Toward "Safe" Chemicals and Materials on Mars: Knowledge Gaps for Expanding Planetary Protection Requirements.

The United Nations Outer Space Treaty states that the exploration of celestial bodies must avoid "harmful contamination" which may impede scientific exploration by other parties to the treaty. To guide treaty compliance, Planetary Protection regulations promulgated by the Committee on Space Research set limits for microbial contamination of celestial bodies, particularly those that may harbor extant life (e.g., Mars). However, anthropogenically introduced chemicals and materials are not regulated but may cause "harmful contamination" and thus pose a potential threat to scientific exploration. On Earth, threats from anthropogenic chemicals and materials are often managed by considering both potential exposure to the substances and their hazardous properties. The lack of knowledge around hazards to possible extant life on Mars means that chemicals and materials should be designed and used so that their exposure concentrations are minimized. Here, we review possible emission, partitioning, persistence, and transport processes on Mars for anthropogenically introduced chemicals and materials and identify key knowledge gaps. We highlight difficulties and lessons learned from pollution policy development on Earth that could inform interplanetary chemical and material management. This work aims to support the expansion of the Planetary Protection guidelines to include a "No- or Low-Exposure by Design" approach to chemicals and materials on Mars.