Completion of the Viking labeled release experiment on Mars

Area of Science:

• Astrobiology
• Planetary Science
• Geochemistry

Background:

• The Viking landers conducted experiments on Mars to search for signs of life.
• The Labeled Release (LR) experiment aimed to detect metabolic activity in Martian soil samples.

Purpose of the Study:

• To analyze the thermal sensitivity of the active agent detected in the Viking LR experiment.
• To evaluate whether the LR results are more consistent with biological or chemical processes on Mars.

Main Methods:

• Testing stored surface samples at reduced temperatures before initiating the LR active sequence.
• Heating incubation mixtures to 50 degrees C to release trapped radioactive gas.
• Analyzing thermal decomposition data using Arrhenius plots to calculate activation energy.

Main Results:

• Activity in the LR experiment was significantly diminished in samples stored at approximately 10 degrees C.
• The thermal sensitivity observed is consistent with a biological agent.
• Analysis of thermal decomposition data provided activation energy for the Mars agent.
• Evidence suggests involvement of more than one carbon substrate in the LR reaction.

Conclusions:

• The thermal sensitivity of the Mars active agent supports a biological explanation for the LR experiment.
• However, the data do not definitively rule out a chemical origin for the observed activity.
• Further investigation is needed to resolve the ambiguity between biological and chemical interpretations.