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3 Responses to the Statement of Task and Recommendations
Pages 35-46

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From page 35...
... This chapter investigates some additional arguments regarding planetary protection requirements for a sample return mission from the martian moons. The organization of this chapter is designed to provide the committee's answers to the questions posed in the statement of task (see the Preface)
From page 36...
... Sterilization During Hypervelocity Impact on Phobos/Deimos Surfaces The SterLim team calculated a microbe survival rate ~ 0.1 for velocity <2 km/s, based on impact experiments. The JAXA team reworked the impact sterilization model using SPH and trajectory analysis, resulting in a survival rate of only 10−4.
From page 37...
... Sterilization by Radiation on Phobos/Deimos Surfaces The SterLim team used a sterilization model based on experimental data. The JAXA team used a similar model but averaged the microbial survival rate for its specific depth by integrating the survival rate in the depth direction and then dividing by the depth.
From page 38...
... Assuming life exists in the surface and near-surface regions of Mars, the flux ratio is a proxy for the relative contribution of spacecraft-transported martian life-forms arriving on Earth compared to those arriving on Earth naturally. The JAXA team calculated that the maximum mixing ratio of martian material to Phobos regolith for the material coming from the Zunil impact was ~100 ppm.3 Therefore, a 100 g sample collected by a nominal Phobos sample return mission will return 10−5 kg of Mars-derived material to Earth.
From page 39...
... Almost all Mars rocks material fall in the oceans or impact rural areas and are never detected. The tiny fraction of Mars rocks that end up in collections comes into researchers' flux calculations only in determining the ratio of Mars rocks in total meteorites.
From page 40...
... For the Phobos sample, 1 in 104 survived impact on Phobos, and of these 1 in 104 survive radiation exposure on Phobos, for a net ratio of 10−8. So, the ratio of surviving microbes in Mars rocks to those in the Phobos sample is the mass ratio 1013 times the relative survival ratio (10−9/10−8)
From page 41...
... Recommendation: After considering the body of work conducted by the SterLim and JAXA teams, the effect of desiccation on the surfaces of the martian moons, and the relative flux of meteorite- to spacecraft-mediated transfer to Earth, the committee recommends that samples returned from the martian moons be designated unrestricted Earth return. TASK 3 -- DIFFERENCES BETWEEN PHOBOS AND DEIMOS IN THE CONTEXT OF PLANETARY PROTECTION The third task of the committee was to elaborate In what specific ways is classification of sample return from Deimos a different case than sample return from Phobos?
From page 42...
... However, as no microbe has been so far reported from a martian meteorite, this sug gests that the martian bioload is small, possibly smaller than the value assumed by the SterLim and JAXA teams. Finding: The committee finds that the study of martian meteorites provides important context for studies of Mars and its moons and limited information (e.g., mass and flux to Earth)
From page 43...
... The committee limits its response to this task to comments on three specific topics, uncertainty quantification, implications for Mars sample return missions, and the publication of the work of the SterLim and JAXA teams. Uncertainty Quantification The work of the SterLim and JAXA teams provides prime examples of attempts to reach a specific conclusion about real-world activities based on combining the results from multiple numerical simulations and laboratory experiments.
From page 44...
... Therefore, the starting point of the quantitative evaluations undertaken by the SterLim and JAXA teams in terms of the number of colony-forming units in the martian regolith (see "Potential Microbial Density on the Martian Surface," in Chapter 2) will very likely be invalid when considering MSR.
From page 45...
... Publication of the Work of the SterLim and JAXA Teams Planetary protection policies and the studies underlying them have a reputation in some circles as being based on faulty or outmoded ideas and approaches. The immense amount of work undertaken by the SterLim and JAXA teams makes it clear that these criticisms are, at least in this case, unfounded.


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