从火星卫星返回样品的微生物污染概率的评估II：火星卫星上微生物的命运
Assessment of the probability of microbial contamination for sample return from Martian moons II: The fate of microbes on Martian moons
摘要：
本文介绍了一个火星-卫星系统中微生物运输的案例研究。我们通过一项同伴研究（Fujita等人），使用撞击物理学研究了火星卫星上潜在撞击运输微生物的空间分布。我们使用了之前研究的灭菌数据。我们认为微生物主要来自火星上的祖尼尔陨石坑。我们发现，70-80%的微生物很可能分散在月球表面，除了流星体产生的厚厚的喷出物沉积物中的微生物外，由于辐射而迅速灭菌。另外20-30%可能被火星岩石撞击产生的陨石坑中坍塌层形成的厚风化层屏蔽了辐射。在厚厚的喷出物沉积物中可能存活的微生物总数估计比火星陨石坑低3-4个数量级。由于辐射灭菌，微生物浓度在水平方向上是不规则的，并且在很大程度上依赖于深度。在火卫一和火卫二上，被运输的微生物的存活率分别只有1 ppm和100 ppm，这表明运输过程和辐射严重影响了微生物的存活。对火星卫星微生物采样概率进行了研究。我们建议，从火星卫星的样品返回任务被归类为30 g样品和10 cm深度采样的无限制地球返回任务，即使在我们保守的情况下。我们还进行了全面的统计分析，包括采样概率的输入参数的不确定性的影响，采样的火卫一的风化层。返回样品最有可能受到微生物污染的概率估计比空间研究委员会（空间研委会）行星保护政策所确定的标准低两个数量级。
英文摘要：
This paper presents a case study of microbe transportation in the Mars-satellites system. We examined the spatial distribution of potential impact-transported microbes on the Martian moons using impact physics by following a companion study (Fujita et al.). We used sterilization data from the precede studies. We considered that the microbes came mainly from the Zunil crater on Mars. We found that 70-80% of the microbes are likely to be dispersed all over the moon surface and are rapidly sterilized due to radiation except for those microbes within a thick ejecta deposit produced by meteoroids. The other 20-30% might be shielded from radiation by thick regolith layers that formed at collapsed layers in craters produced by Mars rock impacts. The total number of potentially surviving microbes at the thick ejecta deposits is estimated to be 3-4 orders of magnitude lower than at the Mars rock craters. The microbe concentration is irregular in the horizontal direction and is largely depth-dependent due to the radiation sterilization. The surviving fraction of transported microbes would be only 1 ppm on Phobos and 100 ppm on Deimos, suggesting that the transport processes and radiation severely affect microbe survival. The microbe sampling probability from the Martian moons was also investigated. We suggest that sample return missions from the Martian moons are classified into Unrestricted Earth-Return missions for 30 g samples and 10 cm depth sampling, even in our conservative scenario. We also conducted a full statistical analysis for sampling the regolith of Phobos to include the effects of uncertainties in input parameters on the sampling probability. The most likely probability of microbial contamination for return samples is estimated to be two orders of magnitude lower than the criterion defined by the planetary protection policy of the Committee on Space Research (COSPAR).
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