Exploring molecular assembly as a biosignature using mass spectrometry and machine learning

TL;DR

This paper demonstrates that molecular assembly, measurable via mass spectrometry and predicted by machine learning, can serve as an interpretable and unbiased biosignature for detecting extraterrestrial life.

Contribution

It introduces a machine learning approach to predict molecular assembly from mass spectrometry data, enabling life detection without structural elucidation.

Findings

Machine learning predicts molecular assembly with high accuracy.

Standardization of mass spectrometry data reduces prediction errors.

Molecular assembly serves as an interpretable biosignature for astrobiology.

Abstract

Molecular assembly offers a promising path to detect life beyond Earth, while minimizing assumptions based on terrestrial life. As mass spectrometers will be central to upcoming Solar System missions, predicting molecular assembly from their data without needing to elucidate unknown structures will be essential for unbiased life detection. An ideal agnostic biosignature must be interpretable and experimentally measurable. Here, we show that molecular assembly, a recently developed approach to measure objects that have been produced by evolution, satisfies both criteria. First, it is interpretable for life detection, as it reflects the assembly of molecules with their bonds as building blocks, in contrast to approaches that discount construction history. Second, it can be determined without structural elucidation, as it can be physically measured by mass spectrometry, a property that distinguishes it from other approaches that use structure-based information measures for molecular complexity. Whilst molecular assembly is directly measurable using mass spectrometry data, there are limits imposed by mission constraints. To address this, we developed a machine learning model that predicts molecular assembly with high accuracy, reducing error by three-fold compared to baseline models. Simulated data shows that even small instrumental inconsistencies can double model error, emphasizing the need for standardization. These results suggest that standardized mass spectrometry databases could enable accurate molecular assembly prediction, without structural elucidation, providing a proof-of-concept for future astrobiology missions.