Peroxides? Options

[dvandorn]

We all know that the most common theories to explain the Viking wet chemistry results depend on a high peroxide content in the soils, both in the mid-latitudes (Chryse) and northern latitudes (Utopia).

As I understand it, Phoenix will be able to identify peroxides in the soil and directly test this keystone to the current interpretation of the Viking results.

So... what happens if we find little to no peroxide content in these soils?

Do we just assume that these soils are fundamentally different from the Viking soils? If so, what model predicts this?

Or do we actually begin to re-evaluate the Viking results?

What do y'all think?

-the other Doug

[tasp]

Tough call there.

My recollection is there is an abundant energy source on Mars to explain the formation of the peroxides (the high solar UV flux), the lack of organic compounds found in the soil is explained (all the carbon compounds get zapped into CO2 by the peroxides) and the interaction with the water used by Viking mimicked a chemical reaction rate that was limited by the postulated peroxide reactants, rather than by a possibly bio reaction that might have had a different rate due to 'growth' of the presumed organisms.

We have been thinking about peroxides for quite a while because their existence does a pretty good job of 'splainin what Viking found.

No peroxides would imply something even more exotic, interesting, and perhaps (bwa, ha, ha, ha) alien.

[tasp]

Just thought of this:

Would solar UV interact with the abundant chlorides in the soil to make a chlorine analog to ozone? I have precious little chemistry background so if the idea is silly, no problemo. But it seems like a chlorine version of ozone would be a pretty nasty thing to have laying around.

As I recall, the chlorides found by the rovers were quite copious . . . .

[TheChemist]

Unfortunately, as far as I know, halogens do not have any allotropes.

[PFK]

Is the argument that actual hydrogen peroxide would be there? If so, then what does the amounts that could be involved do to water properties (given that, for example, Aldrich suggests a 35% H2O2 solution in water melts at -40C)? Obviously there'd be nothing like that amount, but even so...

[dburt]

...No peroxides would imply something even more exotic, interesting, and perhaps (bwa, ha, ha, ha) alien.

Not necessarily all that alien. I'm not a chemist, but I just now looked in several freshman chemistry books. Strongly oxidizing conditions, promoted by UV or cosmic radiation, might actually produce a variety of species or surfactants, especially under extremely dry and cold conditions. Peroxide, best known (for its bleaching properties on hair) as its hydrogen compound H2O2 is one (CaO2 is also possible); superoxide, which might combine with H to form HO2 (KO2 is better known), is another, not quite as strongly oxidizing. Given the presumed high sulfate content of the soils, you might get oxidizing, acid molecules such as peroxysulfuric acid, H2SO5 or peroxydisulfuric acid, H2S2O8, or their salts. Ozone, O3, has been mentioned. Another possibility, which I've described in several talks and a paper, would be to oxidize by driving off hydrogen gas from hydroxides, yielding species such as oxy-clays or oxy-amphiboles. A likely possibility is that you might not be talking about identifiable molecules or species at all, but about unsatisfied valences on crystal surfaces, caused by UV damage that knocked electrons away from oxide ions. So failure to identify peroxide molecules as such might not require a complete trip back to the drawing board. Albert Yen of JPL has done many interesting lab experiments related to this topic, but the surface of Mars provides a natural laboratory for processes that might be difficult to duplicate in the lab.

-- HDP Don

[Juramike]

Carbonate radical [-CO3] has also been proposed as one of the eventual oxidants in a cascade:

Here is one possible sequence, starting with UV radiation pinging a nitrate anion to form peroxynitrate as the start of the cascade:
http://www.marslab.dk/ResearchSurfaceChemistry.htm

-Mike

[ngunn]

oxy-clays or oxy-amphiboles.

Hey this is getting really interesting! You mention loads of possibilities there. Could any of these materials be damp or sticky (or otherwise clingy) under the ambient conditions? I had been wondering about salty hydrated clays myself as possible culprits for the clumping. Now, if they could do that AND funny tricks with oxygen as well, this would begin to smell like a 'warm' scent to me. One of the things I'm always on the lookout for on Mars is Cairns-Smith style evolved clays - clays that have learned tricks . . . like staying damp over a surprising range of conditions and manipulating other chemical species. Could this be what Viking and Phoenix have both found? Some research needed here on what Cairns-Smith (and 'followers') said about the VIking results, if anything.

EDIT: Yes, they were onto it.

[Littlebit]

Good topic!

Another aspect to consider is the fine particle size. Many common minerals behave quite differently when they have a very large surface area; and with a non-oxidizing atmosphere, weak chemical bonding may occur that we haven't even realized.

[dvandorn]

Good topic!

Danke. In fact, in starting it, I was thinking -- now that we're within days (or weeks at most) from finding out what TEGA and the wet chemistry rigs will find on the subject, it's our last chance to speculate in absence of solid fact.

I find it useful to recap best current theory just before acquiring new empirical data, especially when it's data that we've not been able to collect before...

-the other Doug