Frost-weathering on Mars: experimental evidence for peroxide formation

Area of Science:

• Planetary Science and Astrobiology
• Geochemistry and Mineralogy

Background:

• The Viking lander experiments on Mars detected unexpected chemical activity in the soil.
• Previous studies have explored potential chemical reactions that could occur on the Martian surface.

Purpose of the Study:

• To investigate the interaction of water frost with common Martian minerals (olivine and pyroxene) under simulated Martian conditions.
• To determine if these interactions could produce oxidants similar to those detected by the Viking landers.

Main Methods:

• Laboratory experiments exposing olivine and pyroxene samples to H2O frost at temperatures between -11°C and -22°C.
• Analysis of reaction products, including gas evolution (O2, CO2) and pH changes upon exposure to liquid water and formate solutions.
• Proposed a chemical model involving mineral reduction and peroxide formation.

Main Results:

• An acidic oxidant was produced when H2O frost interacted with olivine and pyroxene.
• Exposure to liquid water released significant amounts of oxygen gas (O2).
• Formate oxidation to carbon dioxide (CO2) was observed, consistent with Viking Lander results.

Conclusions:

• Chemisorbed hydrogen peroxide is a plausible byproduct of mineral-frost interactions and may explain the Viking Lander's findings.
• This mechanism requires only a small percentage of frost-weathered material in Martian soil.
• The proposed model aligns with the observed stability and decay characteristics of Viking soil oxidants.