PHYSICS AND CHEMISTRY OF UPPER ATMOSPHERES OF PLANETS FROM INFRARED OBSERVATIONS

An important goal of the study of atmospheres of planets is to provide an understanding of the relationship and interaction among phenomena occurring at different altitude and pressure regions and the effects o f external influences on these phenomena. To probe multiple pressure r egimes in general requires measurements in different spectral regions and with a wide range of spectral resolutions. This presents formidabl e technical challenges. To directly probe phenomena in the upper neutr al atmosphere (pressures <30 mbar) is particularly difficult. Much of the information on local chemistry and physics is contained in the nea r Doppler profiles of infrared molecular lines formed in these regions and spectral resolving powers lambda/DELTAlambda > 10(6) are required to adequately measure the lineshapes. The very high spectral resoluti on technique of infrared heterodyne spectroscopy capable of making suc h line measurements is briefly described. Several investigations are d escribed to illustrate the range of phenomena that can be studied and the unique physical and chemical parameters that can be retrieved. The se investigations include direct measurement of global thermospheric c irculation on Venus using Doppler shifts of nonthermal CO2 emission li nes near 10 mum; the study of Jupiter's deep interior utilizing spectr oscopy of H-2 quadrupole lines (17 and 28.2 mum) formed in the stratos phere; the evaluation of photochemical processes which determine the c omposition of Mars and the outer planets by retrieving constituent abu ndances (O3 near 9.5 mum on Mars and hydrocarbons on Jupiter and Neptu ne); and the determination of the compositional and thermal structure in Jupiter's auroral region using line profiles of auroral ethylene (C 2H4) and ethane (C2H6) emission near 10.5 and 12 mum. The value of mul tispectral and temporal observations for more comprehensive studies of atmospheric phenomena and the internal and external processes driving them are also discussed.