Lindsay A. Rutter†, Abhishek Sharma†, Ian Seet, David Obeh Alobo, An Goto, and Leroy Cronin*
School of Chemistry, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK. *Corresponding author Email: Lee.Cronin@glasgow.ac.uk †Equal contribution
Abstract Detecting life beyond Earth requires biosignatures that do not depend on the chemistry of known organisms. Molecular assembly (MA), derived from Assembly Theory (AT), quantifies how difficult it is to build a molecule from basic building blocks, linking complexity directly to selection and evolution. Here, we show that MA can serve as a universal, experimentally measurable biosignature that is both interpretable and experimentally measurable. Unlike information-theoretic measures, MA can be inferred directly from mass spectrometry data without structural elucidation. We demonstrate this using a machine learning model trained on standardised single-stage (MS¹) spectra, which predicts MA with three-fold lower error than baseline methods. Simulated multi-stage (MSⁿ) data reveal that small instrumental variations can double prediction error, highlighting the importance of calibration. These findings establish molecular assembly as a physically grounded, quantifiable biosignature measurable by mass spectrometry whose interpretation depends on careful control of instrumental effects, offering a scalable route to life detection on future planetary missions.