MSL - SAM and CHEMIN, Discussion of the science/results from these instruments Options

[djellison]

I think we're looking at a work in progress with the SAM results.

Errr - obviously. They said as much yesterday.

[serpens]

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]

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]

...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.

[mcaplinger]

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 don't think so. At the time H2O2 or superoxides were used as explanations for the O2 release seen after wetting in the GEx experiment, and CO2 release in the LR experiment. I'm no chemist but I don't think perchlorates alone explain these results; see http://www.lpi.usra.edu/meetings/lpsc2011/pdf/2003.pdf for example. And I don't think that perchlorates are technically superoxides.

I'd be happy to be proved wrong but it would take an actual reference from pre-Phoenix to convince me that anyone had mentioned perchlorates in the context of Viking.

[NickF]

And I don't think that perchlorates are technically superoxides.

You'd be correct to think this. Perchlorates are undoubtedly good oxidants (although there are kinetic barriers to their activity due to steric hindrance of the central chlorine atom), but they are not superoxides. Perchlorates can undergo autoxidation to form superoxide in the presence of O2.

[mcaplinger]

...it would take an actual reference from pre-Phoenix to convince me that anyone had mentioned perchlorates in the context of Viking.

For example, Zent and McKay's 1994 Icarus paper "The Chemical Reactivity of the Martian Soil and Implications for Future Missions" http://www.sciencedirect.com/science/artic...019103584710475 says nothing about perchlorates that I can see.

[marsophile]

One thing that seems puzzling is why chloromethanes were not detected by the TEGA instrument on Mars Phoenix. These two papers, proposing reactions with calcite and nickel, respectively, provide possible answers:

https://docs.google.com/viewer?a=v&q=ca...m5mP8BGPFzw7JXA

https://docs.google.com/viewer?a=v&q=ca...OC2KmIlYeHNnaWA

[Don1]

Elements like potassium and sodium have several different oxides. There is the oxide, the peroxide, and the superoxide. Potassium superoxide (KO2) was suggested to explain the results form Viking.

Hydrogen peroxide (H2O2) was also suggested to explain the Viking results.

Unrelated to superoxides, there is a whole family of oxy-chlorine ions, going by the names of hypochlorite, chlorite, chlorate and perchlorate. They feature from one to four oxgen atoms bonded to each chlorine. Perchlorate has four oxygens. Perchlorates on Mars never got much attention before Phoenix.

The non-detection of chlorine containing species by Phoenix requires an explanation. The paper linked above says that chlorine will react with the nickel which the oven was made of.

[stone]

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

I looked for an article on perchlorates on mars prior to the 1990s and I cold not find anything, do you have a hint were to look?

There are only two mentioning mars and perchlorates at all.

http://dx.doi.org/10.1016/0019-1035(78)90052-0
http://dx.doi.org/10.1016/0019-1035(81)90041-5

Thanks

[mcaplinger]

I looked for an article on perchlorates on mars prior to the 1990s and I cold not find anything, do you have a hint were to look?

I don't believe there are any, see post #51 and following.

[stone]

ADMIN TIP: When replying to a post immediately preceeding yours, use the "Add Reply" or 'Fast Reply" button and not the "Reply" button.

This is what I thought.

The perchlorates make it very difficult to get good data from the SAM instrument. The chlorine and oxygen generated at temperatures above 250°C have a very destructive influence on most of the organic material.
I hope that the perchlorates are concentrated in the dust and that the rocks had no mechanism to get soaked up with the perchlorates.

[Gerald]

For the 44th Lunar and Planetary Science Conference (2013) the abstract POSSIBLE DETECTION OF PERCHLORATES BY EVOLVED GAS ANALYSIS OF ROCKNEST SOILS: GLOBAL IMPLICATIONS is already available. Old Viking results are also discussed.

[stone]

With the Viking data showing chlorohydrocarbons and looking back it looks very much like a part of this was created by the same mechanism observed in the SAM instrument. This makes it look like there was perchlorate at the two Viking landing sites on the one for Phoenix and at MSL. So the perchlorates are everywhere. The Biemann Navarro-Gonzales dispute on the Viking results may go into the second round.