[BBG02-01] 生命兆候顕微鏡による火星での生命兆候探査
キーワード：蛍光顕微鏡、アストロバイオロジー
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.
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.