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

[marsophile]

Did they specifically identify perchlorate, or is that inferred from the chlorinated hydrocarbons?
Would water percolating through rocks really deposit (very soluble) perchlorate, or wash it away?
AFAIK, rocks on Earth do not contain substantial perchlorate.

HCl was mentioned, so maybe that was the source of the chlorination? Or maybe perchlorate from some of the soil left over from Rocknest?

At least now the level of chlorinated hydrocarbons is way above the blank background.

[fredk]

All I remember is a statement that they saw perchlorate and no further details. Maybe someone else caught more?

[Don1]

They see oxygen released at a temperature consistent with perchlorate decomposition and they see the production of chlorinated hydrocarbons.

They did mention that they had tried to flush the leaked reagent out of the system by preheating the sample for 20 minutes.

[t_d]

Wouldn't heating the sample for twenty minutes drive off other interesting compounds and molecules?

[Phil Stooke]

Yes, and they measure them all.

Phil

[centsworth_II]

Here is a transcript of SAM PI Paul Mahaffy's response to a Craig Covault question (at 48:30):

"In the rocknest sample we certainly detected some vapor that was very easily identifiable. A trace amount of vapor -- nanomoles -- that's a signature of what's inside our wet chemistry cells. And so one way or another, whether it was through a very small leak through one of the pinch offs, or processing, a little bit of that vapor is there.

What we are doing is trying to get smarter about how we do experiments to avoid some ambiguity with regard to where carbon coming from our sample comes from. And so what we did with these [rocknest] samples was we preheated the sample and let helium flow over it for something like twenty minutes and [it's] a very clear signature of all that vapor being flushed out of the system. So that's really a very robust way we believe of getting around this issue that we saw at rocknest."

[elakdawalla]

I thought I heard "nanomoles," not "millimoles."

[centsworth_II]

I thought I heard "nanomoles," not "millimoles."

Right, thanks, corrected. I even had "nano" written down.

[Doug M.]

A number of articles are mentioning the presence of nitrogen and phosphorus. I listened to the entire press conference, but I didn't hear anything about either of these two elements. Sulfates and sulfides and carbonates, but nothing about nitrogen or phosphorus. Did I miss something? And if these were found, what were the concentrations, and what compounds do they think they're coming out of?


Doug M.

[orbitmars]

P2O5 has been detected in Gusev, Meridiani and Gale according to this LPSC 2013 abstract: http://www.lpi.usra.edu/meetings/lpsc2013/pdf/1653.pdf

[jmknapp]

Ken Kremer from Spaceflight magazine asked about N and P:

Kremer: I'm interested to know, maybe even from Paul Mahaffey, about the SAM run, did you see any nitrogen, or phosphorous or chlorobutanes, and can you talk about what was the weight percent level of the phyllosilicates?

Mahaffey: I think the weigh percent of the phyllosilicates is best answered by CHEMIN, and you [looking at David Blake] gave a number for that...

Blake: 20 to 30 weight percent.

Mahaffey: ..and, did we see nitrogen compounds, we certainly are in our trace gases looking for those. It seems that we have some nitogen oxides coming up, we're looking at compounds like HCN and so on. Deconvoluting those spectra requires work and so we're working away on that, but it sure looks like we have nitrogen compounds there. In terms of phosphorous, we haven't seen any, but that really is an APXS result, they see phosphorous in their compounds. Very interestingly, we see a fair bit of hydrogen chloride coming up into our lines, and so the chlorine is not just producing these trace chloromethane compounds, but is also producing hydrochloric acid.

Just before that, John Grotzinger said this about finding CO₂ in the SAM gases:

Grotzinger: That's what we're real excited about there, because then that gives us our sort of desiderata of key elements that are the building blocks for life: hydrogen, oxygen, phosphorous, sulfur and then of course nitrogen and then also carbon.

A mnemonic for that desiderata for life is sometimes given as CHNOPS (chi-nops).

[Doug M.]

So, it looks like we're seeing P2O5 at about 0.5% to 1% by weight of various rocks, which works out to around 0.2% to 0.4% phosphorus by weight. Okay.

But OTOH, it appears that nitrogen is scarce -- a trace that they have to look hard to sort out, if it's there at all. Nitrates, nitrites, cyanides or nitriles, if present at all, must be in very low concentrations, at least in the samples taken so far. Do I have this right?


Doug M.

[Doug M.]

A mnemonic for that desiderata for life is sometimes given as CHNOPS (chi-nops).

Hm, never heard that one before. Here on Earth 96%-98% of biomass is CHON. Phosphorus is the next most common, typically between 1% and 2%. Then calcium, with the exact figure a bit blurry depending on whether you count stuff like seashells as "biomass", but generally around 0.5%. (It's more like 1.5% for humans and other vertebrates, but that's because we concentrate calcium in our skeletons.) Then you have another group -- potassium, sulfur, chlorine, sodium and magnesium -- that are all between 0.5% and 0.05%; together these make up a bit less than 1% of all biomass. (They're all utterly essential, though. There's no life, not even weird extremophiles, that doesn't rely on these guys.) Sulfur is still below potassium and calcium, though. So maybe that mnemonic should be CHNOPKaCS?

After that you have a steep dropoff to the next most common element, iron, which is typically less than 0.01% of biomass. AFAIK there's no life that doesn't use iron in its chemistry, but IANA biologist and I wouldn't be shocked to find some odd microbe getting along without it. It's involved in a number of important biological processes, but it doesn't seem to be mission-critical the way that the elements listed above are. So if we're looking at the elements needed for life, they're CHON, followed by P-Ca, followed by K-S-Cl-Na-Mg and maybe Fe.


Doug M.

[NickF]

Phosphorous (in the form of phosphate) is required for nucleotide biosynthesis. Iron's pretty important for redox biochemistry too; it's essential for haem (think cytochromes) and FeS cluster assembly. I'm not aware of any organisms that don't utilise it.

[jmknapp]

Did he say how much N was found? Or does the fact that the N signals need to be "deconvolved" imply trace?