Raman Spectroscopic Techniques for Planetary Exploration: Detecting Microorganisms through Minerals.

Area of Science:

• Astrobiology
• Planetary Science
• Spectroscopy

Background:

• Raman spectroscopy offers chemical fingerprints for materials, crucial for extraterrestrial life detection.
• Detecting low-level biomarkers within or beneath minerals on planetary surfaces presents a significant challenge.
• Light scattering by minerals can impede deep sample analysis.

Purpose of the Study:

• To demonstrate the detection of microorganisms behind mineral layers using time-resolved Raman spectroscopy (TRRS).
• To assess the capability of TRRS for depth-selective analysis of subsurface biomarkers in planetary exploration.

Main Methods:

• Utilized time-resolved Raman spectroscopy (TRRS) with 3 ps laser pulses and a 250 ps gated intensified CCD camera.
• Employed 440 nm excitation under resonance conditions to enhance carotenoid detection in extremophiles.
• Tested detection through translucent calcite (5 mm) and transparent halite (20 mm) mineral layers.

Main Results:

• Successfully detected carotenoid-containing microorganisms (Deinococcus radiodurans and Chroococcidiopsis) through mineral layers.
• Achieved depth selectivity, reducing interference from mineral surfaces and fluorescent backgrounds.
• Demonstrated detection through significant thicknesses of both translucent and transparent minerals.

Conclusions:

• TRRS provides depth-selective analysis capabilities for scattering samples, overcoming limitations of conventional Raman spectroscopy.
• This method holds significant potential for in-situ detection of subsurface microorganisms and biomarkers in future planetary exploration missions.