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

[jmknapp]

The headlines just say "finds water," but if you read the articles they discuss the findings of the D/H isotope ratios in said water and what that implies for the timeline of water loss from Mars in the Hesperian period, which was the subject one of the two recent Science articles, and is new and exciting. "The imprint of atmospheric evolution in the D/H of Hesperian clay minerals on Mars" didn't really read.

As for the recent "definitive" announcement of Martian organics:

NASA Goddard Instrument Makes First Detection of Organic Matter on Mars
December 16, 2014

The team responsible for the Sample Analysis at Mars (SAM) instrument suite on NASA's Curiosity rover has made the first definitive detection of organic molecules at Mars. ...

As part of Curiosity's plan for exploration, an important strategic goal was to sample rocks that represent different combinations of the variables thought to control organic preservation. "The SAM and Mars Science Laboratory teams have worked very hard to achieve this result," said John Grotzinger of Caltech, Mars Science Laboratory's Project Scientist. "Only by drilling additional rock samples in different locations, and representing different geologic histories were we able to tease out this result. At the time we first saw evidence of these organic molecules in the Cumberland sample it was uncertain if they were derived from Mars, however, additional drilling has not produced the same compounds as might be predicted for contamination, indicating that the carbon in the detected organic molecules is very likely of Martian origin."

[Gerald]

As you indicate, there are worlds between some detector signal of chlorinated hydrocarbons and definitive detection of chlorinated hydrocarbons derived from organic compounds of Martian origin.

With respect to D/H: The presence of liquid surface water with 3-fold enriched deuterium in the Hesperian could mean much larger amounts of water in the Noachian, at least if the D/H ratio of Standard Mean Ocean Water is assumed for the initial D/H ratio.
This makes a much denser atmosphere on early Mars more likely, too.

Thinking at methane: Methane is a much more efficient (about 30x according to some sources) geenhouse gas than CO2. If high methane abundance is assumed for early Mars, maybe the temperature dilemma can be resolved.

[jmknapp]

It's not as simple as saying that CH₄ is X times as efficient as CO₂ as a greenhouse gas. It's 38 times as efficient or whatever at the current relative concentrations in Earth's atmosphere. The effect of each gas on equilibrium temperature is logarithmic with their respective concentrations, so since CH₄ is much less abundant, increasing it has a bigger effect, molecule for molecule (the absorption properties of the two molecules do not overlap significantly so their effects add independently). But comparing two atmospheres of pure CH₄ and pure CO₂ at any given molar concentration, CO₂ wins as a greenhouse gas by far. And if CH₄ dominated CO₂ in concentration, then CO₂ would be the stronger greenhouse gas, molecule for molecule. (see: Pierrehumbert, Principles of Planetary Climate, sect, 4.5.4)

[Gerald]

So for an assumed water ocean, there should exist - within a certain temperature range - two solutions for a CO₂ / CH₄ atmospheric mix to result in a given mean temperature.
The idea seems to be not quite new, here a paper/abstract of 1993.
Whereas this paper tries to discuss away the role of methane as a greenhouse gas in the early Martian atmosphere.

[jmknapp]

To a first order, wouldn't it be a family of solutions, i.e., if you plotted the carbon dioxide vs. methane concentration to get a certain temperature given other assumptions, you'd get a curve?

The papers you link to are interesting as they give a hint at the conundrum brought up by the notion of a warm early Mars and the efforts over the years to resolve it in terms of radiative models, not altogether successfully. To higher orders there are all kinds of other factors, such as that carbon dioxide can condense, that methane is broken down by UV, that the effect of clouds is a big variable, and that average surface albedo is unknown, to name several. My impression from the recent methane results is that the main interest isn't in the atmospheric effects but rather whether it's the result of biogenesis, some other process, or perhaps some kind of as yet unidentified analytical problem. The mind-blowing thing about it is that taken at face value the episodic nature of it implies some kind of active process happening on Mars right now. Since that's an extraordinary result the team said in the supplementary materials that they have to hold out the possibility that it's an analytical error, but they investigated many such possibilities and were unable to find any such problem or alternative explanation (e.g., that the rover crushed some rocks in that area that released methane, etc. etc.).

PS Since they said the source was likely north of the short stretch where they observed the increased methane, I did a quick look at the images north of those sites. Here's a feature about due north:



The vent?

[Gerald]

With the CO₂ / CH₄ mix I've thought at the simplest-most set of scenarios, constant pressure, and a given mean temperature.
If the mean temperature is proportional to the logarithm of the abundance, we should get essentially something of the type
ln(1 + x) + ln(1 + (1 - x)) for x in [0;1],
for the mean temperature, in the most simple case, yielding one local maximum, hence two intersecting points with a horizontal line (the given mean temperature), as long as we stay below the maximum.
But of course, as we add further factors, things get so complex, that I'm not really surprised, that there isn't known a convincing solution.

If the measured methane is at least partially a result of serpentinization (the "olivine + water + carbonic acid -> serpentine + magnetite + methane" - version), this process might have been much more intense on early Mars, hence could have possibly contributed to the warming by the greenhouse effect.
Partial oxidation of methane back to CO₂ would have provided the mix for a combined absorption of sunlight.

Whether serpentinization or not, the surmised underlying methane-producing process could have been similar over billions of years, just slowed down by now, or today's presumed methane is a remnant of ancient methane production.

... Just an attempt to reduce observations to a small set of causes, well knowing that nature doesn't necessarily care about simplicity.

[Doug M.]

Mars magmas were apparently enriched in chlorine, and would have supplied hydrochloric acid to the atmosphere. It is worth noting that there is a very rich chemistry of organic molecules which contain chlorine.

Is there a cite for Martian magmas being enriched in chlorine?

Certainly there seems to be plenty of chlorine around at the surface. What's different from Earth is that while almost all chlorine on Earth is in the form of the chloride ion, on Mars we seem to be finding it both as chlorides and perchlorates. This implies a mechanism for oxidizing the former into the latter. (I've found one paper that seriously suggests static electricity from dust.) Perchlorates tend to react readily with organic molecules to produce chlorohydrocarbons, so the discovery of CHCs is consistent with a perchlorate-rich Mars.



Doug M.

[Doug M.]

Is there a cite for Martian magmas being enriched in chlorine?

Never mind -- just googling "martian magma chlorine" turns up several. So, interesting!

-- Noted in passing: there are Earth microbes that can respirate perchlorate, using an enzyme called perchlorate reductase. Perchlorate is so high up the redox chain that this actually results in oxygen as a byproduct of respiration.


Doug M.

[jmknapp]

With the CO₂ / CH₄ mix I've thought at the simplest-most set of scenarios, constant pressure, and a given mean temperature.

OK, if you hold the pressure constant, temperature will be at a maximum for a certain CH₄/CO₂ ratio and for equilibrium temperature below that (but not too much lower) there will be two solutions as you say. The maximum will be very broad and flat except at the extremes, so the two solutions would be on the high CH₄, high CO₂ ends in general.

[TheAnt]

-- Noted in passing: there are Earth microbes that can respirate perchlorate, using an enzyme called perchlorate reductase. Perchlorate is so high up the redox chain that this actually results in oxygen as a byproduct of respiration.

Correct, that's why the Phoenix result was considered to be that interesting.

As for the methane, we should not read too much into this measurement, the manner in which the level did go up do tell us one thing: It might have come from a relatively nearby location and probably from the subsurface of Mars.

[Gerald]

OK, if you hold the pressure constant, temperature will be at a maximum for a certain CH₄/CO₂ ratio and for equilibrium temperature below that (but not too much lower) there will be two solutions as you say. The maximum will be very broad and flat except at the extremes, so the two solutions would be on the high CH₄, high CO₂ ends in general.

The rather flat maximum is a good point. It makes the radiative forcing of a CH4 / CO2 mix rather stable within a wide range of mixing ratios.
On the other hand it makes radiative forcing very sensitive to trace species.
In the context of an apparent contradiction of Kite's snowball model with a warm and wet early Mars (if one tries to avoid a highly variable climate), this makes me rethinking the SAM measurements of chlorinated hydrocarbons.
Perchlorates are thought to form photochemically in the atmosphere. But once chlorine is in the atmosphere, shouldn't we get a rich chlorine-organic photochemistry in the presence of methane? (Actually it's long-known.)
Complex chlorine-organic molecules once formed, should precipitate due to their higher boiling point, and become part of the sediments.
So couldn't either some of the found chlorinated hydrocarbons be taken literally, or, if the chlorine components are interpreted as a reaction product with perchlorates, these perchlorates partially be decay products of chlorinated hydrocarbons formerly in the Martian atmosphere?
The lack of a clear perchlorate signal (in contrast to halite) in CheMin data thus far - although exlainable by low abundance or amorphous modifications -, has also inspired me to think about alternative approaches.

Radiative forcing is known to be very sensitive to chlorinated hydrocarbons, at least on Earth, see e.g. table 2.3., on page 53 of this paper.
Therefore the vague idea, that some of the possible inconsistencies could (or even should better) be resolved via adding chlorinated hydrocarbons to the (photochemical and climatic) models of early Martian atmosphere.

This FORTRAN software for climatic simulations (mainly of Earth) has been used in this paper.
It considers overlapping absorption lines, inner-atmospheric radiation exchange, and includes several trace species.
Not quite sure, to which degree the sw and the paper are applicable to Mars, but the underlying physics should be similar, at least.

[ChrisC]

Just a heads up, the Discovery Channel is airing a documentary tomorrow at 10pm EST called "Red Planet Rover" featuring the new findings. https://www.youtube.com/watch?v=TOhBDy4e_ec

Does anyone know if this show is being repeated? I found out about it too late to set the DVR. I scoured the Discovery website (and the web in general) looking for rerun info, found nothing. I also asked them via Facebook, and will relay here if they reply. Surely they will rerun at some point ...

[jmknapp]

It'll be interesting to see any results from India's orbiter with the Methane Sensor for Mars (MSM) instrument that's designed to measure methane down to the surface over a long period of time with "several ppb" accuracy. Haven't heard anything yet though.

[Mr Valiant]

Any chance the Methane spike may be due to interaction from Comet C/2013 A1 (Siding Spring)?
Shame the isotope ratio is out of range as we could've compared it to results from Rosetta.

[Hungry4info]

From: http://www.fromquarkstoquasars.com/curiosi...-spike-on-mars/

Curiosity was able to detect two significant spikes of methane, one in late 2013 and once in early 2014

Siding Spring flew past Mars on 19 Oct 2014.

Something tells me the two are unrelated.