention it).

The recurring theme for acidic springs would be some type of isolation from martian-typical basic basalts.

So, it's most likely that the feature most recently imaged is a neutral/basic spring with neutral/basic deposits.


On a slightly different topic, would that imply that the layered polar ice deposits would be trending acidic? (Acidic dust [from acid sulfates] + ice)?

-Mike

Mike - As you note, a tiny spring involving a very small groundwater system isolated from the usual rocks might be acid, and your list of possibilities is certainly not inclusive. Small springs draining an oxidizing sulfide deposit (mine dump model) or hot springs above a boiling magma or brine (volcanic or impact melt-driven) could also be acidic, as mentioned above.

Regarding polar ice, great question! One way to prevent acidic water from reacting with basic rock is to freeze it. This was noted by Roger Burns for Mars; a possible terrestrial analog is the surge of acid that accompanies spring snowmelt in the Rockies where there are lots of old mine dumps and acid dust has accumulated over the winter. So spring ice melt on Mars could also well be acid, and could have contributed to the acid sulfates you see on the surface. Once the acid ice melt had percolated into the brecciated regolith, however, one would expect it to be neutralized, much as acid rainwater is on Earth as it becomes groundwater. Minerals of the jarosite group typically form during partial neutralization of iron-rich acid waters by alkali-bearing rocks, forming a yellow-brown stain downstream from mine dumps. Jarosite on Mars might have formed by such a frost melt/partial neutralization mechanizm, without requiring a strongly acid atmosphere or or groundwaters (unlike what others have proposed).

Related to freezing, one way to make strong sulfuric acid on Mars is by mostly freezing weakly acid waters (fractional crystallization). The brine that's left should be enriched in sulfuric acid, which is very difficult to freeze. (Much like concentrating the alcohol in beer or wine by partly freezing it - what you might call a "Siberian Still".) This could only happen in complete isolation from the basaltic regolith, however, a fact which the people who have proposed this mechanism for Mars conveniently ignore (although you clearly thought of it).

Thanks for the discussion, but tomorrow I'm off to look at basaltic volcanism in Hawaii for a week or so. (And I hope return air fares don't double in cost while I'm there.) Please save further questions for my return, or let someone else answer them.

-- HDP Don

All rocks tend to buffer acid waters, not just basalts.



On Earth, acid springs occur in environments where acid is begin generated faster that it is consumed. For example by input from volcanic gases or by weathering of sulphides.

On Mars weathering of sulphites (which may be common) to sulphates would also work to cause surfical acidity.

Jon