The Biology of Biosignature Detection: Rationale and Experimental Frameworks for Biological Validation

Abstract

Advances in life detection technologies and lessons from past missions now position us to directly explore microbial life on Mars and address fundamental questions about its habitability. These breakthroughs allow us to investigate microbial processes that can detect both extant and extinct life on Mars. By focusing on microbiology-driven questions and integrating experiments into planetary missions, we aim to uncover the metabolic and biochemical signatures that indicate life, past or present, on the Martian surface. In this report, we propose innovative instruments and instrument payloads designed to detect microbial life on Mars while addressing its unique, challenging conditions.

Over the past fifty years, scientists have advanced our understanding of life's limits on Earth by identifying environments with exceptionally low cellular abundance. Technical breakthroughs in analytical, chemical, and experimental approaches have driven these insights, enabling researchers to study life in an agnostic way and recognize terrestrial biases. In parallel, they have made significant progress in detecting biomarkers associated with ancient life. Biological processes permeate the Earth’s crust, driving interactions between nutrients and habitats that, over geologic time, create the diverse ecologies we consider habitable. However, favorable environmental conditions do not indicate that these environments are inhabited.

In 1975-76, the Viking missions represented humanity's first attempt to determine the potential for life beyond Earth. Although they showed promise, their ambiguous results prompted subsequent planetary missions to focus on geologic conditions for habitability. Over the decades, mission strategies targeted narrow environmental conditions based on the minimum requirements for life by "following the water." As interdisciplinary research in microbiology has grown, we can now propose a new era of planetary missions that directly investigate the presence and activity of microorganisms, focusing on key cellular processes such as metabolism.

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