[P-CG17] Future missions and instrumentation for space and planetary science

[PCG17-P04] Development of the bread board model of the Life-signature Detection Microscope (LDM)

*Yoshitaka Yoshimura¹, Akihiko Yamagishi², Atsuo Miyakawa², Eiichi Imai³, Satoshi Sasaki⁴, Mita Hajime⁵, Kensei Kobayashi⁶, Yoko Kebukawa⁶, Naoto Sato⁷, Takehiko Satoh⁸, Keigo Enya⁸, Kazuhisa Fujita⁸, Tomohiro Usui⁸ (1.Tamagawa University, 2.Tokyo University of Pharmacy and Life Science, 3.Nagaoka University of Technology, 4.Tokyo University of Technology, 5.Fukuoka Institute of Technology, 6.Yokohama National University, 7.Meiji University, 8.Japan Aerospace Exploration Agency)

Keywords:Fluorescence microscope, Astrobiology, Life exploration

Present Mars is hostile to life, but recent findings tend to support the possible presence of microbes near the Mars surface. MSL Curiosity has found organic compounds [1], the temporal increase of methane concentration in the Martian atmosphere [2], and reduced sulfur compounds such as pyrite in Martian soil [3]. Methane and reduced sulfur compounds can be energy sources to support the growth of chemoautotrophic microbes [4]. The detection of hydrated salts at Recurring Slope Lineae suggested the possible presence of liquid water [5]. Since UV radiation, which is harmful to life, would be shielded by thin layers (less than a millimeter) of dust or regolith [6], microbes could survive under a depth of several centimeters from the surface. Although the Viking mission in the 1970s did not find evidence for life on the Mars surface [7], the sensitivity of the GC-MS (mass spectrometer) was found not to be very high. It was not able to detect 10⁶ microbial cells in 1 gram soil [8, 9], indicating that another life detection program is necessary.
The Life-signature Detection Microscope (LDM), which we have proposed [10], has the potential sensitivity much higher than the Viking instrument. The LDM is based on fluorescent microscopy and detects organic compounds, membrane structures, and catalytic activities stained by fluorescent pigments. This technique is especially useful for the detection of living microbes. It has the potential to visualize a single cell in micron scale. LDM scans about 1 mm³ and detects less than 10⁴ cells in 1 gram regolith, which is comparable to the least populated area of the terrestrial environment, such as the Atacama desert in Chile. If microbes are not detected, we can determine the upper limit of the microbial density, which is useful information to evaluate the risk of human contact with Martian microbes in future manned explorations.
We have developed the bread board model (BBM) of LDM which is composed of 4 parts: a sample chamber, a light source, a microscope, and a CMOS image sensor. The sample chamber has a sample unit which has a sample holder, 2 pigment solution tanks, a filter unit for concentrating cells. By moving the sample chamber, 1 mm³ of the bottom of the sample holder and a filter unit are photographed by the image sensor through the microscope. The BBM successfully detected and visualized bacteria added in a Mars simulant, MGS-1, at a density of 10⁴ cells g^-1.

References
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[6] Mancinelli, R. L., et al., Planetary and Space Science, 48 (2000) 1093-1097.
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[10] Yamagishi, A., et al., Trans. JSASS, Aerospace Technology Japan, 16 (2018) 299-305.