We propose to carry out a multi-instrument data analysis and interpretation of cassini observations that is guided by a theoretical model. Through this analysis, we investigate the source, loss,…

This is a grant awarded by the National Aeronautics and Space Administration (NASA) to the Southwest Research Institute (SwRI) to carry out data analysis and interpretation of observations from the Cassini spacecraft at Saturn. The research aims to investigate the source, loss, energization, and transport mechanisms of plasma and energetic electron populations in Saturn's magnetosphere, in order to better understand their origins and spatial distributions. The grant, valued at $208,896.20, supports NASA's Planetary Science Research Program objectives by enhancing the scientific return of the Cassini mission through multi-instrument data analysis and theoretical modeling. The grant does not have a small business set-aside designation.

We propose to carry out a multi-instrument data analysis and interpretation of cassini observations that is guided by a theoretical model. Through this analysis, we investigate the source, loss, energization, and transport mechanisms of plasma and energetic electron populations (100S of EV to 100S of KEV) to understand their origins and spatial distributions inside 1-15 RS. The expected results will increase our fundamental knowledge of how different electron populations circulate and populate saturn's magnetosphere. Early analyses of cassini data sets had provided statistical views of the radial and latitudinal distributions of warm and supra-thermal electrons at saturn and supported scenarios of magnetospehric circulation. Additionally, comparisons between particle data and diffusion theory models have showed that the adiabatic radial transport is not primarily responsible for the distributions in the region ~9-15 RS; but interaction between neutrals and electrons seems to remain one of the key processes to explain the radial, energy, and latitudinal distributions of the electron distributions inside ~12 RS. Despite the wealth of data and previous modeling, we still do not really understand why the electrons distribute as observed in the 100S of EV to ~MEV energy range. Data analyses and data-model comparison results do not provide yet all the answers to understand the main source and energization mechanisms, energy and spatial distributions, and the primary driver for the large-scale circulation of electron populations at saturn. We propose to combine data analysis and fundamental research to evaluate various processes and scenarios, and ultimately identify the dominant source, loss, energization, and transport mechanisms involved in the large-scale circulation and distribution of electron populations at saturn. We will specifically address the following key science questions: Q1: how does centrifugally driven magnetospheric diffusion transport govern the radial and spatial distributions of electron populations? Is the large-scale circulation adiabatic or non-adiabatic? What is the exact contribution of neutral environment and polar sources to the angular distributions? Q2: what are the mechanisms controlling the energy and spatial distributions inside ~12 RS? What is the relative contribution of neutrals, dust, plasma, and waves to the butterfly and pancake pitch-angle distributions? Q3: how do particle injections contribute to the energy and spatial distributions of electrons inside ~10 RS? Do they govern or only reinforce the isotropization of pitch-angle distributions? The research project requires an intensive use and analysis of particle (lemms, caps), field (MAG) and wave (rpws) measurements made by cassini spacecraft and includes theoretical modeling of physical processes to interpret the distribution and dynamical behavior of saturn's energetic electrons within a large region of the magnetosphere. For each of the key science questions, we proceed as follows: M1: perform multi-instrument analysis of cassini data sets to describe the spatial distribution of electrons and provide model constraints. M2: theoretically model source, loss, energization, and transport mechanisms and discuss their relative importance. M3: perform data/model comparisons to identify the key processes responsible for the large-scale circulation and distributions of plasma and energetic electron populations at saturn. The proposed research supports cdaps and NASA's planetary science research program objectives by enhancing the scientific return of the cassini mission. IT broadens the scientific participation in the analysis and interpretation of the data returned by this mission. IT incorporates theory and modeling that significantly increase the use of multi-instrument data sets and facilitate the interpretation of cassini observations.