Planetary protection

Planetary protection is the term used to describe a guiding principle in design of an interplanetary mission that aims to prevent biological contamination of both the target celestial body and the Earth. This principle arises from the scientific need to preserve planetary conditions for future biological and organic constituent exploration – especially exobiology/astrobiology. The incorporation of geoethical issues in planetary and space research and astrobiology widens the classical concept of Planetary protection, considering, besides the organics-bearing perspective, the abiotic nature and all features of the planetary bodies and their planetary geodiversity. It also aims to protect the Earth and its biosphere from potential extraterrestrial sources of contamination in the event of a sample return mission. The need for planetary protection measures is strongest for missions designed to return a sample of another planet or celestial body to the earth.

Process

The spacecraft must be sterilized before leaving Earth in order to minimize the risk of depositing Earth-originating biological material at the destination. The return vehicle must then be designed such that the sample is returned in highly reliable "bio-container" with measures in place to dispose of any parts of the vehicle which could have been contaminated before re-entry into the Earth's biosphere.

The Committee on Space Research categorizes the missions into 5 groups:

• Category I: Any mission to the Sun, Mercury, other locations not of interest for studying prebiotic chemistry or the origin and evolution of life.
• Category II: Any mission to the Earth's Moon, Venus, comets, Jupiter, Pluto/Charon, Kuiper Belt Objects, other locations of interest for studying prebiotic chemistry and the origin of life but for which there is an insignificant probability of contamination with Earth life.
• Category III: Flyby and orbiter missions to locations with the potential to host life and for which there is a possibility of contamination by Earth life; e.g., Mars, Europa, Titan or Enceladus.
• Category IV: Lander or probe missions to locations with the potential to host life and for which there is a possibility of contamination by Earth life; e.g., Mars, Europa, Titan or Enceladus.
• Category V: Any earth return mission. Missions returning samples from locations with the potential to support life are considered 'Restricted Earth Return' and returned samples must be contained at levels more stringent than Biosafety level 4. Samples from locations judged unlikely to support life are considered 'Unrestricted Earth Return' and merit no constraints for planetary protection purposes.

This classification can change due to new scientific knowledge.

After receiving the mission category a certain level of biological burden is allowed for the mission. In general this is expressed as a 'probability of contamination', but in the case of Mars this has been translated into a metric for the number of Bacillus spores per surface area and present in total on or within the spacecraft: 300 spores per m² free surface, but not more than 3E5 spores in total (category IVa). The amount should be ten thousand times less if area of special protection should be visited.

Clean room assembly and microbial reduction through heat, chemicals or radiation are the basic techniques used to accomplish microbial control when this is necessary for a mission.

The discovery of extremophiles on Earth surviving temperatures that we previously thought to be lethal to all life demonstrate how difficult it can be to prevent biological contamination. It is widely claimed that a common bacterium, Streptococcus mitis, was found to have accidentally contaminated the Surveyor 3 camera prior to launch and survived dormant in this harsh environment for two and a half years. However, this claim is no longer taken seriously by NASA (see Myth of Streptococcus mitis on the moon).

Measures currently in use for scientific exploration include dry-heating of satellites, sterilizing wipes and aseptic integration of components. These add a significant burden to mission designers and integration teams. However, there is consensus that this is required to prohibit the possible microbial contamination of other planets.

See also

• Forward-contamination
• Back-contamination
• Cassie Conley, current NASA Planetary Protection Officer

General references

• Sagan, C., and S. Coleman (1965). "Spacecraft sterilization standards and contamination of Mars". Journal of Astronautics and Aeronautics 3 (5): 22–27. 
• C. Mileikowsky, F. A. Cucinotta, J. W. Wilson, B. Gladman, G. Horneck, L. Lindegren, J. Melosh, Hans Rickman, M. Valtonen, J. Q. Zheng (2000). "Risks threatening viable transfer of microbes between bodies in our solar system". Planetary and Space Science 48 (11): 1107–1115. Bibcode 2000P&SS...48.1107M. doi:10.1016/S0032-0633(00)00085-4. 
• Rummel J. D., Billings L. (2004). "Issues in planetary protection: policy, protocol and implementation". Space Policy 20 (1): 49–54. doi:10.1016/j.spacepol.2003.11.005. 

• Benton C. Clark (2004). "Temperature–time issues in bioburden control for planetary protection". Advances in Space Research 34 (11): 2314–2319. Bibcode 2004AdSpR..34.2314C. doi:10.1016/j.asr.2003.06.037. 
• A. Debus (2004). "Estimation and assessment of Mars contamination". Advances in Space Research 35 (9): 1648–1653. Bibcode 2005AdSpR..35.1648D. doi:10.1016/j.asr.2005.04.084. PMID 16175730. 
• J. Nellen, P. Rettberg, G. Horneck and W.R. Streit (2006). "Planetary protection – Approaching uncultivable microorganisms". Advances in Space Research 38 (6): 1266–1270. Bibcode 2006AdSpR..38.1266N. doi:10.1016/j.asr.2005.10.026. 
• L. I. Tennen (2006). "Evolution of the planetary protection policy: conflict of science and jurisprudence". Advances in Space Research 34 (11): 2354–2362. Bibcode 2004AdSpR..34.2354T. doi:10.1016/j.asr.2004.01.018. 
• L. Perek (2006). "Planetary protection: lessons learned". Advances in Space Research 34 (11): 2354–2362. Bibcode 2004AdSpR..34.2368P. doi:10.1016/j.asr.2003.02.066. 
• J. D. Rummel, P. D. Stabekis, D. L. Devincenzi, J. B. Barengoltz (2002). "COSPAR's planetary protection policy: A consolidated draft". Advances in Space Research 30 (6): 1567–1571. Bibcode 2002AdSpR..30.1567R. doi:10.1016/S0273-1177(02)00479-9. 
• D. L. DeVincenzi, P. Stabekis and J. Barengoltz (1996). "Refinement of planetary protection policy for Mars missions". Advances in Space Research 18 (1–2): 311–316. Bibcode 1996AdSpR..18..311D. doi:10.1016/0273-1177(95)00821-U. PMID 11538978. 
• J. Barengoltz and P. D. Stabekis (1983). "U.S. planetary protection program: Implementation highlights". Advances in Space Research 3 (8): 5–12. Bibcode 1983AdSpR...3....5B. doi:10.1016/0273-1177(83)90166-7. 
• L. P. Daspit, J. A. Stern, E. M. Cortright (1975). "Viking heat sterilization—Progress and problems". Acta Astronautica 2 (7–8): 649–666. doi:10.1016/0094-5765(75)90007-7. 
• [1]

External links

• No bugs please, this is a clean planet! (ESA article)
• COSPAR planetary protection policy, July 2008 (COSPAR article)
• International Committee Against Mars Sample Return (ICAMSR website)
• NASA Planetary Protection Website
• JPL Develops High-Speed Test to Improve Pathogen Decontamination at JPL.
• Geoethics in Planetary and Space Exploration