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A coupled soil-atmosphere model of H2O2 on Mars
M A Bullock1, C R Stoker, C P McKay
1Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder 80309-0392, USA. ZODIAC::BULLOCK
Icarus
|January 1, 1994
Summary
The Viking missions suggested Mars soil is reactive due to oxidants like hydrogen peroxide (H2O2). Our model shows H2O2 concentration drops to zero within meters, potentially allowing protected organic compounds to exist deep in the Martian soil.
Area of Science:
- Planetary Science
- Astrobiology
- Atmospheric Chemistry
Background:
- Viking missions indicated reactive Martian soil, leading to theories of soil oxidants.
- Hydrogen peroxide (H2O2), produced photochemically, is a plausible Martian soil oxidant.
- Previous experiments suggest H2O2 could explain Viking Labeled Release results.
Purpose of the Study:
- To model the transport and distribution of hydrogen peroxide (H2O2) in Martian soil and atmosphere.
- To assess the depth of H2O2 penetration and its implications for the preservation of organic compounds.
Main Methods:
- Developed a coupled soil/atmosphere transport model for H2O2 on Mars.
- Analyzed H2O2 diffusion, adsorption, and catalytic destruction within the soil.
- Parameterized the model using the lifetime of H2O2 against heterogeneous catalytic destruction.
Main Results:
- H2O2 concentration in Martian soil reaches zero at a finite depth due to nonlinear diffusion.
- For H2O2 lifetimes up to 10^5 years, the extinction depth is less than 3 meters.
- Maximum H2O2 concentration in the top 4 cm is ~240 nmol/cm³ with lifetimes >1000 years.
Conclusions:
- Martian soil H2O2 concentration decreases with depth, creating potential refugia for organic matter.
- Significant H2O2 soil loss requires lifetimes less than a few hours; longer lifetimes decouple atmospheric and soil concentrations.
- The existence of protected organic compounds, possibly from meteorites or past life, remains plausible beneath the reactive surface layer.