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Geological information is essential for a country like Japan, located at a tectonically active area, to ensure a safe and secure society. The Geological Survey of Japan gathers, compiles, and provides geological information and promotes its wider use. We also develop technologies to overcome various difficulties related to global environment protection, exploration of minerals and energy resources, and natural disaster mitigation, and coordinate international cooperation as a national representative.
In 2020, AIST researchers estimated the microbially mediated methane consumption rate by chemical and microbiological analyses coupled with stable isotope tracer experiments of sediments collected from the seafloor off Sakata City, Yamagata Prefecture, where methane hydrates are distributed. They also discovered that in the redox transition zone below the seafloor, methane-oxidizing microorganisms that require oxygen for growth (aerobic methanotrophs) and those that do not (anaerobic methanotrophs) are metabolically active and consume methane. These findings contribute to an accurate understanding of the seafloor budget of methane.
Methane consumption rate was estimated by geochemical and microbiological analyses and incubation experiments of subseafloor sediments. *Figure modified from Miyajima et al. (2024)
Researchers at AIST, in collaboration with Tohoku University, the Japan Atomic Energy Agency, the University of Tokyo, Kyushu University, and others, conducted a direct comparison of remote-sensed data of the Cb-type asteroid Ryugu’s surface observed by the Asteroid Explorer Hayabusa2 and lab-measured data using Ryugu samples brought back to the Earth by Hayabusa2 spacecraft without exposure to the Earth's atmosphere. The remote-sensed and lab-measured reflectance spectra of Ryugu are quite similar, however, a clear difference is the OH absorption band depth: the OH band of remote-sensed spectra is more than half weaker than that of lab-measured spectra. To clarify what causes that difference, we performed lab experiments and data comparisons using primitive carbonaceous chondrites similar to Ryugu. Then we revealed that the most likely cause is that the surface of Ryugu, about 1/100 mm in depth, has been affected by space weathering, alteration caused by exposure to cosmic rays and cosmic dusts, resulting in partial dehydration and the OH band weakening. Our result has been enabled for the first time by the combination of remote sensing of asteroid Ryugu and laboratory measurements using collected samples by Hayabusa2, and suggests the importance of sample return missions playing an important role in planetary science.
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