Analytical development and numerical simulations of a space based radio-science experiment measuring the Mercury libration
- Paper number
IAC-05-A3.P.17
- Author
Mr. Gregor Pfyffer, Royal Observatory of Belgium, Belgium
- Year
2005
- Abstract
- G. Pfyffer, N. Rambaux, O. de Viron, P. Rosenblatt, T. Van Hoolst, V. DehantRoyal Observatory of Belgium, Avenue Circulaire 3, B-1180 Brussels, Belgium
In the frame of the BepiColombo and Messenger missions, the determination of the Mercury librations will enable to determine the planets core state and composition. Our work aims at understanding the physics of Mercury’s interior from the observation of its libration and first coefficients of the gravity field. To that aim, we developed the necessary theory for analyzing the impact of Mercury’s interior on these observations, and develop the necessary tools for the observation analysis. The librations are determined from observations of target positions on Mercury’s surface, and the gravity field coefficients are determined from the Doppler tracking of radio signals coming from the spacecraft around Mercury. We have determined the link between the angular observations of selected spots on Mercury’s surface and a satellite orbiting around the planet and the parameters to be determined (i.e. the libration amplitudes and phases, the obliquity angle, and the first-degree gravity field coefficients). The changes in the parameters as a function of time have been modeled and the impact of observation errors on the parameters have been determined. The impact of the possible existence of an inner core on the libration amplitudes of Mercury is determined. This is performed analytically using a simple three-layered planet, working in the frequency domain, for different percentages of light element in the core and different inner core and outer core radii (in collaboration with V. Dehant, O. de Viron, and T. Van Hoolst ). The results are then compared with the results obtained from a numerical integration computer code developed by N. Rambaux. The new model is then implemented in the analytical approach developed previously as well as in the new code. Additionally the results of further studies on the a posteriori variance on the libration amplitude are presented and in particular applied to the case of the Bepi-Colombo libration determination (specifying the orbital characteristics of the spacecraft).
- Abstract document