Prebiotic Chemistry Insights for Dragonfly II: Thermodynamic Favorability of Nucleobases, Ribose, and Fatty Acids in Selk Crater on Titan

Saturn’s moon Titan is a prime destination for investigating prebiotic chemistry beyond Earth, particularly at impact crater sites where transient liquid water may have enabled aqueous reactions between organic molecules.

Selk crater represents one such environment and is a primary target of NASA’s Dragonfly mission. Here, we present a thermodynamic assessment of nucleobases, ribose, and fatty acids formed from simple atmospheric precursors (HCN and C₂H₂) within a Selk-sized aqueous melt pool across varying ammonia (NH₃) abundances. We find that ammonia acts as a chemical gatekeeper for molecular accessibility.

Left: mosaic of the incidence-angle-corrected SAR swaths within the ROI. Right: geomorphological map of the ROI. Source: Composition, Roughness, and Topography from Radar Backscatter at Selk Crater, the Dragonfly Landing Site, The Planetary Science Journal

In NH₃-free systems, accessibility is restricted to adenine and butanoic acid. Once >=1% NH₃ is introduced, all investigated molecular classes become thermodynamically accessible. Distinct molecular classes have different NH3 sensitivities: nucleobases, ribose, and C2-C6 fatty acids yield peaks at 1% NH₃, and C7-C12 fatty acids yield peaks at 2% NH₃.

The modeled preference for pyrimidines vs. purines and monotonic decline of fatty acid abundance with chain length qualitatively mirror patterns observed in carbonaceous meteorites and returned asteroid samples. We show how molecular distributions and cross-class correlations may provide indirect constraints on Selk’s past aqueous environment, help constrain past ammonia availability, and distinguish abiotic production from potential anomalies.

By coupling thermodynamic predictions with an assessment of Dragonfly’s mass spectrometer (DraMS) capabilities, we posit concrete, testable predictions for evaluating Selk’s prebiotic potential in situ.

Ishaan Madan, Ben K.D. Pearce

Comments: Accepted in Planetary Science Journal, April 2026
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Chemical Physics (physics.chem-ph); Biomolecules (q-bio.BM)
Cite as: arXiv:2604.16249 [astro-ph.EP] (or arXiv:2604.16249v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2604.16249
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Related DOI:
https://doi.org/10.3847/PSJ/ae5f91
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Submission history
From: Ishaan Madan
[v1] Fri, 17 Apr 2026 17:11:17 UTC (795 KB)
https://arxiv.org/abs/2604.16249

Astrobiology, Astrogeology, Astrochemistry,