NRC Recommends New Method of Determining Planetary Protection Threat to Icy Bodies

The National Research Council (NRC) has recommended a new method of calculating the possibility of microorganisms on spacecraft sent to study icy bodies in the solar system contaminating the objects they are sent to examine — called forward contamination.

The report, Assessment of Planetary Protection Requirements for Spacecraft Missions to Icy Solar System Bodies, looks at how to prevent contamination of bodies such as Jupiter’s moon Europa, Saturn’s moon Enceladus or Neptune’s moon Triton.   A 2000 NRC report made recommendations about planetary protection requirements for Europa, but much has been learned since then.   NASA asked the NRC to relook at the requirements.

Planetary protection requirements for the outer planets have been based on the Coleman-Sagan formula that calculates the probability of a spacecraft mission introducing a single microorganism that could grow in the environment of the target body.  According to the new NRC study, the 2000 Europa study recognized the shortcomings of the Coleman-Sagan formula in estimating the risk of forward contamination and this new study recommends a different approach entirely.

Historically, NRC planetary protection recommendations have become international standards through the Committee on Space Research (COSPAR) of the International Council of Science (ICSU).  In 2009, two workshops sponsored by COSPAR led to recommendations for a simplified version of the Coleman-Sagan formula and then to NASA asking the NRC to look at the issue.  This NRC committee found “no scientifically or logically defensible path for improving estimates of factors” for the Coleman-Sagan formula as NASA requested, however.  Instead, it recommends a “binary decision matrix”  — a series of yes/no questions — similar to what the NRC previously recommended (and COSPAR adopted) for samples being returned to Earth. 

The new NRC report argues that its binary decision matrix provides a “more robust basis for determining the appropriate level of planetary protection … because such a procedure would not compound inaccurate and non-independent estimates of probability factors.”

The NASA Advisory Council (NAC) Planetary Science Subcommittee (NAC-PSS) will meet tomorrow and Wednesday.  It is scheduled to be briefed on this new NRC report tomorrow afternoon at 2:45 pm ET according to the current agenda.  The chair of the study was Mitchell Sogin of the Marine Biological Laboratory and the vice-chair was Geoffrey Collins of Wheaton College.   Collins is on the NAC-PSS agenda to discuss the report’s recommendations.