# # Program information file # PROGRAM_ID 2022A037 PROGRAM_TITLE D/H ratio in water vapor: key diagnostic to water history on Venus PROGRAM_INV1 Shohei Aoki PROGRAM_INV2 Hideo Sagawa PROGRAM_INV3 Takao Sato PROGRAM_INV4 Severine Robert PROGRAM_INV5 AnnCarine Vandaele PROGRAM_SCICAT major planets / satellites PROGRAM_ABSTRACT_BEG Deuterium/hydrogen [D/H] ratio is a key diagnostic to water history on Venus. Previous high-resolution spectroscopic measurements by ground-based telescope revealed that the D/H ratio at the deep atmosphere of Venus is 150 times larger than the terrestrial standard. This enriched deuterium on Venus has been interpreted as the results of the atmospheric escape. However, since the last observations in 1980s, no measurements of the D/H ratio in the Venus deep atmosphere have been reported. Furthermore, no spatial map of the D/H ratio has ever been investigated in the Venus deep atmosphere even though eruption of the current active volcanoes could decrease the D/H ratio on Venus by several tens of percent and produce a spatial variation of D/H geologically correlated with volcanoes. We propose high-resolution spectroscopy of 2.26-2.55 micron [K3 band] on the Venus night side with IRTF/iSHELL, which is able to measure both H2O and HDO lines simultaneously the at the Venus deep atmosphere [30-40 km altitude]. Our observations aim to investigate [1] first spatially-resolved map of D/H ratio at the lower atmosphere [below the cloud layer] and [2] long term temporal variation of D/H ratio over the past 30 years. Such a measurement of the Venus nightside was performed by iSHELL in 2019A cycle. However, the data quality was not enough to achieve the scientific goal because scattering light from dayside contaminates the nightside signal. This 2022A cycle will solve this issue because much larger night side of Venus is available. PROGRAM_ABSTRACT_END