Ephemeris Reconstruction for Comet 67P/Churyumov-Gerasimenko During Rosetta Proximity Phase from Radiometric Data Analysis

This study provides a continuous ephemeris reconstruction for comet 67P/Churyumov-Gerasimenko by reanalyzing Rosetta radiometric measurements and Earth-based astrometry. Given the comet-to-spacecraft relative trajectory provided by the navigation team, these measurements were used to estimate the comet state and some critical physical parameters, most notably the non-gravita-tional accelerations induced by the outgassing of surface volatiles, for which different models were tested and compared. The reference reconstructed ephemeris, which uses a stochastic acceleration model, has position uncertainties below 10 km, 30 km, and 80 km in the orbital radial, tangential, and normal directions for the whole duration of the Rosetta proximity phase (from July 2014 and October 2016). Furthermore, the solution can fit ground-based astrometry between March 2010 and July 2018, covering a complete heliocentric orbit of 67P. The orbital radial and normal components dominate the estimated comet’s non-gravitational accelerations, reaching peak values of (1.28 ± 0.17)∙10-8 m/s2 and (0.52 ± 0.20)∙10-8 m/s2, respectively 15 days and 24 days after perihelion. Furthermore, the acceleration magnitude is shown to have a steep dependence on the comet’s heliocentric distance (𝑁𝐺𝐴~𝑟−6) and shows asymmetries in the pre- and post- perihelion activities. The estimated acceleration components, which are agnostic due to the limited physical assumptions, could be used as a constraint for future investigations involving high-fidelity thermophysical models of the comet’s surface.