Planetary protection is a discipline that is focused on avoiding harmful contamination by ensuring that spacecraft destined for sensitive biological targets avoid harmful contamination of the target body from terrestrial contamination. The Outer Space Treaty of 1967 Article IX states that “studies of outer space, including the Moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination” which is referred to forward planetary protection. Notably, backward planetary protection is also traced to Article IX which states “also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter” focusing on ensuring that no negative impacts of the Earth’s biosphere result from sample return missions from biological targets of interest.1 The Committee of Space Research (COSPAR) has assembled a Panel on Planetary Protection (PPP) together to develop and curate an international scientific guideline for missions implementing planetary protection. This released guidance represents the international scientific consensus as an accepted path for compliance with the Outer Space Treaty.2 The COSPAR PPP is a means in which each space Agency is represented and meets multiple times per year to discuss pertinent issues to ongoing and upcoming missions as well as research and technology planning as it pertains to policy updates. Proposals for updated science reviews and policy suggestions can be put forth by any member of the public and presented to the panel. These proposals are then discussed and voting members from each country vote to accept, reject, or request additional studies and information. If a policy update is approved the policy is then updated, voted on by the COSPAR PPP members, then formally approved by the COSPAR Bureau. Agency policies are then informed by the updated COSPAR policy.3, 4

NASA has recently updated its planetary protection policy over the course of the past three years. NASA Policy Directive 8700.1F, NASA Policy for Safety and Mission Success details NASA’s responsibilities for ensuring the safety of planetary environments as a top-level safety objective.5 NASA Procedural Requirement 8715.24, Planetary Protection Provisions for Robotic Extraterrestrial Missions establishes the roles and responsibilities required to implement NASA missions as well as defines mission risk categories and PP requirements for key phases of the mission life cycle including sample return.3 The NASA Technical Standard 8719.27, Implementing Planetary Protection Requirements for Space Flight provides the detailed technical requirements throughout the mission life cycle to include mission categorization, biological and organic archiving, assembly and testing, avoiding contamination through inadvertent impact, management of robotic mission biological contamination, end of mission disposition, and details the standard spore assay.6 Additionally, the NASA Handbook for planetary protection currently is being updated to address current methods and good manufacturing practices for meeting the NASA technical standard 8719.27.7

Along with the released policy to conduct missions three enabling objectives are leveraged within NASA’s Office of Planetary Protection. These enabling objectives include transparency of policy and mission operations through open communications, leveraging international scientific norms and standards, and enabling the process to incorporate new scientific findings through a scientific consensus process. NASA’s planetary protection policy is shifting from a prescriptive-based approach to a performance-based approach. The prescriptive-based approach defines both the detailed requirement (the what) along with the implementation approach to meet the requirement (the how) whereas the performance-based requirements approach defines the high-level requirement objective allowing maximum flexibility of the end user to establish the implementation approach. This approach also encourages new methods and procedures to be discussed and presented to meet planetary protection objectives. Ability to realize and implement technical and process innovation for resources, time and cost saving with the flexibility to balance trades. The performance-based approach also covers the use of an assurance case. The assurance case is a well-constructed set of claims and sub-claims that are substantiated through a series of robust scientific and engineering evidence. The assurance case allows for complex systems and planetary protection issues to be addressed such as what would be required for sample return, managing crewed missions to Mars, and assessing harmful contamination probabilities for inoculation of the icy world.

Mars-bound landers and rovers that are not life detection missions and not designated to a special region should adhere to typical biological constraints of 5.0 × 105 total spores per spacecraft, 3.0 × 105 total spores per landed elements, and 300 spores/m2. In controlling the robotic biological contamination, implementers typically develop a bioburden accounting system to plan and track the spore allocations across the spacecraft system. The implementation approach for each hardware component is then planned with a series of biological cleaning and microbial reduction steps that include alcohol solvent wiping to heat microbial reduction. Hardware recontamination is then managed by assembling and testing them in cleanrooms (ISO 8 or better) with stringent personnel and facility controls. To verify the cleanliness of the hardware throughout the hardware assembly and testing, a sampling plan is devised to test the hardware surface with a damp water swab or wipe. This is conducted throughout the hardware assembly to capture the multiple surfaces and layers of the spacecraft. Currently, the only internationally approved method for spacecraft verification is the standard spore assay.6 Briefly, this entails extraction of potential biological material from the sampling device via sonication and vortexing, selection of spores through a heat shock treatment of 80 °C for 15 min, cooling the solution down to room temperature, aliquoting the extract into Petri dishes where tryptic soy agar is added, incubated at 32 °C and microbial colony forming units enumerated at 24, 48, and 72 h. This gold standard is traced back to the Viking era in the 1960s where it was determined that the spore was the most likely microorganism to survive on the surface of Mars as well as survive the heat microbial reduction conducted on the Viking spacecraft. While a tried-and-true biological indicator for decades, modern molecular biology approaches might be a viable solution to understand a wider range of biological contamination on the spacecraft surfaces. Molecular biological approaches such as digital PCR (dPCR) can help to quantify the organisms on the surface while metagenomic approaches can help to provide context on the types and functional analysis of the organisms present.

As mission cadence is increasing from member States to commercial space, more spacecraft are being proposed to biological targets of interest (Mars, Europa and Enceladus) and an increase in mission desiring to conduct sample return or life detection, understanding biological contamination on spacecraft surfaces becomes even more important. While the current planetary protection risk posture for robotic missions is to proceed forward with a conservative approach to address harmful contamination and biological safety risks, it is recognized that we cannot leverage this same risk posture for crewed missions. Crewed missions are proceeding forward with a risk posture that we must control microbial contamination whilst preventing harmful contamination. Within NASA one of the key drivers for planetary protection policy technology and research is in support of crewed missions to Mars. As such, planetary protection has developed its technology roadmap to close knowledge gaps and integrated this roadmap into the crewed mission roadmaps (Siegel et. al 2023). This roadmap serves to help understand the interfaces between key engineering and science disciplines such as environmental life support systems as well as crew health and microbiology. To establish new standards, policy topics in the roadmap are addressed then presented within NASA then international scientific consensus is obtained prior to implementation. An example of this is the identification and understanding of knowledge gaps through six COSPAR, NASA and European Space Agency-sponsored workshops.8–12 As planetary protection increases scope from robotic Mars missions to crewed Mars, policy implementation will increase scope from low biomass environments to on-orbit built environments, Mars-built environments, assessment of Mars samples, and ability to discern adverse changes from crew health in the context of planetary environment exposures.

So, with all the changes in policy, implementation and identified knowledge it begs the question what can one do to help advance the discipline? For member States who are planning missions to Mars, it is recommended to design and plan for planetary protection measures in the early hardware design and testing phases. To ensure planetary protection success, the coordination across multiple disciplines such as contamination control, space biology, crew health and materials and process engineering benefits from early discussions in mission design and planning. Through this coordination synergies, can begin to be identified and interface discrepancies can be worked. As an example, in NASA planning for Artemis the early missions are planning for lunar orbit, crew lunar habitat and extraterrestrial activity vehicles which will leverage PP principles as much as feasible for proof of concept in advancing technology readiness levels to close critical knowledge gaps. These knowledge gaps include the development of an appropriate Mars atmospheric models to understand crew habitats and global contamination impacts, microbial monitoring to understand abnormalities in the built environment from Mars environment coming in during extravehicular activities and assessments and modeling of the impact of human contamination and prediction of the “sphere of influence”. In addition to hardware design, research and technology initiated by the research programs in areas such as planetary science, atmospheric modeling, microbiology, molecular biology, bioinformatics are needed now to close knowledge gaps based on COSPAR workshops recommendations. This work can be directly coordinated with the member States COSPAR PPP representative or through the COSPAR PPP directly.