Assessment of the probability of microbial contamination for sample return from Martian moons II: The fate of microbes on Martian moons. (arXiv:1907.07576v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kurosawa_K/0/1/0/all/0/1">Kosuke Kurosawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Genda_H/0/1/0/all/0/1">Hidenori Genda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hyodo_R/0/1/0/all/0/1">Ryuki Hyodo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yamagishi_A/0/1/0/all/0/1">Akihiko Yamagishi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mikouchi_T/0/1/0/all/0/1">Takashi Mikouchi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Niihara_T/0/1/0/all/0/1">Takafumi Niihara</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matsuyama_S/0/1/0/all/0/1">Shingo Matsuyama</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fujita_K/0/1/0/all/0/1">Kazuhisa Fujita</a>
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).
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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