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

[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 + MO_n + heat --> H2 + CH4 + CO + MO_n+2
MO_n+2 + heat --> MO_n + 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]

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]

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]

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...

[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.