Development of the Life-signature Detection Microscope (LDM) for in situ imaging of organic compounds including living cells on Mars
Abstract
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 10$ ^{6}$ 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 mm$ ^{3}$ and detects less than 10$ ^{4}$ 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. We have been developing the breadboard model (BBM) of LDM, which is composed of 4 parts: a sample chamber, a light source, a microscope, and a camera. The sample chamber includes sample holders for soil, pigment solution tanks, and membrane filter units which are used for the concentration of particles. Following the addition of the pigment solutions to the sample holders and filter units, the bottom of them are observed by the microscope and digital images are obtained. As the light source, a blue laser diode for the excitation of the pigments and LEDs for bright field observation are equipped. Here we will report the current status of the BBM. 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.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1956Y