Radiation-driven Prebiotic Chemistry and Biosignatures Detection

Introduction

Earth's prebiotic chemistry is based on water and thermal sources (internal or external to the Earth)^1,2. In contrast, the prebiotic chemistry of extraterrestrial systems (Mars, Europa, Titan, Enceladus, etc.) is primarily driven by radiation sources^3–5. Recent work leveraging Martian and ocean world natural and synthetic analog materials was used to classify biotic and abiotic organics in the context of multiple planetary missions (with Curiosity, Perseverance, Rosalind Franklin, and Dragonfly)^6–9. Our experiments yielded a chemical network that abiotically produced building blocks of life (e.g., amino acids up to small-peptides and thiamine and nucleobases up to nucleotides) when synthetic analogs were hydrolyzed in contact with salts and/or exposed to X-/Ɣ-rays and proton irradiation^7,10. The different irradiation simulations on natural and synthetic analog materials analyzed by spaceflight instruments and/or high-resolution mass spectrometry assessed the question: How fast may the transition from prebiotic abiotic chemistry to biotic chemistry take place? A “primitive biochemistry transition” would occur and contradicts the expectation of a clear biotic-abiotic boundary between the production of polymers abiotically and biologically in a primitive environment. Indeed, our experiments and some meteoritic data revealed the production of small biopolymers abiotically from a few hundred to tens of thousands of years^10–12.

Materials and Methods

To address the influence of different radiation sources on organic matter transformation as a pure standard or in a matrix/medium analog to extraterrestrial surfaces, we got access to multiple radiation facilities (SOLEIL-France and CLS-Canada synchrotron for X-rays, GSFC-NASA-USA for Ɣ-ray and protons radiations) and analyzed with X-ray, infrared spectroscopy and GC-MS/orbitrap.

To simulate Mars near surface environment, we first studied soft/mid X-rays that could be indirectly produced by the main elements in the Martian regolith (secondary X-rays by carbon (0.28 keV), silica (1.74 keV), sulfur (2.31 keV), chlorine (2.62 keV), or iron (6.40 keV)). Those experiments focused on amino acids (L-Ala, L or D/L-Phe), peptides (Ala-Gly), carboxylic acids (trimesic, lignoceric, and benzoic acids), nucleobases (adenine and uracil), and organics detected by the Sample Analysis at Mars (SAM) at Gale crater (chlorobenzene and thiophene).

We then simulated the radiative conditions at higher energies for Mars and ocean worlds (using γ-rays at 1-300 krad equivalent to 6 months-1000 Titan years’ simulation, for instance, and protons at 200 MeV – e.g., a few Titan months) and chemical environment that tropospheric aerosols or surface deposits may undergo on Titan to forecast Dragonfly operations, analysis, and interpretations.

 

Results

Low radiation energies enhance the production of building blocks of life (e.g., nucleobases, amino acids, sugars) (Fig. 1).

Low eradiation energies induce interactions between organic matter and inorganic soluble or solid material (bond and/or form organo-mineral/salt products).

While low energy radiation enhanced the production of building blocks of life (BBLs), high energy radiation degraded faster the prebiotic precursors than  produced the BBLs (Fig. 2). High radiation energies (photons and particles) benefit to the polymerization.

Conclusions

Within protected environments (e.g., Mars subsurface environments – below 10 cm – from SAM-MSL data and investigation for MOMA-ExoMars), biosignatures may be preserved for at least 100 million years thanks to salts.

A “primitive biochemistry transition” may have occurred in crater impacts few billion years ago (e.g., at Gale and Jezero craters) and contradicts the expectation of a clear biotic-abiotic boundary between the production of polymers abiotically and biologically in a primitive environment. Indeed, our experiments and some meteoritic data revealed the abiotic production of small biopolymers from a few hundred to tens of thousands of years driven by radiation and a catalytic substrate.

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