日本地球惑星科学連合2018年大会

講演情報

[EJ] 口頭発表

セッション記号 P (宇宙惑星科学) » P-PS 惑星科学

[P-PS07] 火星と火星圏の科学

2018年5月20日(日) 10:45 〜 12:15 201A (幕張メッセ国際会議場 2F)

コンビーナ:宮本 英昭(東京大学)、臼井 寛裕(東京工業大学地球生命研究所)、松岡 彩子(宇宙航空研究開発機構 宇宙科学研究所 太陽系科学研究系、共同)、Sushil K Atreya (University of Michigan Ann Arbor)、座長:宮本 英昭臼井 寛裕

12:00 〜 12:15

[PPS07-12] Scientific significance of searching living cells on Mars surface by Life Detection Microscope (LDM )

*吉村 義隆1山岸 明彦2佐藤 毅彦3宮川 厚夫2今井 栄一4佐々木 聰5小林 憲正6癸生川 陽子6薮田 ひかる7長沼 毅8三田 肇9藤田 和央3臼井 寛裕10 (1.玉川大学農学部、2.東京薬科大学生命科学部、3.宇宙航空研究開発機構宇宙科学研究所、4.長岡技術科学大学生物機能工学専攻、5.東京工科大学医療保健学部、6.横浜国立大学大学院工学研究院、7.広島大学大学院理学研究科地球惑星システム学専攻、8.広島大学大学院生物圏科学研究科、9.福岡工業大学工学部、10.東京工業大学地球生命研究所)

Past trial of direct detection of life on Mars by 1970's Viking mission ended up with a negative conclusion [1]. Whereas, numbers of new finding provided by Mars exploration missions in the last decade indicate that there are good reasons to perform another life detection program. The sensitivity of the gas chromatograph mass spectrometer onboard the Viking mission was not very high, and was not able to detect the microbes 106 cells in 1 gram clay [2,3]. Here we propose Life Detection Microscope (LDM) that has much higher sensitivity than the instrument onboard Viking. LDM will achieve high sensitivity of microbial cells by observing sufficient volume of soil sample on Mars. It is also important to have the resolution 1 micrometer to detect microbial cells.
Resent observations on Mars have found the evidences of past water activities. MSL Curiosity has found the temporal increase of methane concentration in Martian atmosphere [4]. The presence of reduced sulfur compound such as pyrite in Martian soil was also detected by MSL [5]. Methane and reduced sulfur compound can be the energy source to support the growth of chemoautotrophic microbes [6]. Possible presence of liquid water at Recurring Slope Lineae has been supported by the detection of hydrated salts [7]. The presence of organic compounds of Martian origin has been reported [8]. These evidences tend to support the possible presence of living microbes near the surface of Mars.
Physical and chemical limits for terrestrial life have been major foci in astrobiology [9], and are summarized in ref. [6]. Combining the environmental factors, anywhere in the Martian environment where we can find the three components, water molecules, reducing compounds and oxidative compounds could be an environment where life can be sustained for long periods of time, if other factors such as temperature, pressure, UV and other radiations permit [6]. Among these factors, most of the factors including ionic radiation, can be endured by terrestrial extremophiles. Only UV can kill the most UV-resistant microbes within minutes. However, UV can be shielded by a-few-centimeter sail layer. These evaluation lead to the conclusion that the Martian soil under a few cm can be the place to support the growth of microbes, if the water activity is higher than 0.6.
We will report the current status of the development of the LDM. We propose to search for cells from a depth of about 5 - 10 cm below the surface, which is feasible with current technology. Microscopic observation has the potential to detect single cells. We have developed the solution and combination of fluorescence pigments to detect organic compounds, and to differentiate organic compounds surrounded by membrane. The subsequent analysis of amino acids, in the following mission, will provide the information needed to elucidate the origin of the cell.
LDM that we propose here could detect less than 104 cells in 1 gram clay [6]. Our life-detecting instrument has the sensitivity that is two orders of magnitude higher than the one onboard Viking. LDM is capable of identifying what we think to be the most fundamental features that a cell should possess to constitute life. Our investigation Goals are the followings. 1) Identify cell-like structure in which organic compounds are enveloped by membrane, which may represent Martian life. 2) Search for any type of organic compounds in Mars surface samples. The compounds include cells, other biological materials, and abiotic polycyclic aromatic hydrocarbon (PAH). 3) High-resolution characterization of regolith and dust particles. Scientific significance will be addressed in this report.

References
[1] Margulis, L. et al. J. Mol. Evol. 14, 223-232 (1979)
[2] Glavin, et al, Earth Planet. Scie. Lett., 185, 1-5 (2001)
[3] Navarro-González, et al., Proc. Natl. Acad. Sci. USA. 103, 16089-16094 (2006)
[4] Webster, C.R. et al. Science Express Dec. 16 (2014)
[5] Ming, D.W. et al. Science Express Dec.19 (2013)
[6] Yamagishi, A. et al. Biol. Scie. Space, 24, 67-82 (2010)
[7] Ojha, L. et al. Nature Geoscie. 8, 829-832 (2015)
[8] Freissient, C. et al. J. Geophys. Res. Planets (2015)
[9] Marion, G.M. et al. Astrobiol. 3, 785-811 (2003)