Investigating Microbial Biosignatures in Aeolian Environments Using Micro-X-Ray: Simulation of PIXL Instrument...

Area of Science:

• Astrobiology and Planetary Science
• Geochemistry and Mineralogy
• Microbiology and Biosignature Detection

Background:

• NASA's Mars 2020 mission, utilizing the Perseverance rover, aims to assess Mars' past habitability and search for ancient life, particularly in Jezero crater.
• The Planetary Instrument for X-ray Lithochemistry (PIXL) is crucial for detecting microbial biosignatures by analyzing fine-scale geological textures and chemical compositions non-destructively.
• PIXL is the first micro-X-ray fluorescence (μXRF) spectrometer deployed on a Mars rover, necessitating the development of effective analytical strategies.

Purpose of the Study:

• To establish guidelines for identifying and investigating microbial biosignatures in aeolian environments using PIXL-analogous μXRF techniques.
• To analyze geochemical and textural variations in buried microbial mats within a modern wet aeolian setting.
• To assess how technical constraints and user approaches influence biosignature investigation using PIXL-like sampling strategies.

Main Methods:

• Collected and analyzed samples from a modern wet aeolian environment at Padre Island, Texas, containing buried microbial mats.
• Employed μXRF techniques analogous to PIXL's operational methods to analyze samples from the surface down to approximately 40 cm depth.
• Conducted an interactive survey using μXRF data to evaluate different user strategies for investigating biosignature-bearing datasets with PIXL-like sampling.

Main Results:

• Microbial mats were identified, associated with heavy-mineral lags, exhibiting distinct textural and geochemical characteristics (rich in iron and titanium) due to trapped minerals.
• Buried microbial mats showed diffuse textures resulting from gas-filled void expansion/contraction, differentiating them from abiotic facies like cross-stratification and adhesion ripple laminations.
• μXRF analysis successfully detected these intrinsic characteristics, confirming their potential as detectable biosignatures. User surveys revealed that technical constraints and diverse scientific approaches significantly impact biosignature investigation.

Conclusions:

• Microbial biosignatures in aeolian environments possess detectable geochemical and textural signatures that can be identified using μXRF analysis, analogous to PIXL's capabilities.
• Effective biosignature detection on Mars requires careful consideration of PIXL's technical constraints, prioritizing measurements, and adopting a multidisciplinary approach.
• Understanding abiotic facies and their signatures is crucial for accurately interpreting potential biosignatures and supporting or refuting their existence in the Martian context.