[B-BG02] Interaction between Life, Water, Mineral, and Atmosphere

[BBG02-01] Search for biosignatures on Mars by the Life-signature Detection Microscope (LDM)

*Yoshitaka Yoshimura¹, Akihiko Yamagishi², Atsuo Miyakawa², Satoshi Sasaki³, Eiichi Imai⁴, Keigo Enya⁵, Kensei Kobayashi⁶, Yoko Kebukawa⁶, Tomoka Okada⁶, MITA Hajime⁷, Takeshi Naganuma⁸, Takehiko Satoh⁵, Kazuhisa Fujita⁵, Tomohiro Usui⁵ (1.Tamagawa University, 2.Tokyo University of Pharmacy and Life Science, 3.Tokyo University of Technology, 4.Nagaoka University of Technology, 5.Japan Aerospace Exploration Agency, 6.Yokohama National University, 7.Fukuoka Institute of Technology, 8.Hiroshima University)

Keywords:Fluorescent microscope, Astrobiology

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 detect a single cell and visualizes their shapes, sizes, and other morphological structures at a spatial resolution of 1 µm. The sensitivity can also be as high as desired just by increasing the volume of the sample to be scanned in a reasonable duration of experiments. LDM scans about 1 mm³ and detects less than 10⁴ cells in 1 gram soil, which is comparable to the least populated area of the terrestrial environment on Earth, 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.

Currently, we have been developing the breadboard model (BBM) of LDM. We will report the current status of the BBM and discuss how and where to find biosignatures on Mars.



References

[1] Eigenbrode, J. L., et al., Science, 360 (2018) 1096-1101.

[2] Webster, C. R., et al., Science, 360 (2018) 1093-1096.

[3] Ming, D., et al., Science, 343 (2014) 1245267.

[4] Yamagishi, A., et al., Biological Sciences in Space, 24 (2010) 67-82.

[5] Ojha, L., et al., Nature Geosci, 8 (2015) 829-832.

[6] Mancinelli, R. L., et al., Planetary and Space Science, 48 (2000) 1093-1097.

[7] Margulis, L., et al., J. Mol. Evol., 14 (1979) 223-232.

[8] Glavin, D. P., et al., Earth and Planetary Science Letters, 185 (2001) 1-5.

[9] Navarro-Gonzalez, R., et al., Proc Natl Acad Sci U S A, 103 (2006) 16089-16094.

[10] Yamagishi, A., et al., Trans. JSASS, Aerospace Technology Japan, 16 (2018) 299-305.