Author Topic: Has Curiosity detected methane on Mars?  (Read 38131 times)

Online Blackstar

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Re: Has Curiosity detected methane on Mars?
« Reply #20 on: 10/26/2012 05:36 pm »

I trust it was sterile methane.  It was not seen fit to flush that system and maybe fill it with helium or some other inert gas before leaving Earth?

What do mean by "sterile methane"? CH4 is CH4
Also, even if you flush a system with an inert gas, trace molecules of CH4, etc. can rest because of adsorption, absorption and migration onto/into the material surfaces. In a vacuum environment, they then outgas and can be observed with a sensitive detector.

John has a default assumption that most of the people who work in the space field are incompetent.

Offline JohnFornaro

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Re: Has Curiosity detected methane on Mars?
« Reply #21 on: 10/26/2012 05:47 pm »
John has a default assumption that most of the people who work in the space field are incompetent.

No, John does not. 

Tell us why the yet to be purged methane in the system is known not to be contaminated by Earthly bacteria in trace amounts.

Tell us why flushing that system and filling it with an inert gas while on Earth is an "incompetent" suggestion, and not at all necessary when sterilizing the rover here on Earth.

I will admit that the phrasing of my question could have been less "loaded", and will work on that wording in the future. 
« Last Edit: 10/27/2012 01:38 pm by JohnFornaro »
Sometimes I just flat out don't get it.

Offline fthurber

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Re: Has Curiosity detected methane on Mars?
« Reply #22 on: 10/26/2012 08:00 pm »
Thanks.
I was under the impression that this would be a bit more ambiguous for Mars since we don't have a baseline of geologically produced CH4 to compare any detected biologically produced CH4 to.

Is there really a specific relative 13C abundance above which we can safely say "this has to be produced by life"?

Edit: I see your edit now.

Ambiguous yes, but intriguing. 

I think that a guess on baseline abiotic methane C13/C12 ratios could be made from C13/C12 ratios in, say, asteroids, comets, etc.  Did the Phoenix lander measure C13/C12 ratios in CO2?  That might help.

If C12 is enhanced compared to C13 above these levels then this hints at a biological origin, but we do not know if potential life on Mars is as selective as life on Earth as far as C12 uptake.  Anything more would seem very speculative.



Offline fthurber

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Re: Has Curiosity detected methane on Mars?
« Reply #23 on: 10/26/2012 08:22 pm »
It would appear that SAM's Quadrupole Mass Spectrometer is taking a measurement of the Martian atmosphere on Sol 78.  Is it looking for other gases?

Offline Quindar Beep

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Re: Has Curiosity detected methane on Mars?
« Reply #24 on: 10/26/2012 08:29 pm »
If C12 is enhanced compared to C13 above these levels then this hints at a biological origin, but we do not know if potential life on Mars is as selective as life on Earth as far as C12 uptake.  Anything more would seem very speculative.


Note incidentally that when talking methane it's 13C:14C that we're interested in. 12C is the more common marker, but it's used in different contexts.

Putting that aside as a typo, I think you've got it backwards. If 13C is enhanced it would be a strong sign of life, as there's no known abiological process that can sort between different isotopes of carbon.

Rather, if the ratio looks normal it would not rule out Martian life because Martian life may not be as selective as ours.

(On the other hand, even very simple life forms on Earth are so it would be somewhat suggestive that Mars is dead.)
« Last Edit: 10/26/2012 08:30 pm by Quindar Beep »

Offline Star One

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Re: Has Curiosity detected methane on Mars?
« Reply #25 on: 10/27/2012 12:40 pm »
Hopefully not too off topic but when MAVEN arrives at Mars is its studies of the atmosphere specifically designed to tie in with Curiosity's on the surface or is it more doing its own thing? (Probably not explained that very well.)

Online meekGee

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Re: Has Curiosity detected methane on Mars?
« Reply #26 on: 10/27/2012 06:15 pm »
If C12 is enhanced compared to C13 above these levels then this hints at a biological origin, but we do not know if potential life on Mars is as selective as life on Earth as far as C12 uptake.  Anything more would seem very speculative.


Note incidentally that when talking methane it's 13C:14C that we're interested in. 12C is the more common marker, but it's used in different contexts.

Putting that aside as a typo, I think you've got it backwards. If 13C is enhanced it would be a strong sign of life, as there's no known abiological process that can sort between different isotopes of carbon.

Rather, if the ratio looks normal it would not rule out Martian life because Martian life may not be as selective as ours.

(On the other hand, even very simple life forms on Earth are so it would be somewhat suggestive that Mars is dead.)


Do you know btw how life sorts out isotopes?   I mean in chemistry isotopes are not distinguishable.  There's clearly a density difference, but this only shows up if you ave a vertical buoyancy-based separator - shouldn't make a difference within the context of a chemical reaction.

Just curious about the mechanism here.
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Offline fthurber

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Re: Has Curiosity detected methane on Mars?
« Reply #27 on: 10/27/2012 08:14 pm »
If C12 is enhanced compared to C13 above these levels then this hints at a biological origin, but we do not know if potential life on Mars is as selective as life on Earth as far as C12 uptake.  Anything more would seem very speculative.


Note incidentally that when talking methane it's 13C:14C that we're interested in. 12C is the more common marker, but it's used in different contexts.

Putting that aside as a typo, I think you've got it backwards. If 13C is enhanced it would be a strong sign of life, as there's no known abiological process that can sort between different isotopes of carbon.

Rather, if the ratio looks normal it would not rule out Martian life because Martian life may not be as selective as ours.

(On the other hand, even very simple life forms on Earth are so it would be somewhat suggestive that Mars is dead.)


Are you sure about this Quindar?  I seem to remember that TLS is specifically designed to measure carbon-12 to carbon-13 isotopic ratios in methane not carbon-14.  As far as I know terrestrial plant life will preferentially use C12 versus C13.heck

Check out this official SAM document by Mahaffy (http://msl-scicorner.jpl.nasa.gov/Instruments/SAM/); TLS is geared toward C13/C12 measurements (and oxygen isotopes) in methane and other organics but not toward C14.   C14 is used on Earth for carbon dating but it is not very relevant on Mars...
on 14


« Last Edit: 10/28/2012 12:10 am by fthurber »

Offline Quindar Beep

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Re: Has Curiosity detected methane on Mars?
« Reply #28 on: 10/27/2012 11:58 pm »
Are you sure about this Quindar?  I seem to remember that TLS is specifically designed to measure carbon-12 to carbon-13 isotopic ratios in methane not carbon-14.  As far as I know terrestrial plant life will preferentially use C12 versus C13.

You're quite right, my mistake. The number we're after is called δ13C, which I had in my head as being the ratio of 13 to 14. But it is 12 to 13 after all:

https://en.wikipedia.org/wiki/%CE%9413C

In particular, the test we're looking at is based on the facts in the section labelled "What affects δ13C?"

Offline Quindar Beep

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Re: Has Curiosity detected methane on Mars?
« Reply #29 on: 10/28/2012 12:16 am »
Do you know btw how life sorts out isotopes?   I mean in chemistry isotopes are not distinguishable.  There's clearly a density difference, but this only shows up if you ave a vertical buoyancy-based separator - shouldn't make a difference within the context of a chemical reaction.

It's photosynthesis that does it particularly -- animals have skewed carbon isotope ratios solely because they eat plants or eat other animals that have eaten plants. The heavier isotope forms slightly stronger bonds, so plants can get more carbon from CO2 with less energy if the C in the gas molecule is 12C.

I'm given to understand that the most important chemical step in photosynthesis that causes this is the initial carboxylation, when the CO2 is attached to 1,5-bisphosphate carboxylase (https://en.wikipedia.org/wiki/RuBisCO).

The mass difference does come into play as well when you consider that a lot of the movement in plants is caused by osmosis and diffusion. Diffusion was the key to the first important separation technique used to pull apart U-235 and U-238, for example.
« Last Edit: 10/28/2012 12:21 am by Quindar Beep »

Offline KelvinZero

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Re: Has Curiosity detected methane on Mars?
« Reply #30 on: 10/28/2012 12:18 am »

Do you know btw how life sorts out isotopes?   I mean in chemistry isotopes are not distinguishable.  There's clearly a density difference, but this only shows up if you ave a vertical buoyancy-based separator - shouldn't make a difference within the context of a chemical reaction.

Just curious about the mechanism here.

(beep entered their answer as I was editing this..)

This is just a guess from some googling, but might be this: "kinetic isotope effect".. apparently heavier isotopes react a bit slower, biasing life towards lighter isotopes.

link on kinetic isotope effect:
http://en.wikipedia.org/wiki/Isotope#Chemical_and_molecular_properties

link saying biochemical reactions favor lighter isotopes:
http://arstechnica.com/science/2012/05/methane-made-from-meteors-may-explain-mars-mystery/
Our solar system has an average ratio of the two common carbon isotopes, but life tends to change that, since biochemical reactions slightly favor the use of lighter isotopes.

I imagine this bias could be exaggerated if you are performing reactions repeatedly and discarding leftovers, selecting for faster reacting carbon.

Offline Robert Thompson

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Re: Has Curiosity detected methane on Mars?
« Reply #31 on: 10/28/2012 01:17 am »
The heavier isotope forms slightly stronger bonds
Like gravitational potential of a single neutron slightly stronger?

Offline Quindar Beep

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Re: Has Curiosity detected methane on Mars?
« Reply #32 on: 10/28/2012 01:24 am »
Like gravitational potential of a single neutron slightly stronger?

No, gravity would be beyond tiny at that level. The extra neutron would mean more van der Waals forces, I think. Not a lot, but a lot bigger than gravity, that's for sure.

Offline go4mars

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Re: Has Curiosity detected methane on Mars?
« Reply #33 on: 10/28/2012 01:33 am »
It's photosynthesis that does it particularly
Just did a bit of searching to see whether ratios were skewed among chemosynthetic communities.  Didn't see enough data points to comment.  Anyone out there familiar with the C12/C13 ratios of chemosynthetic organisms (or shells of things that feed on them)?
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Offline randomly

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Re: Has Curiosity detected methane on Mars?
« Reply #34 on: 10/28/2012 01:34 am »
I think Van der waals forces are forces between dipoles , permanent or induced. How is an uncharged neutron going to affect that? Does in increase the dipole moment? and how?

Offline Warren Platts

Re: Has Curiosity detected methane on Mars?
« Reply #35 on: 10/28/2012 01:51 am »
Bottom line: The results are and will remain inconclusive--but ever-so tantalizing....

:o
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Offline Quindar Beep

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Re: Has Curiosity detected methane on Mars?
« Reply #36 on: 10/28/2012 01:59 am »
I think Van der waals forces are forces between dipoles , permanent or induced. How is an uncharged neutron going to affect that? Does in increase the dipole moment? and how?

If it were just an atom of carbon, none at all. But it's in a methane molecule (edit to add: or carbon dioxide) so it's going to change the molecular geometry a bit if you make the carbon more massive.

Not a lot, mind you, but certainly bigger than the increase in gravity caused by adding an extra neutron.
« Last Edit: 10/28/2012 01:01 am by Quindar Beep »

Offline Tetrakis

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Re: Has Curiosity detected methane on Mars?
« Reply #37 on: 10/28/2012 03:13 am »
Hello, I'm a chemist who lurks the forum.

The kinetic isotope effect in biochemistry is most frequently caused by one of two mechanisms: the lowering of the zero-point vibrational state's energy in a chemical intermediate and the increased ability for an atom (practically speaking, lighter elements like hydrogen) to tunnel through a reaction barrier. Lighter elements have a reduced ability to tunnel through finite potentials because of the inverse mass dependence in the Schrodinger equation; this is why electron tunneling is so easy as to find technological applications in electrical engineering, but proton tunneling is just an arcane curiosity of analytical chemistry used to purify deuterium.

To give a quick example of how the bond length in isotopically substituted molecules remain the same but the effective bond strength can change, consider dihydrogen cation. The morse potential for the molecule is defined by the relation between the coulombic potential energy between the two nuclei and the single electron and the kinetic energy of the electron wavefunction across varying internuclear radii, so the energy optimized bond length is not affected by the mass of either nucleon (nucleii are so heavy as to have negligible size on a molecular scale). However, the quantized vibrational energy levels are affected because the vibrational frequency of a harmonic oscillator is determined by it's effective mass; the lowest energy level is stabilized, while the highest energy level corresponding to complete bond dissociation is not. The energy difference between the resting state of the molecule and it's dissociation product is increased, increasing the effective strength of the bond (D0) while not actually affecting the potential energy surface of the system or the maximum well depth of the oscillating molecule(De).



Curiously, while the geometry of a fully energy optimized molecule at equilibrium bond length is not changed the effective bond length can be increased with lower substituted atom mass. The effective radius is altered because internuclear vibrational potentials are not perfectly harmonic, and as the lowest vibrational energy level is destabilized up the morse potential the average position of an isotopically substituted atom away from it's vibrational partner(s) is increased. This means that the effective bond length increases with decreasing mass; as an example, carbon 13 methane would have somewhat shortened C-H bonds because the effective mass of a normal mode in CH4 would be increased; the molecule would be "smaller", even though no change in the potential energy surface had taken place. Someone above said that C13 would give methane a different net dipole, or change it's van der waals forces; that would simply not be the case, due to the Td symmetry of the methane molecule. A single deuteron would, however, because the molecule would no longer have a cubic point group.

Also: Space is cool.  8)
« Last Edit: 10/28/2012 03:31 am by Tetrakis »

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Re: Has Curiosity detected methane on Mars?
« Reply #38 on: 10/28/2012 05:23 am »
Also: Space is cool.  8)

Excellent post. Thanks for de-lurking!
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Online meekGee

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Re: Has Curiosity detected methane on Mars?
« Reply #39 on: 10/28/2012 07:34 am »
Thanks for the explanations - I always wondered about that.

The chain of reasoning so far went as follows:
- Methane was detected
- Methane has a short half-life due to UV
- Methane is therefore produced
- Let's find out if it is biological in origin or not by using isotope ratios.

What is the reference point for the isotope ratio?  CO2?  Carbon in the ground?

I'm asking, since even though CO2 is not necessarily currently produced, some of it might still have a recent origin. Can we learn something from the isotope ratio of Carbon in the atmospheric CO2?
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