Help - Search - Members - Calendar
Full Version: MSL - SAM and CHEMIN
Unmanned Spaceflight.com > Mars & Missions > MSL
Pages: 1, 2, 3, 4, 5
Astro0
ADMIN NOTE: Hi All, a new topic for the discussion of the science from the SAM and Chemin instruments.
There has been a very important amendment to Rule 1.3 which is explained here.
Please remember
Rule 1.3 at all times when discussing matters in this section.
pospa
MSL Status Report 11.20.2012:
"... Although Curiosity has departed the Rocknest patch of windblown sand and dust where it scooped up soil samples in recent weeks, the sample-handling mechanism on the rover's arm is still holding some soil from the fifth and final scoop collected at Rocknest. The rover is carrying this sample so it can be available for analysis by instruments within the rover if scientists choose that option in coming days."

If the latest SAM analysis result IS "one for the history books" then I would expect repeated measurement of the same sample.
Is there any indication of such a plan for upcoming days (in addition to first drilling)?


Fran Ontanaya
Something for reference: http://proceedings.spiedigitallibrary.org/...rticleid=786403
Don1
SAM is of course capable of detecting gases evolved from heated samples, and measuring the isotope ratios. Such gases would be expected to include CO2 and water, and possibly HCl or Cl2.
nprev
Mod note: Two posts discussing rule 1.3 changes moved here.
RonJones
I have not seen any specific statements from the Curiosity science team regarding the ability of SAM to detect organics if perclorates are present in a soil/rock sample. Since SAM first heats the sample up to a high termperature (e.g., 1000 deg.) to vapaorize the sample, would this not destroy organics if perclorates are also present in that sample? Since we have known about the potential for perclorates in the Martian soil since the Pheonix results reported in 2008, I asume this has been considered in some detail by the Curiosity team. Anyone have any information on what level of perclorates would be sufficient to cause significant problems for SAM being able to detect organics (I assume that would also depend on the level of organics in the sample)?
mcaplinger
QUOTE (RonJones @ Nov 22 2012, 12:35 PM) *
I have not seen any specific statements from the Curiosity science team regarding the ability of SAM to detect organics if perclorates are present in a soil/rock sample.

Have you read http://link.springer.com/article/10.1007/s11214-012-9879-z ?
QUOTE
The presence of perchlorates and other oxidants, if present in the martian soil and
rocks at Gale crater, could have implications for the SAM search for organics as some of
these compounds could be transformed to CO2 in the oven. If perchlorates are present, a small amount of the organics may form chlorohydrocarbons that could be detected by the SAM GCMS experiment. The presence of perchlorates
may also be indicated by O2 , HCl, or Cl2 evolution in a SAM EGA experiment or these
compounds may be detected by the ChemCam instrument. Similarly,
the presence of high concentration H2 O2 in sediments could manifest itself in the form of
formaldehyde or methanol, species that are potentially detectable by SAM.

nprev
One fascinating finding would be if perchlorates are not present in these first samples.

I rather suspect that there is considerable diversity in the composition of martian soil at the regional scale once you get beneath the ubiquitous wind-deposited global dust layer. Recall the serendipitous exposure of subsurface chemical deposits at Gusev by Spirit from the dragging wheel.
Burmese
No data yet to work with until they present their findings in Dec, however the news so far out of JPL is illustrative:

I think this announcement will be of relatively mild significance here, the fact that the scientists are even dropping hints at this stage is an indication that is the case. There have been elements and compounds that we are pretty certain are there on Mars and these are simply the 1st instruments capable of definitive proof. It is a feather in Curiosity's hat(hopefully the 1st of many), but just that, not a turkey on the table. That they plan to present the data at a science forum, and not at the typical news conference is simply intelligent planning. The audience will be of a caliber to hear the word 'organic' and understand the nuances inherent in that whereas, if they 1st say that word at a news conference full of reporters, that would be tantamount to yelling 'fire' in a theater and likely induce spontaneous combustion in the room.

If they ever encounter anything more significant, we won't hear word one coming from JPL for a long time, as the watchword would undoubtedly be one of Carl Sagans' better known pronouncements: "Extraordinary claims require extraordinary proof"
nprev
Very good comment, Burmese; thank you!

In general, findings of scientific significance tend to be deeply underwhelming to the general public. Strongly advise our members not to be swayed by the usual mass media sensationalism; they are, after all, trying to sell a product and therefore marketing takes precedence over accuracy and critical thinking.

We will find out what it is in due course. In the meantime...the journey continues!!! And it's barely begun. wink.gif

EDIT: Also, a word about organics.

It is overwhelmingly likely that at some point organic molecules will be detected by Curiosity. However, it is also overwhelmingly likely that most if not all of same came from carbonaceous meteorites, and we have seen both direct evidence of recent impacts on Mars from the orbiters as well as iron-nickel meteorites from the MERs. Bear in mind that compounds up to and including amino acids have been found in terrestrial meteorites; therefore, it is reasonable to expect the same sorts of findings from Curiosity as, over time, these objects have weathered and become incorporated into the martian soil.

Bottom line is that ANY discovery of organics means just that: Discovery of organics. Nothing less...and nothing more.
RonJones
I suspect that if any new finding by MSL would be of significant interest to the general public it would be announced at a NASA press conference rather than just with paper to a science conference. The findings expected to be disclosed in a couple of weeks may be very interesting to planetary scientists, but may be not be of such a nature to be understood or appreciated by the general public. Let's wait and see if NASA schedules a press conference before the start of the conference.
Astro0
ADMIN NOTE: Can I remind everyone that this thread is for "Discussion of the science/results from these instruments" and not for debating why, how or when information will be/should be released, etc. This thread was opened with some very specific rules put in place and if it goes off-topic, will result in its closure and Rule 1.3 changed again. This was an attempt by the Admin Team to allow for discussion on a topic that has been 'out of bounds' in the past. It's up to members to make it work - if it doesn't then it's off the agenda forever.
marsophile
QUOTE (RonJones @ Nov 22 2012, 12:35 PM) *
...would this not destroy organics if perclorates are also present in that sample?


All you have to do is wash the sample in water before pyrolyzing it. That would remove water-soluble components like perchlorate while retaining hydrophobic organic substances if any are present. I was under the impression that Curiosity has this capability or something like it.
mcaplinger
QUOTE (marsophile @ Nov 22 2012, 08:54 PM) *
All you have to do is wash the sample in water before pyrolyzing it...I was under the impression that Curiosity has this capability or something like it.

Not that I'm aware of. SAM has its wet chemistry cells but the SAM instrument paper referenced above doesn't indicate that this is their purpose -- see section 4.6, "Solid Sample Measurements Based on Wet Chemical Processing".

Note that Springer-Verlag has made all of the MSL instrument papers free-access until the end of the year, so there's no excuse not to read up if you're interested -- http://link.springer.com/journal/11214/170/1/page/1
MrNatural

Can we discuss SAM's stereochemistry capabilities? I believe that SAM can sort out chirality, but I have seen very little written about this. As we all know, stereochemistry would allow us to help us determine, ah I hesitate to say this, the genesis of some organics. As far as I can tell, SAM can determine if a peak is chiral, but I am not sure if it can tell if there is a preponderance of L- versus D- for a particular organic chemical.
mcaplinger
QUOTE (MrNatural @ Nov 23 2012, 08:08 AM) *
Can we discuss SAM's stereochemistry capabilities? I believe that SAM can sort out chirality, but I have seen very little written about this.

First, ask in the SAM/Chemin thread. Second, read the SAM instrument paper. Third, do a simple google search for "sam msl chirality" and then you will be prepared enough to ask questions.
elakdawalla
Actually they're only free through Nov 30 -- one more week. Get 'em while they're hot.
marsophile
QUOTE (marsophile @ Nov 22 2012, 08:54 PM) *
... or something like it.


Thanks very much for those links, especially this one:

http://link.springer.com/article/10.1007/s...z/fulltext.html

This image from the above link illustrates what I was trying to recall:

Click to view attachment

There are chemical solvents that can separate possible organics from the sample before heating, and also there is initial heating at a lower temperature.
Don1
SAM has a number of different modes of operation. The most common mode is going to be evolved gas analysis. On heating minerals like carbonates, sulfates and perchlorates will decompose, yielding gases like CO2, SO2, Cl2 and HCl. Water trapped in the crystal structure of minerals will also be driven off. SAM has a lot of capability to measure the isotope ratios for CO2 and H2O. If those isotope ratios differ from those of gases in the present Martian atmosphere, that will be an interesting result. The isotope ratios of Martian atmospheric gases have changed over time due to the loss of atmosphere to space. The isotope ratios of carbon and oxygen in carbonate minerals would be the same as that of the atmosphere at the time of their formation.

What about organics? If both organics and perchlorate are present in the soil SAM would see chlorohydrocarbons. If the soil at this site is different from the rest of Mars, then organics might be present without perchlorate. In that case SAM would detect the breakdown products of the organics. Detection of organics would certainly qualify as earthshattering, but the Martian surface is known to be a hostile environment for them.

If organics are suspected, I would expect a second run of SAM, this time in the wet chemistry or derivatization mode. Only 9 of the 74 sample cups contain the wet chemistry reagent. This reagent can remove perchlorates, which enables the organics in the sample to be directly detected.

Given the speed at which things move on SAM, they probably haven't gotten around to doing wet chemistry yet. If they are in a hurry to do a second run on the same sample, that would point to organics.
Spin0
From AGU's 2012 Fall Meeting scientific program:
MONDAY, DECEMBER 03, 2012

Session: U13A
Results From Mars Science Laboratory Mission Four Months After Landing
1:40 PM - 3:40 PM

U13A-01. The Mars Science Laboratory Mission: Early Results from Gale Crater Landing Site (Invited)
John P. Grotzinger; Dave Blake; Joy A. Crisp; Kenneth S. Edgett; Ralf Gellert; Javier Gomez-Elvira; Donald M. Hassler; Paul R. Mahaffy; Michael C. Malin; Michael A. Meyer; Igor Mitrofanov; Ashwin R. Vasavada; Roger C. Wiens

U13A-02. Overview of the Atmosphere and Environment within Gale Crater on Mars (Invited)
Ashwin R. Vasavada; John P. Grotzinger; Joy A. Crisp; Javier Gomez-Elvira; Paul R. Mahaffy; Christopher R. Webster

U13A-03. First results from the CheMin, DAN and SAM instruments on Mars Science Laboratory (Invited)
David F. Blake; Paul R. Mahaffy; Igor Mitrofanov

U13A-04. The Radiation Environment on the Martian Surface and during MSL’s Cruise to Mars (Invited)
Donald M. Hassler; Cary Zeitlin; R F. Wimmer-Schweingruber

U13A-05. Chemical Composition of Rocks and Soils at Gale Crater, Mars (Invited)
Roger C. Wiens; Ralf Gellert; Sylvestre Maurice


Unfortunately the session is not on Video On-Demand Lectures and Sessions list. huh.gif
elakdawalla
Provided there's wi-fi or cellular signal, I'll be live-tweeting it!
vjkane
QUOTE (elakdawalla @ Nov 26 2012, 09:43 AM) *
Provided there's wi-fi or cellular signal, I'll be live-tweeting it!

Thank you for being there, Emily! This is the first year in several I won't make AGU (conflicting conference), and I already have anticipatory withdrawal symptoms.
Holder of the Two Leashes
QUOTE (Don1 @ Nov 23 2012, 10:49 PM) *
On heating minerals like ... perchlorates will decompose, yielding gases like ... Cl2 and HCl.


You sure about this? I was under the impression that mineral perchlorates (calcium and magnesium) would normally decompose by heating into the chloride salt and oxygen. There might be some HCl from the calcium perchlorate if it is the tetrahydrate, but I wouldn't expect to see Cl2 at all. Maybe I'm wrong.

Update: Right about the O2, wrong about the Cl2. See discussion below. The reaction Mg(ClO4)2 -> MgCl2 + 4O2 does occur as part of the mix, and occurs at a higher rate under earth atmospheric pressure as opposed to a vacuum. The other decomposition reaction branch (which produces chlorine) is 2Mg(ClO4)2 -> 2MgO + 2Cl2 + 7O2.
serpens
I would suspect that the end products (and intermediate stage products) would depend on the makeup of the total sample and associated hydration states. For say pure Mg perchlorate the end product would (I think) be MgO, Cl2 and O2. If Ca perchlorate is present and depending on hydration state then HCl should be a stage product which would react to give CaCL2 and CO2. But I stand to be corrected.
Don1
QUOTE (Holder of the Two Leashes @ Nov 26 2012, 11:08 AM) *
You sure about this? I was under the impression that mineral perchlorates (calcium and magnesium) would normally decompose by heating into the chloride salt and oxygen. There might be some HCl from the calcium perchlorate if it is the tetrahydrate, but I wouldn't expect to see Cl2 at all. Maybe I'm wrong.



I'm not sure about the Cl2. Sounds like you know more about this than I do!
mcaplinger
http://www.lpi.usra.edu/meetings/lpsc2012/pdf/2008.pdf and various other abstracts coming up with a google search for "sam msl perchlorate" may be of interest.

QUOTE
The parent salts of the perchlorate on Mars are unknown, but geochemical models using WCL data support the possible dominance of Mg-perchlorate salts. Mg(ClO4)2•6H2O is the stable phase at ambient martian conditions, and breaks down at lower temperatures than carbonates giving off Cl2 and HCl gas. Devlin and Herley report two exotherms at 410-478°C and 473-533°C which correspond to the decomposition of Mg(ClO4)2. They support a two-stage process:
(1) 2Mg(ClO4)2 = [MgO•Mg(ClO4)2] + Cl2 + 3.5O2
(2) [MgO•Mg(ClO4)2] = 2MgO + Cl2 + 3.5O2
If the chlorine gas produced reacts with moisture in the system or if the magnesium perchlorate has not fully dehydrated, then HCl gas can form and react with a carbonate phase to evolve CO2:
(3) CaCO3 + 2HCl = CaCl2 + CO2 + H2O
belleraphon1
AGU Press Conference Schedule:
http://fallmeeting.agu.org/2012/important-...edia-advisory-4

There is a Curiosity briefing (the first one) December 3 at 9:00 am PT.
Mars Rover Curiosity's Investigations in Gale Crater
Monday, 3 December 9:00 a.m.

NASA's newest Mars rover, Curiosity, has been investigating past and modern environmental conditions in Mars' equatorial Gale Crater since August. This briefing will offer findings from examining the composition and textures of targets touched by the rover's robotic arm. Curiosity is the car-size rover of NASA's Mars Science Laboratory mission. At the time of the AGU Fall Meeting, it will be four months into a two-year prime mission.
Watch live here: I don't you need to be registered???
http://live.projectionnet.com/agupress/fm2012.aspx

Edited to remove copy/paste formatting.
ADMIN NOTE: All, please either edit these down or only post a link to the original.
serpens
QUOTE (mcaplinger @ Nov 27 2012, 06:21 AM) *
http://www.lpi.usra.edu/meetings/lpsc2012/pdf/2008.pdf and various other abstracts coming up with a google search for "sam msl perchlorate" may be of interest.

Thanks for the link and as expected I stand corrected on the Ca perchlorate decomposition products. The sheer volume of information on the web is daunting but I couldn't find anything on analysis of mixed samples reflecting candidate martian perchlorates/soil compositions? I seem to remember that the thermal stablility of a mix of perchlorates is lower than that of the pure components and the initial endothermic reaction in the figure 1 Wicked Witch sample seems closer to that for Ca perchlorate. Curiosity's investigative capability is remarkable and I can't wait for the next LPSC.
Lucas
Well, this is interesting... apparently all the hype was simply due to a misunderstanding by the NPR reporter who was interviewing Dr. Grotzinger!

http://www.slate.com/blogs/the_slatest/201...out_entire.html

A tweet by Curiosity (screenshot attached) was meant to reduce the expectations and clarify Dr. Grotzinger's remarks, but apparently it wasn't noticed and the story went viral.

Sigh...

--Lucas
fredk
It certainly does look like bad reporting, at least in part. Remember that the word "earthshaking" was used in the original npr story. However, it was not directly quoted to Grotzinger. Now that word has been quietly changed to "remarkable".
EdTruthan
Press release on the Dec. 3rd AGU press conference in San Francisco just posted here. The gist of the statement reads:

"Rumors and speculation that there are major new findings from the mission at this early stage are incorrect. The news conference will be an update about first use of the rover's full array of analytical instruments to investigate a drift of sandy soil. One class of substances Curiosity is checking for is organic compounds -- carbon-containing chemicals that can be ingredients for life. At this point in the mission, the instruments on the rover have not detected any definitive evidence of Martian organics."
marsophile
I have video but no audio of the press conference. It appears from the graphics that chlorinated hydrocarbons have been detected. Those were also detected by Viking almost 40 years ago but were attributed then to contamination by cleaning fluids.
fredk
Details at the press release if anyone hasn't seen it already.
dvandorn
And yet the media still hear what they want to hear...

Huffington Post - Curiosity Finds Evidence of Organics on Mars

sigh...

-the other Doug
Hungry4info
Well, in fairness, they did say they detected simple organics, but they couldn't be sure it wasn't from the rover.
silylene
The chlorinated methanes are interesting. CH3Cl, CH2Cl2, and CHCl3 were detected.

If the starting C-containing material was CO2, somehow the C would have to be reduced, and a source of H would also be needed (from the decomposition of water, presumably?). It is not a simple process to reduce the C in CO2. However, i want to point out that some metal oxide dusts can function as capable catalysts for CO2 reduction (this is an active area of chemical research!).

For example a potential heat assisted catalytic cycle using a metal oxide, (unbalanced reaction):
H2O + CO2 + MOn + heat --> H2 + CH4 + CO + MOn+2
MOn+2 + heat --> MOn + O2

The CH4 is then subject to free radical chlorination, from a perchlorate origin.

Did the press conference presentation say whether they also detected CH4 or CO ? If my above mechanism is correct, then CH4 should have been found too, probably in greater amounts than the CH3Cl. If not, why not? I doubt that CH4 was not present if the chlorinated methanes were seen. I do note that they did detect O2. Of course the O2 could have come from the perchlorate, or my mechanism, or both. Someone needs to do a careful mass balance !

I may need to work out an alternate pathway using a sulfur compound as my reducing agent. The link does say that sufides may have been involved, these can be oxidized to SO2. H2S and SO2 were detected. NASA release

Now I can understand why Grotzinger got excited: Perhaps he at first thought he had a biogenic source of CH4. But abiogenic sourced CH4 is much more likely, in my opinion, perhaps via a reaction pathway similar to this outline.
serpens
QUOTE (dvandorn @ Dec 3 2012, 07:59 PM) *
And yet the media still hear what they want to hear...


Or maybe the fault lies with the left hand right hand disconnect from the team rather than with the media.

Paul Mahaffy, SAM principal investigator said "SAM has no definitive detection to report of organic compounds,"

John Grotzinger said "Even though [Mahaffy's] instrument detected organic compounds, first of all we have to determine whether they're indigenous to Mars"

Did they get a definitive detection of organics or not? Perhaps the British approach of a nice cup of tea and a chat to agree the findings would be beneficial. Organic molecules from infall would be expected, effectively compulsory, although the use of terms like 'indigenous to Mars' give rise to unfortunate implications for provenance.
MahFL
QUOTE (dvandorn @ Dec 3 2012, 06:59 PM) *
And yet the media still hear what they want to hear...

Huffington Post - Curiosity Finds Evidence of Organics on Mars

sigh...

-the other Doug


Why the sigh, they report accurately in the article the current situation. Everyone needs a headline, that is what pays their mortgage......
mcaplinger
QUOTE (serpens @ Dec 3 2012, 03:07 PM) *
Paul Mahaffy, SAM principal investigator said "SAM has no definitive detection to report of organic compounds,"

The press release says "We have no definitive detection of Martian organics at this point, but we will keep looking in the diverse environments of Gale Crater," said SAM Principal Investigator Paul Mahaffy..." (italics mine.)

The question is whether any detected organics are from instrument contamination or from the surface. Presumably at some point they will run the Organic Check Material through the system to address this.

I agree that this has not been a PR triumph. IMHO the best course would have been to say nothing until there was more definitive news, but with media attention this is easier said than done.
nprev
The discontinuity seems to be:

1. "Organics" was not precisely defined. That's a charged word, obviously. However, they did effectively communicate the fact that complex organic compounds most likely have meteoritic origins till proven otherwise, and even cited the recent Messenger findings on Mercury as an evidence that such compounds are far from uncommon throughout the Solar System.

2. The 'organics' thought to be detected seem to be most likely evolute products from the sample heating (i.e., chloronated methane). Several references to 'single carbon' compounds...well, so is CO2. Judgement call.

Bottom line from my perspective: SAM & the other instruments seem to be working well. This was pretty much a first-grab sample from a dune, so not much should be expected given that dunes usually consist of windborne (not necessarily local) material; it's gonna be light stuff no matter what.

Now let's see if we find some phyllosilicates... smile.gif



Antonb
Not only was 'organic' not precisely defined in yesterday's conference, the word cannot be defined with any scientific precision. Organic originally meant relating to an organism, a living entity. These days, people most often see the word organic on meat & veg in the supermarket. Has anyone ever seen an inorganic cow or cabbage?

Astronomers say there are organic compounds to be found all over the universe, even in the rocks that fall from space onto Earth, Mars and everywhere else, but they don't intend to imply that these originated in an organism. Yesterday's NASA press release defined organic compounds as "carbon-containing chemicals that can be ingredients for life". There is no scientific consensus behind this definition. For some, if a compound includes carbon, it's organic. Others require a C-H bond, but then that excludes common bodily compounds such as urea. As if that weren't confusing enough, astronomers don't call CO2 an organic compound, even though it's unquestionably a carbon-containing chemical that's an essential ingredient for life.

To be fair, I thought yesterday's conference did an excellent job explaining that the various compounds detected could have numerous explanations and that only painstaking, patient, scientific method will determine the answer. The co-ordinated, multi-instrument analyses they revealed are a spectacular achievement, but you could sense there was some discomfort and embarrassment on the platform, especially when the press kept returning to that darn word organic.

This linguistic inexactitude is the root cause of the wild speculation about "Life on Mars" that springs up just as soon as the word organic is mentioned. The word is functionally useless in any scientific context. Worse yet, it's not even necessary.

Among the many things that the MSL team have discovered so far are carbon compounds. They cannot yet say whether these carbon compounds are biotic or abiotic in origin.
JRehling
If you currently do a Google News search for "mars curiosity" it's easy to browse headlines, and the contradictory takeaways this event produced are evident. While the main articles may or may not converge by giving the same nuanced explanation, the headlines swing wildly from "detects 'organic compounds'" to "sees... no organics." Yesterday, in the body of one article, I saw a claim that the organics might have been brought to Mars by Curiosity (which is right) but then added the possibility they were brought by some previous spacecraft, which given the distances between landing sites is outrageously wrong and suggestive of something wild!

My dog used to take any jingle of my keys as a sign that we were going for a walk, and would become agitated and persistent if she heard the jingle. It didn't take me long to learn not to jingle them unless a walk was imminent. The scientific establishment would do well to know how the dog (media, public) responds to jingle and to act accordingly. In this busy, information-packed world, headlines have a powerful currency, we must all choose which headlines we read past and which we learn from, and this was, as others have noted so well, a case which was treated appropriately when the scientists had time in a panel discussion to explain things clearly, but the first "jingle" was careless.

I understand why there's excitement around the mere detection/non-detection of carbon in martian soil, but at the same time, carbon is the THIRD most abundant element in the solar system if you exclude helium (which is certain not to be a major bulk component of Mars) and the second most abundant element in Mars's atmosphere. In fact, there have to be some damned good reasons if we don't find any carbon in martian soil, which there obviously are (on Earth, as well, it is only 15th in crustal abundance). Which is just to say that finding it or not should have been (and should be, going forward) flagged in advance as a possible media event to treat according to a sensible key-jingling protocol. Without the team ever having misled anyone in a deliberate sense, there was a real, though unintended head-fake of the first degree here. News!?!?!? No, not in the sense that grabs first-page headlines. And the trust and attention erodes a little bit.

Meanwhile, Venus Express may have found signs of a volcanic eruption on Venus, and hardly a whisper in the news... In the (striking!) event that in one week we have news concerning one substance or another at all three planets in the inner solar system, I'd say the Mercury case was handled perfectly, the Venus one with too little hoopla, and the Mars one with far too much.
Fran Ontanaya
Can we go back to discussing the actual results. None of these science vs media issues are new. Most people I know expected the "stuff that isn't like boring rock minerals", and that's what they announced.
marsophile
For some context, we had the following results from the Viking GCMS.
Sample T Compound Abundance (ppb)
VL1
Blank Test 500 CH3Cl Not Detected
Sample 1 200 CH3Cl 15
VL-2
Blank Test 500 CH2Cl2 Not Detected
Sample1 500 CH2Cl2 2-6
Sample2 500 CH2Cl2 20-40

For a discussion, see this paper:
http://www.agu.org/pubs/crossref/2010/2010JE003599.shtml

The original Viking GCMS results were published in this Ph.D. thesis:
http://dspace.mit.edu/bitstream/handle/172...69/07517313.pdf

See for example, Pages 203 and 204 for VL-1 and VL-2 chlorinated hydrocarbon results.
(Methyl Chloride = Chloromethane, Methylene Chloride = Dichloromethane)
Also chlorinated hydrocarbon results from Antarctic soils Pp 233,242,250,258.
Don1
I think we're looking at a work in progress with the SAM results. They don't really have publication grade scientific results but they do have some very interesting data and hypotheses.

The most interesting is the detection of the chlorinated hydrocarbons, which are mostly chloromethanes. These showed up in Viking results on Mars, but were not seen in pre-flight tests of the Viking instrument. Chloromethanes are good solvents and cleaning agents. For instance CCl4 is used for dry cleaning. The Viking results were written off as contamination of the sample handling system by cleaning agents.

After the discovery of perchlorates, Chris McKay pointed out that a perchlorate containing soil would convert any organics it contained into chloromethanes on heating. He suggested that Viking did indeed detect Martian organics, but that the data was misinterpreted because the presence of perchlorate in the soil was unknown at the time.

I think the detection of chloromethanes by SAM puts a big question mark over the interpretations of Viking data, including the Viking conclusion that the Mars soil did not contain organics. The non-detection of organics by Viking was a very important result that drove the interpretation of some of the odd data produced by the other experiments.

However, SAM still has contamination issues of their own to sort out, including evidence that the rover is shedding plastic on the soil and hints that there might be a leak of organic reagent inside the instrument. People are also suggesting ways to make chloromethanes from purely inorganic reagents like CO2, water and perchlorate. So at this point there are viable hypotheses that explain the data without needing Martian organics. Only time will tell which is correct.
djellison
QUOTE (Don1 @ Dec 4 2012, 06:01 PM) *
I think we're looking at a work in progress with the SAM results.


Errr - obviously. They said as much yesterday.
serpens
QUOTE (Don1 @ Dec 5 2012, 02:01 AM) *
The most interesting is the detection of the chlorinated hydrocarbons, which are mostly chloromethanes. These showed up in Viking results on Mars, but were not seen in pre-flight tests of the Viking instrument.


As identified in the thesis linked by marsophile in post #44, (page 197) these chlorinated molecules were revealed in tests conducted on the spare flight instrument using the entire system. They would not have been seen in the pre flight oven checks or the flight blank tests and would only have contaminated a real run. Could additional chlorinated species have been produced as well as the contaminants? Certainly, and the SAM result indicates that maybe perhaps this could be so, but I think I want to see a heap more test results before drawing an conclusions or comparison to Viking results.

Re organic, none of us have problems with understanding homonyms in context , identical words with different meanings such as peer, rose, engaged etc. Lets all get over it.
marsophile
QUOTE (marsophile @ Dec 4 2012, 09:43 AM) *
Also chlorinated hydrocarbon results from Antarctic soils Pp 233,242,250,258.


What I find fascinating is that chloromethanes were detected by tests of the Viking GCMS in Antarctic soils.

Apparently these soils do also contain perchlorate:
http://pubs.acs.org/doi/abs/10.1021/es9033606

If this hint had been followed up, we might have hypothesized the presence of perchlorate in Martian soils a lot earlier.
dvandorn
QUOTE (marsophile @ Dec 5 2012, 11:03 AM) *
...If this hint had been followed up, we might have hypothesized the presence of perchlorate in Martian soils a lot earlier.

Well... perchlorate was one of the options that was being discussed at the time of the original GCMS experiments on Viking. The phrasing I recall is that the time-release experiment data fit well with a Martian soil rich in "super-oxidants," and one of the super-oxidants that headed the list was perchlorate. I believe the presence of chlorine in some of the evolved gasses seen in the Viking results is what led to that speculation, 36 years ago.

I don't have any articles of the time in front of me, but I am very confident of my memory of the "super-oxidant" reports.

-the other Doug
silylene
As I suggested in my prior post in this thread, I think the chlorinated methanes could have been produced from free radical reaction of the decomposition products of perchlorate with methane; with the methane formed in situ by the catalytic hydrothermal reduction of CO2 with high heat (oven max temp one oven = 950C the other oven = 1100C) over metal oxide containing dusts (certain metal oxide dusts can be catalysts for the hydrothermal reduction of CO2 to methane). H2O came from water adhering to silica grains. Alternatively, instead of a hydrothermal reduction of CO2, the redox reaction to form CH4 could have been run from H2S --> SO2. Both H2S and SO2 were detected.

I am wondering if CH4 or CO was detected in the gas stream evolved from the oven. Either would lend strong support to this hypothesis.
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here.
Invision Power Board © 2001-2018 Invision Power Services, Inc.