# # Program information file # PROGRAM_ID 2024B085 PROGRAM_TITLE Sulfur monoxide in the Venusian atmosphere: Aiming for the first-time detection in the mid-infrared region PROGRAM_INV1 Hideo Sagawa PROGRAM_INV2 Therese Encrenaz PROGRAM_INV3 Thomas Greathouse PROGRAM_INV4 Shohei Aoki PROGRAM_INV5 Tatsuro Iwanaka PROGRAM_SCICAT major planets / satellites PROGRAM_ABSTRACT_BEG One of the main characteristics of Venus is the relatively high content of sulfur-bearing species in the atmosphere. This suggests either a continuous supply of sulfur to the atmosphere from volcanic activity or the absence of an ocean to which the sulfur dissolves, which are important for understanding the evolution of Venus. More to the point, sulfur dioxide [SO2] in the Venusian atmosphere is well known as the primary material of the clouds, which control the amount of incident solar radiation. Despite the importance, the distribution of SO2 in the Venusian atmosphere remains much of a mystery. In particular, the rapid decrease in its abundance in the upper cloud layer has not yet been properly reproduced by any atmospheric chemistry model. In short, our understanding of sulfur-related chemistry, the most important atmospheric chemistry in Venus, is still incomplete. In order to improve this situation, this proposed observation focuses on sulfur monoxide [SO], which has been particularly poorly observed among major sulfur-bearing species in Venus. SO is produced from SO2 and is highly sensitive to the sulfur chemistry, therefore it can be used as test species to assess our current knowledge on the Venusian sulfur chemistry. This TEXES observation will aim at the first-time detection of SO using the mid-infrared wavelength, and try to constrain its diurnal variation in the upper cloud layer [altitude around 67 km] with a very high sensitivity [5 ppbv-level]. Even constraining an upper limit will provide valuable insights: if even the SO-rich dayside is constrained to be present at less than 5 ppbv, then there should be some hidden chemical reaction process that inhibits the upward transport of SO2 [source of SO] in the cloud layer. PROGRAM_ABSTRACT_END