Abstract EANA2026-33

Astrobiology is still constrained by a carbon-water reference model, although cryogenic planetary and exoplanetary environments may require broader but physically testable biochemical hypotheses. This study develops a multi-scale in silico framework for evaluating boron-nitrogen alternative biochemistry in liquid-ammonia environments. The work does not claim the existence or detection of non-terrestrial life; instead, it defines a falsifiable parameter space in which a hypothetical B-N biochemical architecture can be constrained by chemistry, thermodynamics, target selection, and observability.

The framework combines four levels of analysis. First, exoplanet candidates are filtered using a cold ammonia belt temperature window of approximately 195-240 K, together with atmospheric retention constraints based on Jeans escape. Second, a thermal feasibility model estimates whether internal chemical energy could maintain a functional temperature offset in an ammonia-rich environment. Third, molecular-level plausibility is assessed through B-N structural motifs, including boron-nitrogen information-bearing analogues and boron nitride nanotube-like transport structures, under the low dielectric conditions of liquid ammonia. Fourth, possible observational consequences are evaluated as non-diagnostic biosignature hypotheses, with explicit attention to false positives.

Preliminary calculations identify a small subset of priority exoplanetary targets from a larger archive-scale candidate pool, while thermodynamic and membrane-transport constraints suggest that selected B-N motifs may be treated as testable chemical architectures rather than unsupported biological claims. A representative thermal scenario considers an external environment near 213 K and an internal target temperature near 233 K, requiring an estimated NH3BH3-based chemical fuel flux on the order of 10^-8 mol s^-1. In the observational layer, NH3 depletion near the infrared spectral region is treated only as a candidate environmental signature, not as evidence for life, because photochemistry, atmospheric mixing, haze, and retrieval degeneracies could produce similar patterns.

By separating chemically plausible components from speculative biological interpretation, this framework turns boron-nitrogen alternative biochemistry into a conservative astrobiological screening problem. It may support future work on exoplanet habitability, alternative biosignatures, and mission-oriented strategies for avoiding false-positive life detection in non-water solvent environments.