Glass-type hydrogen and deuterium absorption cells developed for d/h ratio measurements in the martian atmosphere

Hydrogen and deuterium absorption cells of a new glass type have been developed for the DyH ratio measurements on the Japanese Mars mission PLANET-B. The H/D cells work as narrow-band rejection filters for the H/D Lyman-a line, respectively, when the H or D atoms are produced at a heated filament inside the cells. The absorption profiles of the cells were successfully measured with a highresolution vacuum ultraviolet spectrometer with a wavelength resolution of 6.6 3 1024 nm. The derived optical thickness was found to be ∼7 and ∼14 for the hydrogen and deuterium cells, respectively. It was also found that the derived temperature of atomic gas ranges between the temperature of the cell wall and that of the heated filament, and it increases with increasing filament temperature. The measured profiles showed that the absorption efficiencies of the developed absorption cells are sufficient to observe the DyH ratios of the Martian atmosphere.