[X] My Assistant

[Juramike]

We'll soon know what kinds of crops we can grow on Mars! Bonus, the fruits will be already freeze-dried!

Handy list of preferred pH's of common garden plants.

-Mike

[CosmicRocker]

That's really a difficult question to answer, considering the actual Martian data that we have to work with.

[djellison]

'Don't know, it'll be interesting to find out'. Tick.

[Doc]

Considering the fact that there is water ice and some salt, basic minerals, I think we can make a rough assumption about the pH value of martian soil.
However the verdict is still open.

[tuvas]

My money is on fairly acidic.

[BrianL]

Oh man, my camp is dead last! The curse of the far side continues...

Brian

[centsworth_II]

The results indicate that, as a group.... we don't have a clue!

[peter59]

The robotic arm has just delivered the first sample of soil to Wet Chemistry Laboratory.

[Cargo Cult]

The universe's first, interplanetary Pot Noodle?

[djellison]

Poll = Fail

The results from the first sample are a pH between 8 and 9

Doug

[elakdawalla]

News: WCL analysis indicates pH of "8 or 9." Very surprising!

--Emily

[tedstryk]

Someone spilled the baking soda....that explains all the bright patches Phoenix is seeing - Stu, you have your answer!

[Juramike]

Someone spilled the baking soda....that explains all the bright patches Phoenix is seeing - Stu, you have your answer!

Nope. Not baking soda. That would hit a pH of 7 (neutral). More like sodium carbonate.

Looks like we'll be sipping soothing mint tea on Mars...

-Mike

(P.S. my guess was at the other end of the pH scale)

[Bill Harris]

Not surprising. The pH is a rather quirky parameter that is also temperature dependent (although that may not be entirely relevant here). The WCL takes a sample of the regolith/soil and introduces it to water at an un-martian temperature. I get many hits to "phoenix pH WCL" and need to sort through them.

My first thought is that the high pH is from hydroxyl ions, but we'll need to see the entire chemistry to figure out what is happening.

Here is a quick-and-dirty explanation of pH _vs_ temperature:

http://www.lenntech.com/Correlation-betwee...Temperature.htm

which, again, may not be entirely relevant here.

--Bill

[TheChemist]

High -OH does not have to be present in the original sample.
A simplified view :
High pH means that the salts involved have a "weak acid" part, thus anions that form strong acids are probably low concentration in the sample:

Cl-, Br-, I-, SO4--, NO3-, ClO3-, ClO4-

As Mike said, CO3-- (carbonates) or any other weak acid would be a good candidate.

Remember this is a real sample, with many salts probably present so common ions effects might also be present.

Let's wait and hear what the Phoenix team's martian experts will say !

[djellison]

Poll now closed, because that would be like...cheating


Doug

[tedstryk]

Nope. Not baking soda. That would hit a pH of 7 (neutral). More like sodium carbonate.

Baking soda has a pH of 8 or 9.

[Juramike]

Baking soda has a pH of 8 or 9.

I stand adjusted.

I made a basic error.

<ducks>

[ugordan]

I made a basic error.

Lol.

[dburt]

High pH means that the salts involved have a "weak acid" part...
As Mike said, CO3-- (carbonates) or any other weak acid would be a good candidate...

May not be relevant here, but silica (SiO2) itself can be considered a weak acid, so that just freshly pulverized basalt (probably a major component of martian sand) will yield a mildly basic solution in contact with liquid water. You don't need a basic "salt" as such - any basaltic silicate mineral, olivine or pyroxene or plagioclase feldspar, will do.

-- HDP Don

[Airbag]

Poll now closed, because that would be like...cheating

Doesn't matter much, since a pH of 8-9 was not one of the choices anyway

Airbag

[TheChemist]

DOI: 10.1306/74D70E75-2B21-11D7-8648000102C1865D
Dissolved Products of Artificially Pulverized Silicate Minerals and Rocks: Part II
W. D. Keller, A. L. Reesman
Journal of Sedimentary Research
Volume 33 (1963)

ABSTRACT

Indeed, slightly basic pH (8.2 to 9.2) is reported by these authors for most silicate rocks.
More recent literature anyone ?

PS. It seems we were all biased by the "past acidic conditions" and the tons of sulfates at Meridiani :-)

[Juramike]

I was biased by the prospect of acidic windblown dust or salts making up the top layer of the surface.

I guess that didn't pan out.

<ducks and runs for cover>

[fredk]

It seems we were all biased by...

Except those of us who can barely remember from school which side of 7 is basic and which side is acidic, nevermind guessing what the conditions on Mars might be!

It may be worth stressing that at the briefing they pointed out that conditions may vary considerably with depth or with location on Mars. Today's result is likely just one data point rather than "the answer" to what the pH is on Mars.

[Cargo Cult]

Apparently we're all going to be eating asparagus on Mars.

Stinky urine, anyone?

Edit: that article has some ... interesting units. A cubic metre of soil? Blimey!

[djellison]

"The 1 cubic meter (35 cubic feet) of soil was taken from about 1 inch below the surface of Mars and had a pH, or alkaline, level of 8 or 9. "

Oh boy. Did they take the cartoon of Phoenix burying itself seriously ?

Doug

[Cargo Cult]

Oh boy. Did they take the cartoon of Phoenix burying itself seriously ?

Emily's blog is, as ever, far more informative - and suggests it was a cubic centimetre of soil sampled.

Oh well, Reuters was only out by six orders of magnitude. ;-)

[JRehling]

The free-style mixing of standard units and metric ought to be blacklisted in Mars exploration PR.

Some people -- you give 'em an inch, and they'll take a hectare.

[ngunn]

I agree. Non-metric has to go. It just acts as a fog.

I mean, Fahrenheit - for goodness sake spare us . . .

but save the pint! (no impact on science).

[BrianL]

but save the pint! (no impact on science).

Well, save the Imperial pint. The US pint has got to go.

Brian

[bcory]

Apparently we're all going to be eating asparagus on Mars.

Stinky urine, anyone?

Edit: that article has some ... interesting units. A cubic metre of soil? Blimey!

That article left out half his sentence though...

"Preliminary results showed the soil had a pH between 8 and 9, researchers said. A pH less than 7 means the solution is acidic, while a pH over 7 means it is alkaline. Phoenix also detected the presence of magnesium, sodium, potassium and chloride in the mixture.

"It's very typical of the soil here on Earth minus the organics," Kounaves said during a teleconference from Tucson, Ariz.

On Earth, asparagus, green beans and turnips could be planted in such an environment and chemical-loving bacteria would thrive there, he said.

Planetary scientist David Paige of the University of California, Los Angeles, said it is too early to tell whether the minerals found in the soil could support life. Paige, who had no role in the mission, said the find was not surprising because rocks weather over time and bits of minerals mix with the soil."

http://news.yahoo.com/s/ap/20080626/ap_on_...3uBRCTV7nL0kPUI

[siravan]

What does a pH of 8-9 do to the "missing carbonates" paradox? If there was liquid water on the surface of the Mars at some point of time and CO2 in the atmosphere, then pH 8-9 (in contrast to an acidic pH most of us expected) is ideal for precipitation of carbonates (e.g. limestone). Where are all those carbonates?

[Juramike]

Apparently we're all going to be eating asparagus on Mars.

From the article:
"When told the pH levels, one colleague 'jumped up and down as if he had the winning lottery ticket,' mission soil analysis specialist Michael Hecht told a telephone news conference."

Evidently he was in the UMSF poll.

[Stephen]

Non-metric has to go. It just acts as a fog.

Careful! It's an American mission. If they get antsy it'll more likely be the metric measures which will get scrapped, in which case you guys are going to have to learn to live with feet and miles as well as inches.

Some people -- you give 'em an inch, and they'll take a hectare.

Mixing measures of length with measures of area in your metaphors serves only to confuse rather than to clarify.

======
Stephen

[ngunn]

Note for admin - the top quote in post 34 there is mis-attributed, not sure how that can happen.

Strange - somebody must have got there units mixed up - I've fixed it - James

[ngunn]

Back on the pH, I have a question for the chemists. On Earth clays in soil act as pH buffers. Is this only because of their associated organics, or would organic-free martian clays be expected to do the same?

[TheChemist]

Just to clarify things I wrote earlier in this thread: the fact that the pH of the first soil sample was 8-9, i.e. slightly basic, does not mean that the main salts present are carbonates, phosphates or whatever other "weak acid" anions. The first results from the team, also mentioned in the nice sum up in Emily's blog, show they found Na+, Ca+, K+, and Cl-, and are currently measuring the levels of sulfates, SO4--
Combinations of the above ions form salts where both ions are very soluble in water, and thus, do not alter the original pH of the water brought from earth, which was 7, although they might be the main salts in the soil concentration-wise. Basic salts could be just a very small proportion, or even absent if martian basaltic silicate minerals in sand have a slight alkaline pH, as mentioned by D. Burt.

[Juramike]

Back on the pH, I have a question for the chemists. On Earth clays in soil act as pH buffers. Is this only because of their associated organics, or would organic-free martian clays be expected to do the same?

Buffers can be either inorganic and organic.

So an inorganic salt could be a buffer (example: sodium bicarbonate solution).

Hydrate complexes formed by cations (K+, Mg++, Ca++, etc.) dissolved in water also have their own pKa's (and pKb's) and could also act as buffers.

-Mike

[nprev]

Hmm. What does this tell us (if anything at all) about the existence of superoxides at the site? Straining my memory of ancient high-school chemistry here, I would expect such compounds to be aggressive electron donors & therefore acidic.

(Okay, now tell me I got that backwards. Plus, I know it's a subsurface sample, but you'd expect this stuff to get circulated down at least a couple of cm due to wind action over time.)

[Juramike]

Hmm. What does this tell us (if anything at all) about the existence of superoxides at the site? Straining my memory of ancient high-school chemistry here, I would expect such compounds to be aggressive electron donors & therefore acidic.

Yup. The pKa of hydroperoxy anion (HOO-) is 4.88 (acidic like vinegar). So at any pH above 5, the predominant form will be the superoxide anion (O2--)

At pH 9, the ratio of superoxide anion to hydroperoxy anion will be about 10,000 : 1.

(Source: Wikipedia/superoxide + others to confirm)

-Mike

[dburt]

Hmm. What does this tell us (if anything at all) about the existence of superoxides at the site? Straining my memory of ancient high-school chemistry here, I would expect such compounds to be aggressive electron donors & therefore acidic...

As you feared, you actually have it a little reversed. An oxidizing agent like oxygen gas, peroxide ion, or superoxide ion wants to gain electrons (be an electron acceptor) - all want to turn into the oxide ion, O2-. A reducing agent like iron metal wants to lose electrons (be an electron donor), to either the ferrous ion Fe2+ or the ferric ion, Fe3+. Combine them and you get either FeO (wustite) or Fe203 (hematite). Oxidizing and reducing are clearly relative terms, because an ion like Fe2+ can either be oxidized to Fe3+ or reduced to Fe metal.

Regarding acids, by the electronic (Lewis) definition of acids and bases, an acid is electron pair acceptor, generally with a large charge to radius ratio (the ultimate acid is the tiny naked proton H+), whereas a base is an electron pair donor (e.g., the oxide ion, O2-, which has a pair of electrons to donate). Combine them and you get neutral H2O or water. In aqueous solution, these two ions are unstable - the proton combines with a water molecule to form H3O+ (hydronium) and the oxide ion takes on a proton to form OH- (hydroxide). By common convention (acidic and basic, like reducing and oxidizing, being relative terms in a continuum), an aqueous solution with an excess of hydronium is called acidic and one with an excess of hydroxide is called basic.

As you correctly recalled, there is some overlap between the definitions of oxidized and acidic, and between reduced and basic, inasmuch as both definitions involve electrons and ionic charge. This is accounted for in the so-called Usavovich definition, only rarely used by geochemists, which does not differentiate between oxidizing agents and acids, or reducing agents and bases. A familiar example of its importance is to compare the acid strength of reduced hydrogen sulfide H2S (very weak) with that of oxidized sulfuric acid H2SO4 (very strong). That is, if it's oxidized, its generally more acidic, as you correctly you pointed out.

Relevance to Mars? That's a longer story, and this post is already too long.

-- HDP Don

[dburt]

What does a pH of 8-9 do to the "missing carbonates" paradox? If there was liquid water on the surface of the Mars at some point of time and CO2 in the atmosphere, then pH 8-9 (in contrast to an acidic pH most of us expected) is ideal for precipitation of carbonates (e.g. limestone). Where are all those carbonates?

No one else has dared to tackle this, one of the biggest unanswered questions of Mars, so I'll foolishly try. One common hypothesis is that the ancient martian atmosphere was very different from today's, owing to a very high content of volcanic sulfur dioxide, itself caused by extremely active volcanism in the past. By this hypothesis, the acidification of surface waters by the atmosphere rendered deposition of carbonate rocks impossible. This would imply that the rate of absorption of acid species from the atmosphere always greatly exceeded the rate of neutralization of those acid species by the pulverized basic rocks of the martian crust. One chemical problem with this hypothesis is that seasonal or permanent ice cover on Mars would completely cut surface waters off from contact with the acidic atmosphere, allowing neutralization by reaction with rocks, at least seasonally. Another one is that surface waters on Earth (I know, terrestrial analogs are dangerous for Mars) are only rarely acidic, despite all the acids (carbonic, sulfuric, and nitric) constantly being tossed into the atmosphere by our civilization, not to mention our extremely active volcanism (compared to Mars). The implication is that surface rocks (on Earth at least) generally buffer the pH of surface waters to neutral or basic, even without an ice cover, and with active volcanism, coal-burning power plants, smelters, and so on.

Another common hypothesis, a far simpler one, is that, owing to low pressures and low temperatures, liquid water on Mars was always somewhat transient. That is, if present, it never stuck around long enough to reach chemical equilibrium with either surface rocks or the atmosphere, and thus to precipitate appreciable quantities of carbonates (other than the minor quantities found along fractures in some meteorites from Mars). Offhand, I'm not aware of any chemical problems associated with this hypothesis, but you may be. Also, keep in mind that the two hypotheses need not be mutually exclusive (that is, you could logically have a sulfur dioxide-rich ancient atmosphere, or any other ancient atmosphere, and transient or no liquid water at the same time).

Anyone else have any thoughts?

-- HDP Don

[Bill Harris]

pH is a quirky parameter and we may be putting too much stock in this value. I do wish that the media would stop proclaiming "conditions favorable for life" when the conditions are simply "not hostile to life". I'll be wanting to see an anion-cation balance and Piper-Stiff diagrams (et al) when the full chemistry comes in. It's been centuries since I've done one manually, I'll need to unearth my textbooks...

--Bill

[elakdawalla]

It's not really the media's fault. The Phoenix panel came out of the gate with a story from Hecht about how he called a friend working in Antarctica and told her that they now knew what they needed to know about how to grow stuff in Martian soil, because they knew what "nutrients" were there. And then they seemed confused when the reporters asked, okay, what kind of life are you talking about? Viruses? Bacteria? Multicellular stuff? Plants? And they weren't prepared to answer. Finally they said the pH was compatible with asparagus, turnips, and green beans, and there was nothing incompatible about the soil. But they'd started talking about life, so the reporters were asking, what about the trace elements? What about organics? And of course they couldn't answer those questions, because they couldn't do those tests.

--Emily

[TheChemist]

I really wish the panelists were a bit more conservative and better prepared in this last press conference.
After all, we know that the popular media will exaggerate whatever they hear to infinite proportions.
The press here today is full of comments about how easily "you could grow asparagus on Mars that is as tasty as in our own garden".

[Bill Harris]

<sigh>, in a manner of speaking, this "Mars soil is yummy" comment... snowballed?

--Bill

[Juramike]

Well....in one sense the press has picked up on a key finding, if you look at it from the eventually-there-will-be-colonists-on-Mars in a "Farmer in the Sky" point of view: the results of the basic soil of this one analysis help bring Mars down to Earth. I can imagine what kinds of crops might be grown there someday.

The Big Three, NPK (nitrogen, phosphorous, and potassium), can be adjusted by large amounts of fertilizer, and trace micronutrients can also be easily added (I use Greensand) to soil. Soil microorganisms and plants can be coaxed to live as long as there aren't any wierd yukkies (funkybad salts like arsenic) or other reservoirs of difficult reactive species.

Soil pH, while adjustable, can be a pain to deal with. Ask anyone from Texas trying to grow acid-loving rhododendrons in alkaline caliche. You can do it, but you will be adding soil amendments forever. It is a losing battle, as the background soil will continually be trying to buffer out the tiny acid patch you've installed to grow your rhodys.

So when the full results of the soil analysis are complete, (and assuming no funkybad stuff) it will be possible to picture what bags of soil amendments and other materials would be required to mix into martian soil to make it suitable for agriculture.

I have no idea why, but I find that concept both fascinating and comforting.

-Mike

[nprev]

Mike, you consistently amaze me with your ability to coin great band names..."The Funkybad Salts" would definitely kick gluteus maximi!

Thanks to Don also for the illumination. From what I gather, a pH reading alone is not enough to extrapolate detailed chemical properties and compositional details on Mars, even when compared to mass spec data. It helps, of course, but it also seems too easy to apply terrestrial analogues too freely, 'cause that's what we know. MSR is a must.

[belleraphon1]

I have no idea why, but I find that concept both fascinating and comforting.
-Mike

Mike... so do I.... "The Farmer in the Sky" has just gotten a tiny bit closer to reality .....
To me this is like being in a hard science fiction story... and so much more to come.

Craig

[Bill Harris]

Well....in one sense the press has picked up on a key finding...

It's still looking better. The last "key finding" in '76 suggested a horridly reactive superoxide mix, and you can add the "salty" sulfates at Meridiani. I'd love to put a chunk of ice into the WCL.

At home, I have to "make" soil for my flower and wildflower gardens. Except for paltry 6" of organic "A" horizon, most of my soil is a clay soil derived from the weathering of Pennsylvanian sandtones and shales, so I have to add lime, organics, sand and nutrients to the mix.

--Bill

[Juramike]

At home, I have to "make" soil for my flower and wildflower gardens. Except for paltry 6" of organic "A" horizon, most of my soil is a clay soil derived from the weathering of Pennsylvanian sandtones and shales, so I have to add lime, organics, sand and nutrients to the mix.

I hear that. I've made a garden from Piedmont gray clay (like red clay but lacking in iron). 200 million years of NOT MUCH HAPPENING leached most the nutrients out of the native soil. And it's a natural pH 4.5 as well.

But I'll bet Mars doesn't have mosquitos, ticks, Japanese beetles, squirrels, or deer.

Sign me up.

[Shaka]

Daisy World, here we come!

[edstrick]

On a world with a probable history of a magma ocean and with well differentiated crust, mantle and core, one problem I've thought of won't be a problem.

Heavy metals.

Would the heavy metal content of a chondritic soil or more specifically a carbonaceous chondrite soil cause problems?

In California, there's serpentinite and related terrains formed of up-thrust mangled bits of upper mantle. Lots of plants DO NOT like to grow there. They have decidedly special biomes growing on them. CChondrite soils would be worse!

[Bill Harris]

I don't know much about heavy-metal content of chondrites. Do you have references?

Although the Mar's convective mantle engine appears to be inactive nowadays, it may have been more active earlier. And certainly Mars has been hot and is differentiated.

--Bill

[SickNick]

Full inline quote removed - Admin.

An Undifferentiated Chondrite would have much more heavy metal content. All those Siderophile and chalcophile elements are concentrated in the core of the Earth.

Also, look at the fundamental differences of Earth and Mars. However you look at the situation, the bulk density is different, the chemical activity is different. Mars is made of different stuff then Earth is, and then it evolved different again. Never make the mistake of assuming that Mars is "like Earth"...

[dvandorn]

That's sort of a matter of degree, isn't it, Nick? In the great range of like to unlike, Mars is far more like Earth than it is, say, like Jupiter. Or Neptune. Or even Titan.

-the other Doug

[jmknapp]

Just saw this article in the Telegraph:

Martian dirt is rich in nutrients and capable of sustaining Earthly life, such as turnips and asparagus, surprised scientists announced.

But as I understood the press telecon, they've found certain trace elements, not all the nutrients necessary for growing plants (i.e., NPK). Seems like the press is being "led down the garden path" by these press conferences.

[Juramike]

Major elements and trace elements (in order), required for plant growth:

C. HOPKNS CaFe Mg B Mn CuZn ClMo

("C. Hopkins Cafe, managed by mine cousin Clomo.")

It will be really interesting to see the quantitification of trace elements detected (I assume in ppm).

And if there are heavy metals? No problem. Just plant ferns just before your martian bean crop as in this article/video.
(Bad luck that most ferns are acid-loving, but maidenhair ferns like pH 7-8)

-Mike

[antipode]

The bizarre flora of long isolated New Caledonia is a fascinating example of long term adaptation to soils rich in often nasty heavy metals and other baddies.

p

[nprev]

...cool mnemonic, Mike!

This whole spin-up is a bit unfortunate, though; expecting to be bombarded with questions from my co-workers tomorrow (been gone for the last 2 weeks attending a class). After all, plants have been grown in lunar soil, but that does not imply that life arose on the Moon, merely that terrestrial life needs certain stuff to exist & the Moon happens to have it. Big difference.

[Ipparchus]

Irrelevant and full in line quote of last post removed.


Did they deliver at the weekend a sample to the optical microscope or to the Wet Chemistry Laboratory? if not,when do they plan to do this?

[akuo]

There is a dark image here, but by adjusting brightness and contrast, I think I can just see some material in the 2nd WCL cell:
http://phoenix.lpl.arizona.edu/images/gallery/lg_10401.jpg

I guess the RAC view is better :-)

http://phoenix.lpl.arizona.edu/images/gallery/lg_10339.jpg

There seems to be some stuff at least on the side of the collector, but I wonder if it's enough.

I presume this is from the soil/ice interface layer?

[bergadder]

"
July 7, 2008 -- NASA's Phoenix Mars Lander used its Robotic Arm to deliver a second sample of soil for analysis by the spacecraft's wet chemistry laboratory, data received from Phoenix on Sunday night confirmed. "


http://phoenix.lpl.arizona.edu/07_07_pr.php

[TheChemist]

Some tidbits from the July 1st entry of Dr Tom Pike's diary for the BBC News website :

"In particular, if the soil is alkaline this may go a long way to explaining the Viking experiment. Fifteen years ago, one of my Phoenix colleagues, Richard Quinn, worked out that just such a soil would explain the Viking results."

and

"The data streams down, filing up our computer screens with scans from all the sensors. There's a quiet smile on Richard's face as he concentrates on just one of these lines - the soil is just about as alkaline as he expected.

It looks like one of the biggest mysteries from previous missions to Mars has been cracked by Phoenix. It was the chemical reactions of nutrients with the chemistry of the soil, not life, that Viking saw back in 1976. "

Before touchdown, Dr. Quinn was quoted in an article at the SETI site :

When asked, "What would be the best possible outcome from these experiments?" Quinn replied, "A sample with high salt content and reasonable ph which would reveal a history of water, coupled with results from the Thermal Evolved Gas Analyzer that found organics in the soil." Then, you'd have both water and organics. Perhaps evidence of life?

So,
If the alkaline pH supports the "superoxides in soil" Viking explanation, why were teran gardeners encouraged to have high hopes for martian asparagus ? Anyone care to enlighten us ?

[marsbug]

I'd guess that the alkaline soil is one piece of evidence in favour of the superoxide idea, but there are a lot more to be found before it's proven- such as the superoxides themselves! Over simplified reporting, although i may be judging prematurely, having not read the thing..

Edit: now I've read it I think its less oversimplification, more two tentative interpretations on preliminary results, as always more data needed!

[gallen_53]

If the alkaline pH supports the "superoxides in soil" Viking explanation, why were teran gardeners encouraged to have high hopes for martian asparagus ? Anyone care to enlighten us ?

Perhaps because it's easier to sell a Mars program as a "search for life" rather than as a "search for superoxides"?

[Shaka]

Unless you show that the latter "get your laundry superbright!! "


It's tough waiting for data.