Atmospheric chemistry on Venus — New observations and laboratory studies to progress significant unresolved issues

Franklin P. Mills, Kandis Lea Jessup, Amanda S. Brecht
2021 Bulletin of the AAS  
5 NASA Ames Research Center (MSC 245-3, Moffett Field, CA, 94035, USA, Introduction: The Venus Express-Akatsuki era has brought major advances in understanding Venus' atmosphere, but first-order unknowns remain. New observations and lab studies are needed to support and enhance recent progress in our theoretical understanding. Geographic and local time variations in composition provide important information on chemical, dynamical, and climate processes. The recent
more » ... ses. The recent development of much more capable and accurate 2D and 3D atmospheric general circulation models (AGCMs) and chemical transport models (CTMs), including data assimilation schemes, provide the tools needed to interpret high resolution 3D data sets. Systematic observations to identify both long-term climatological abundances and short-term variability are needed. Further ab initio and lab studies (e.g., spectroscopy, chemical kinetics, and state-specific probing) are needed as well to confirm the validity of postulated chemical mechanisms, clarify unknown or poorly constrained photochemical parameters, and assist with quantitative interpretation of observations. These advances will enable increased integration of multi-dimensional dynamics and chemistry and enhanced understanding of their interactions. Venus is not only our nearest neighbor. It is also our nearest laboratory for understanding the diversity of atmospheric chemistry that will be found on exoplanets and a key comparative benchmark for understanding the divergent evolutionary paths of terrestrial-like planets. Scientific Issues and Challenges: Venus' bulk atmospheric composition (96.5% CO2, 3.5% N2) and the identity of many of its most abundant reservoir species (SO2, H2SO4, HCl, H2O) have been known for decades (Marcq et al., 2018) . Its major chemical processes are even believed known -CO2 photolysis and CO oxidation; sulfur oxidation, condensation to form H2SO4 clouds, and evaporation; and polymerization of sulfur to form polysulfur (Marcq et al., 2018 ). Yet beneath this veneer of top-level "knowledge" lie significant and important uncertainties and unknowns (Marcq et al., 2018) : • What chemical mechanisms quantitatively maintain the photochemical stability of CO2? • What chemical/aerosol species absorb sufficient UV-blue light to account for around 50% of the solar radiation absorbed by Venus' atmosphere? • How, how much, and where do the atmosphere and surface interact? • What are the implications for and consequences of active volcanism on Venus? New, systematically planned and acquired observations are critical for answering these questions. Integration of increasingly complex chemical mechanisms with circulation models that are increasing markedly in sophistication, resolution, and accuracy is also critical because observed species distributions reflect the complex interactions of dynamics, chemistry, and radiation. Underpinning the advances from new observations and integrated models are lab studies identifying and validating postulated chemical mechanisms. Advances in all of these areas are needed to further not only our understanding of Venus' atmospheric chemistry, but also to interpret observations of terrestrial-like exoplanets, including exo-Venuses, and to advance comparative studies of Mars, Earth, and Venus and understand their apparent evolutionary divergence. Atmospheric chemistry is complex because of both its interaction with transport and its sensitivity to species whose relative abundances may be a few parts per billion (ppb) or parts per
doi:10.3847/25c2cfeb.7a0b2f82 fatcat:meaplfurtjcwlfq4knzyyordxu