(I just had to run this death....)

At standard temperature and pressure on Earth (273 K, 101.3 kPa), 1 mol = 22.4 L

Assuming a pure N2 (m.w. = 28) atmosphere for Earth: 1 mol/22.4 L = 28 grams/22.4 L.

So air 1 ppb on Earth in 22.4 L (STP) = 28E-9 grams/28 grams (=1 part per billion)
28E-9 grams in 22.4 L = 28 nanograms/22.4 L (STP)

For methane (CH4; m.w. 16), 1 ppb corresponds to is 28E-9 g * (1 mol methane/16 g) = 1.75E-9 mol methane

1.75 E-9 mol methane/22.4 L = 0.078 nM concentration.

***

On Mars, what is a typical pressure/temperature at the surface?

Wild guesstimate/generalization: use 233 K (=-40 C), and 0.6 kPa

So pV=nRT:
For pressure: 22.4 L mol -1 x (101.3 kPa/0.6 kPa) = 3782 L mol-1 at Mars pressure
For temperature: 3782 L mol-1 x (233 K/273 K) = 3230 L mol-1 at Mars surface pressure temp.

Assuming pure CO2 (m.w. = 44) atmosphere for Mars: 1 mol/3230 L = 44 grams/3230 L

So 1 ppb at Mars surface in 22.4 L (Mars guesstimate) = 44E-9 grams/44 grams (=1 part per billion)
44E-9 grams in 3230 L (Mars guesstimate).

For methane (CH4, m.w. 16) this corresponds to 44E-9 grams * 1 mol methane/16 g = 2.75E-9 mol methane

2.75 E-9 mol methane/3230 L = 0.8 picomolar concentration. (=0.0008 nM concentration)

Put another way, 1 ppb methane on Earth has 100 times more CH4 molecules per unit volume than on Mars at my guesstimated surface temp and pressure.

(Handy data for all of you thinking about growing beans on Mars…..)

[/nerdgasm]

-Mike

...Mike, thou art an ubersciencegeek amongst geeks...thank you very much!

That truly puts this in perspective; ain't very much methane at all, and that actually makes the whole issue even more puzzling. Are there really only a (literal) handful of vents on the entire planet? I know that the crust is supposed to be very thick, but jeez...

Sloppy, Mike, sloppy ;-)

If one cares enough to worry about ppb or whatever not being kosher units, then one should
really note that the litre is a unit of capacity, rather than volume

1 mole occupies 22.4 dm^3 at STP.

As if my opinion might be important, I would have voted for such a ban, too.

When you begin to talk about PPBs, PPMs, or even simple percentages, such ratios need further definition to become useful. I normally prefer to think about mass ratios, but volume and weight ratios remind us that there are other perspectives that are useful to consider. 22.4 liters/mole at STP is one of my favorite numbers.

Interesting analysis from Kelly Beatty over on Sky & Telescope. Apparently there was water vapor associated with the emissions, and they were definitely transient. The plot thickens considerably.

Now, what's REALLY strange is why two or more locales separated by hundreds if not thousands of km seemed to pop off at nearly the same time. Not even close to enough information to make an intelligent guess as to what's going on geologically, if anything. Boy, do we need some seismometers on Mars.

Is there any chance that they were several drifting burps of the same plume?

I suppose so, but there's no way to tell. The data is at planetary-scale resolution, so it's obviously well past the originating event since the byproducts of the emission have diffused throughout most of a hemisphere.

Think I'm gonna start promoting my Mars Transient Event Detector idea again!

A sub-surface source to me is the most interesting possibility and I am happy to imagine it is the most likely explanation for the current data. But given the poor time and spacial resolution I don't think a surface process (i.e. photochemistry) is out of the question.

Cents, I was leaning towards a surface process myself, but the addition of water vapor seems to argue for a more dynamic event. Could go either way still, though; hopefully there will be more data soon.

The dynamic event could involve the water release only. Once released, the water is involved in a surface process that produces the methane. But, as I said, I'll be happy to have surface production proved wrong.

Oh, certainly; we'd all like to find a fumarole, but all possibilities need to be considered. Probably a good time to remind ourselves that Mars is an alien world, and terrestrial assumptions do not necessarily apply.

I will admit that I am considerably more excited by this discovery now than I was a couple of days ago.

I wonder what the best way to localize transient methane releases would be?

An orbital spectrometer? Or a ground network of landers with some type of 'sniffer' (GC-MS)?

Could a network of upward pointing LIDARs be used for detection of methane absorption bands? Then you'd get cloud/precip data while waiting around for the ground to burp.

check out these links:

http://futureplanets.blogspot.com/2009/01/...rs-methane.html

http://futureplanets.blogspot.com/2009/01/...rs-methane.html

http://mepag.jpl.nasa.gov/reports/MSO_SAG2...EPAG_29may1.pdf

Not trying to be a sadonecroequomasochist, here, but one request for clarification, on the "biology question," if I could.

I imagine that any future landers or orbiters which would feature biology-oriented sensors would provide allowable bases upon which discussion of those sensors and the data they collect would in fact be proper. And that, for example, any credible new interpretation of the Viking biology experiments might be allowable, but again within the strict context of the experiments themselves and the specific data returned.

Am I understanding this correctly? It seems inherent in the standing argument for the ban (with which I do agree, I'm happy not to have to see anyone here deal with the whackos).

-the other Doug

Mike, thanks for your excellent analysis. I am glad you made this point, it is a key one that we chemists should've made earlier.

Just to run another analysis to the death....

The mass of the Martian atmosphere is 2.5E16 kg http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html

Working from the APOD map http://apod.nasa.gov/apod/image/0901/marsm...ne_nasa_big.jpg
and assuming by my swag guestimate from eyeballing this map that about 20% of the martian atmosphere contains 20 ppb of methane (that looks about correct from the map),

Then there is a total of 50,000 metric tons of methane in the Martian atmosphere. So the observed 19,000 metric ton 'plume' was 38% of the total atmospheric methane.

math: = 2.5E16 * 0.2 * 20 / 1e9 /2000 = 50,000 metric tons

Thank you, and excellent, just as I expected. A photochemical process which produces methane which is catalyzed over a metal oxide dust or clays requires water. Water is the source of the hydrogen during the photoreduction of CO2. {note: Metal sulfide dusts or minerals could work too as photochemical catalysts, there are papers on this too.}

The detection of water vapor in a region of high solar irradiance are exactly the localized conditions which I was hypothesizing would be required for the photochemical mechanism to produce methane, that I proposed several years earlier over at the SDC forums, and reposted some of the arguments into a UMSF thread here: http://www.unmannedspaceflight.com/index.p...&hl=methane

{p.s. The photochemical mechanism I have proposed on SDC and then on UMSF is quite different from that later published by Bar-Nun (thank you Alex Blackwell for a copy of his paper from Icarus back then) (and whose hypothesis is disputed in a subsequent letter). Bar-Nun's mechanism was direct high energy photolysis without a catalyst. It's problem is that the light at that wavelength may be highly absorbed, and not reach the surface with much intensity.}

If I wasn't so busy with my job, which is in a very different field, I would do some research and publish a paper on this. if anyone here is qualified to pursue this, I would be happy to collaborate.

Below are a few of the score(s?) of photochemistry papers on the photoreduction of CO2 with water with shorter wavelength light (250 nm - 450 nm). Light of these ultraviolet wavelengths should reach the martian surface in significant doses. There are at least 20 journal papers on the subject of photoreduction of CO2 to produce methane, of course none having anything to do with Mars:

+++++++++

Photoreduction of carbon dioxide and water into formaldehyde and methanol on semiconductor materials. Aurian-Blajeni, B.; Halmann, M.; Manassen, J. Weizmann Inst. Sci., Rehovot, Israel. Solar Energy (1980), 25(2), 165-70. CODEN: SRENA4 ISSN: 0038-092X. Journal written in English. CAN 94:124490 AN 1981:124490 CAPLUS

Abstract

Heterogeneous photoassisted redn. of aq. CO2 to produce MeOH [67-56-1], HCHO [50-00-0], and CH4 [74-82-8] was achieved by using semiconductor powders with either high-pressure Hg lamps or sunlight. The reaction was carried out either as a gas-solid process, by passing CO2 and H2O vapor over illuminated semiconductor surfaces or as a liq.-solid reaction, by illuminating aq. suspensions of semiconductor powders through which CO2 was bubbled. Best results, under illumination by Hg lamps, were obtained with aq. suspensions of SrTiO3, WO3, and TiO2, resulting in absorbed energy conversion efficiencies of 6, 5.9, and 1.2%, resp.

++++++++

Reaction mechanism in the photoreduction of CO2 with CH4 over ZrO2. Kohno, Yoshiumi; Tanaka, Tsunehiro; Funabiki, Takuzo; Yoshida, Satohiro. Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyoto, Japan. Physical Chemistry Chemical Physics (2000), 2(22), 5302-5307. CODEN: PPCPFQ ISSN: 1463-9076. Journal written in English. CAN 134:185804 AN 2000:788525 CAPLUS

Abstract

The surface species produced during photoredn. of carbon dioxide with methane over zirconium oxide were obsd. by IR spectroscopy. One of them was a reaction intermediate and decompd. to CO at .apprx.623 K, and the other did not decompd. even at 673 K was called a carbonaceous residue. IR spectral features allowed to identify the latter as the surface acetate. Several properties of the former species were quite similar to those of the surface formate ion, which was a reaction intermediate in photoredn. of CO2 by H2 over ZrO2. The former species was assigned to the surface formate, which was also supposed to be an intermediate of photoreaction between CO2 and CH4. The existence of another carbonaceous residue different that the surface acetate was suggested. The EPR spectrum indicated the photoexcitation of adsorbed CO2 to the CO2- anion radical, and the interaction of the CO2- radical with CH4 in the dark. On the basis of these results, a possible reaction mechanism in this reaction was proposed.
+++++++
Titre du document / Document title
Photocatalytic production of methane and hydrogen through reduction of carbon dioxide with water using titania pellets
Auteur(s) / Author(s)
SENG SING TAN (1) ; ZOU Linda (2) ; HU Eric (1) ;
Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)
(1) School of Engineering and Technology, Deakin University, AUSTRALIE
(2) Institute of Sustainability and Innovation, Victoria University, AUSTRALIE

Résumé / Abstract
This paper presents an experimental study on employing a pellet form of catalyst in photo-reduction of carbon dioxide with water. Water was first absorbed into titania pellets. Highly purified carbon dioxide gas was then discharged into a reactor containing the wet pellets, which were then illuminated continuously for 65 hours using UVC lamps. Analysing the products accumulated in the reactor confirmed that methane and hydrogen were produced through photo-reduction of carbon dioxide with water. No other hydrocarbons were detected. Increasing the temperature in the reactor has showed little change on the amount of methane produced.

...an opportunity to revisit the issue as and when it happens.

In the mean time, a ban on biology is a ban on biology. Like politics and manned.... NO exceptions. These rules are made as simple as possible - to follow, and to police, so there can be no arguments or cries of foul play.

Thank you Jon Clarke on SDC forum for finding a copy of the Mumma paper preprint, which can be found here: http://images.spaceref.com/news/2009/Mumma...M_accepted2.pdf

I have read it over a couple of times, but not in deep depth on the spectroscopic data.

It seems that Mumma estimates 42,000 tons total methane in the Martian atmosphere at the height of the big 'plume', which is very close to my guestimate above.

Spatial resolution depending on how Mumma's group binned multiple measurements. Measurements were taken on the IRTF scope (3m) in Hawaii, and Keck-2. Best resolution was about 195 km, but longer time exposures and binning reduced this to about +/- 5 degrees of latitude and longitude according to the error bars on the plots, and in 30 min time up to 16x10 degrees (long/latitude) or 948x546 km. So no, this cannot really resolve a 'vent' or identify exactly a surface feature associated with the methane.

Methane was removed quite quickly from the atmosphere, and Mumma suggests that highly oxidized dust surfaces in the atmosphere are responsible. I agree.

He discusses seeps and crater faces as sources of methane.

He has a rather long speculative discussion of biological sources for methane generation.

Photochemical sources of methane are not really considered or discussed, other than a very brief dismissal.

Tomorrow I will read throught the spectrocsopic part of the paper deeper. My two quick reads saw nothing amiss, and his evidence for methane detection seems compelling.

Mumma also said during the press conference that results from other areas of Mars that are being reduced for future publication were totally verboten for discussion at this time. Quite sharp and no-follow-ups in tone.

Is he really saying that these relatively confined areas are the *only* methane plumes on Mars as a whole? If so, why such a sharp cut-off of any discussion of some other areas that have been analyzed? (Or maybe there are other things being discovered in other areas that they're trying pin down before discussing them?)

I guess I just don't see anything unique about the landforms associated with the plumes that you can't find methane-free elsewhere. Seems odd to find methane over only *some* examples of cratered terra-style surfaces but not a majority; same with areas like Nili Fossae, there are at least a few other areas that resemble it, but seem to lack methane. I think it might be difficult to pin down sources and origins of methane that seem to have little to no relation to the landforms from which the gas is being released...

-the other Doug

In this NASA You-Tube video, Mumma says they have discovered methane being released from "several discrete vents, or sites." The truth is that they have seen methane appearing in several areas on Mars. They have not at all discovered it being released from vents, or even discrete sites. He goes on to list the "two principle" possible origins of this methane as biochemistry or geochemistry. Once again photochemistry does not make the list. I wonder how seriously the scientists are taking photochemistry as a possibility and on what merits they are apparently brushing it aside.

And we wonder why the popular press can't get it right.

I'm speculating here, (and I haven't yet read the papers posted above), but to get the photochemical reduction of methane from CO2 would require a wet catalyst. The water acting as the hydrogen source. So you'd need wet (or icy) dust grains, probably airborne condensation nuclei in the clouds.

But dust grains in the atmosphere are highly oxidizing. How easy is it to do a photochemical reduction on (or in the presence of) an oxidizing surface?

At first glance, it seems kinda tough...

http://blogs.discovermagazine.com/badastro...ane-media-mess/
He points out that the press release was titled "Discovery of Methane Reveals Mars is not a Dead Planet"

Just sayin...

Agreed. I think it would require non-oxidizing metal oxide surfaces, such as the grains in clays, and water vapor (morning frosts?). But as we know, large parts of the Martian surface are coated with highly oxidized dusts (superoxides, peroxides, chlorates). We need to know which parts of the martian surface are not dusted with dusts whose surfaces is highly oxidized.

The mechanism for converting iron oxide, C02 and water into methane require heat. A theory was that some sort of leftover volcanic heat is doing the cooking, allowing the chemistry to make methane. The problem with that theory is we've never witnessed any sort of volcanic activity on Mars - only the long-dead results of volcanism remain.

So PCHEM processes are being looked at as a possible source, but there seems to be a very good chance that it's from biological processes.

And his reference about "dead planet" includes both geological as well as biological definitions. If it's not biologically "alive", it must be geologically "alive", or there wouldn't be active ongoing processes which end in methane production.

That's the geochemical method. I was proposing that released water would be available for photochemical production of methane. (The forgotten reaction)


Once again, what about photochemical production? Would that rate calling Mars "alive"?
(Of course, Mars is "alive" to many of us already, no matter what is found in the future.)

True. It sounds ambiguous, and I think it's meant to be. I've seen a 'dead' or 'geologically dead planet' (or moon) used to mean one which has no volcanism (like Mercury or our Moon).

Poking around, it might be possible to use an orbiting downward LIDAR to get localization of trace gas data.
Found this abstract:

Riris et al. AGU Abstract#P51C-212. "Mars Trace Gas Detection with a Remote-Sensing LIDAR". (Abstract here)

From the abstract:
"The small laser footprint and the resulting high spatial resolution, will also allow the identification biologically and geologically active sites for a future landing missions."

-Mike

This is an interesting idea. I wonder how much power the laser would require, in order to generate a significant enough scattering signal to be observed from orbit with good S/N? Also, what's the vertical resolution? And would this just work during the martian night, for that wavelength? (I am guessing it might work better then; but if so, it would require on some type of on board energy storage system, such as batteries)

Given the almost complete absence of impact craters on some of the Tharsis volcanoes volcanic activity certainly continued until fairly recently (geologically speaking). Here on Earth some active volcanoes have dormancy periods that run into tens of thousands of years, so the fact that we have seen no activity in a few decades is hardly conclusive.