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Thread: Spontaneous Hydrogen Peroxide generation to etch some dark slope streaks on Mars.

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  1. #1
    Join Date
    Mar 2008

    Spontaneous Hydrogen Peroxide generation to etch some dark slope streaks on Mars.

    A discovery paper today from PNAS:
    Spontaneous generation of hydrogen peroxide from aqueous microdroplets
    Abstract only:

    The majority of dark slope streaks on Mars are dry cascades of dust. A few seem to last beyond global dust storms. They tend to show no relief but may brighten with age and show some small relief after completely fading.

    A possibility is that a subset of streaks might be due to etching from a gas leaked from the apex where rock has been exposed, If the candidate gas was released water vapor from exposed subsurface, this new paper suggests that H2O2 can form without catalysts. As microdroplets get smaller, the process gets more efficient. New slope streaks appear during MRO surveys but so far none have been witnessed in the forming stage. An important constraint on Mars is that as the sun rises H2O2 is quickly destroyed. This may imply that formation may be before dawn making it hard to observe. If the etching produces heat,orbiting infrared sensors might see it. Length of streak might depend on water vapor volume, slope angle steepness, and how long before sunlight comes.

  2. #2
    Join Date
    Jun 2002
    H2O2 is not much denser than CO2, the main component of mars' atmosphere. That being the case, I'd expect to see feathery looking streaks, driven by wind, not the straightish to meandering dark areas we do observe.
    The microdroplets should be pushed around by wind.
    Looks to me like there's at least a couple different mechanisms involved.

  3. #3
    Join Date
    Mar 2008
    Streak etching for some slope streaks

    The basic idea is the transition from ferrous to ferric in the presence of H2O2. Mars is red because of completely oxidized iron. There are three forms of iron oxide with FeO being least common. The albedo due to dust reflects the overall ratio of these oxides. With H2O2 the ratio can be locally altered to a more oxidized ratio making an even darker red streak. The more concentrated the rust the less cohesive becomes the streak. This can lead to preferential erosion of the streak which leaves no albedo contrast but a perceptible relief seen in MRO images at high resolution. I refer to these as “dead” streaks. These are not to be confused with dark streaks that have been getting brighter over time. These have no albedo contrast but show a relief outline of where a dark streak used to be present.

  4. #4
    Join Date
    Mar 2008
    A couple of Schorghofer et al links

    Slope streaks on Mars: Correlations with surface properties and the potential role of water


    While the constraints regarding low thermal inertia and steep slopes is not surprising, a third constraint that the temperature needs to be above 275K at some time was surprising. This is where water triple point is suggested. No particular mechanism of how water is involved was given. Perhaps an overburdened slope only needed the boiling of water at the apex to trigger a dry dust avalanche. Perhaps water has a greater role.

    With regard to the H2O2 hypothesis, H2O2 should be hard to be present. Not only does sunlight on Mars destroy H2O2 but one of the oxides of Iron can also destroy it. So it needs to be made “on the go” before being destroyed where a reservoir would be unlikely. The paper on spontaneous generation of H2O2 may allow for a hypotheses.

    Slope streaks do not disappear at global dust storms but seem to have lifetime of 30-40 years. This will eventually need explanation.


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