The objective of Dr. Nancy Chanover's project is to study the balance between reflected solar radiation at Saturn's cloud decks and emitted thermal radiation from Saturn's interior. Using a technique of spatially resolved spectroscopy, this research team will obtain a unique data set that, when coupled with radiative transfer and spectral synthesis modeling, will accomplish the following measurement objectives: a) determine the spatial and temporal variation of Saturn's cloud opacity, and b) determine the spatial and temporal variation of Saturn's chemical composition. These measurements will enhance our understanding of Saturn's atmospheric processes, including its dynamics, chemical composition, and radiative transfer.
The medium- and high-resolution infrared spectrometers at the Infrared Telescope Facility 3.0 meter telescope will be used to acquire spectra of Saturn between 2.5-5.4 m, which is a wavelength region particularly sensitive to cloud opacity and scattering properties. Saturn's "cold spots," which may control the radiative transfer through Saturn's atmosphere in a manner analogous to Jupiter's 5-m "hot spots", will be studied as a function of latitude and slant path geometry. This will elucidate the detailed vertical structure of the atmosphere and the role of the cold, dark regions in controlling the thermal emission from the planet. The spatial and temporal variations of ammonia, phosphine, and ethane on Saturn will be examined as a means of understanding Saturn's atmospheric dynamics. Phosphine (PH3) is a disequilibrium species, thus any spatial variation in PH3 may be linked to variations in upwelling from the deep atmosphere, whereas variations in ammonia would be associated with spatial variations in cloud formation. Center-to-limb studies of ethane, a stratospheric molecule, will differ from those of ammonia, which is found in Saturn's troposphere. Ethane can be detected near 3 mm, and will provide an important constraint for understanding Saturn's atmospheric vertical structure. While Saturn's reflectivity variations as a function of latitude are more subtle than those of Jupiter, the dynamics driving the circulation of the two planets may be similar. Thus, a study of the latitudinal variation in Saturn's infrared spectrum is relevant to the understanding of the energy balance of Saturn's atmosphere. All data will be modeled using both center-to-limb analyses and spectral synthesis methods. With these two approaches, the goal is to develop a unified model of Saturn's atmospheric structure that places aerosol layers at the appropriate vertical levels, characterizes cloud and haze opacities and optical properties, derives mixing ratios for ammonia, phosphine, and ethane, and quantifies the temporal and spatial variations of the above quantities. This study will make unique contributions to our understanding of Saturn's atmosphere. By interpreting observations of Saturn's reflected and thermally emitted radiation using a self-consistent modeling approach, the team will develop a comprehensive description of the energy balance in Saturn's atmosphere. Prior studies will be improved by using an observational approach that can exploit the unique attributes of spatially-resolved spectroscopy. The observations will overlap the spectral coverage of Cassini's Visible and Infrared Mapping Spectrometer (VIMS), and will complement the high phase angle spacecraft data taken contemporaneously with the ground-based data. They will also probe deeper pressure levels than Cassini's Composite Infrared Spectrograph (CIRS), and therefore will provide an essential component of molecular mixing ratio studies.
This work is interdisciplinary and promotes synergy between the analysis of reflected sunlight that has been conducted at New Mexico State University (NMSU) to date and the thermal infrared work in which the Co-Investigators are experts. This program will promote teaching and training through practical research by involving several NMSU students and giving them opportunities to participate in all aspects of the research. In addition, it will broaden the participation of women and ethnic minorities, both underrepresented demographics in science and engineering fields. ***
