Modeling Radar Wave Propagation Through Comet 67P / Churyumov-Gerasimenko

Abstract:

The Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) onboard the Rosetta mission, as well as future cometary mission concepts, are planned to explore the inner structure of comets to complement our knowledge on the evolution of these small bodies that is currently only driven by surficial remote sensing measurements. An essential step in understanding the performance and the science return of current and future sounding experiments is an accurate understanding of the dielectric properties of comets and how they translate to the different physical, chemical and structural hypotheses of these bodies. To help constrain the ambiguities associated with this wide parametric space, we build eight parametric 3D dielectric models of the comet nucleus representing different structural and physical formation hypotheses, and we simulated the propagation of radar waves through each nucleus model using the finite difference time domain (FDTD) method. We extrapolated the shape model from the first Rosetta Navigation Camera images, while the different internal structures of each model are representative of existing theories of comet nuclei structures. The complex dielectric constants used in our models have been generated using mixing laws for a porous mixture of ice and meteoritic dust. Our simulations were performed at a lower frequency with respect to the central frequency of the CONSERT instrument due to computational memory limitations. The lower resolution obtained will still provide a sufficient and close approximation of the final experiment, given that the dielectric properties of the nucleus’ materials are non-dispersive. Our results suggest that each model of the comet nucleus’ interior structure produces a different radar signature in both the transmitted and reflected signals. In particular we note that scattering from inner-structure complexity compromises the visibility of the comet backside. Our simulation suggests that we can discern the different formation hypotheses with their associated internal structures for Comet 67P using the CONSERT experiment. Our results will support the CONSERT data interpretations to determine whether Comet 67P was generated by the aggregation of icy rubble, whether it presents a layered inner structure, and also whether it is a two-body system.