Ruggieri, Alessandro (2020) Dielectric models of Ganymede and Callisto's icy crust aimed to the estimate of the performance of RIME. [Magistrali biennali]
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Radar sounding is a technique that has been expanding in the last years as a means to study the crusts of planetary bodies. In 2022 the ESA mission JUICE will be launched and, among the other instruments, it will carry the radar RIME (Radar for Icy Moon Exploration). This instrument is a 16 m antenna with a central frequency of 9 MHz and two possible bandwidths (1 and 3 MHz). In general terms, it will be used to probe the crust of Ganymede and Callisto, with an expected vertical resolution of a few tens of meters down to a few kilometers. This is possible because these bodies are mainly made up of water ice, which has a very low attenuation in the radio part of the electromagnetic spectrum. On the other hand, this is not true for liquid water. This means that, by analyzing the returned radar wave, it is possible to find an ice-water interface, if present, because such interface strongly reflects the radio signal. The consequence is that this technique allows the detection of a potential subsurface ocean, and other features, inside the icy satellites of the Solar System. The situation is more complicated since the ice of these bodies is not pure. Several chemical compounds locally change the dielectric constant and the attenuation of ice. This quantity is also affected by porosity and temperature, which change with depth. Such compounds have not uniquely identified so far. The purpose of this work is to construct dielectric models for the crust of Ganymede and Callisto, and to simulate the propagation of a radar wave having the same characteristics as those of RIME. Such models are based on reasonable assumptions about temperature profiles, porosity values, and abundances of chemical compounds taken from the literature. The most important parameter affecting these models is the presence of impurities. For this reason, recent dielectric data taken from the literature will be used to simulate the possible internal compositions of Ganymede and Callisto. Most of the literature agrees that convection is unlikely to occur inside these two satellites, therefore the temperature profile is assumed to purely conductive. The aim is to determine whether it is possible to detect specific features under the surface at a given depth. What's more, through the comparison between the models and the future RIME data, it will be possible to constrain the actual chemical composition.
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