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Non-gravitational acceleration and torque on comet 67P/Churyumov-Gerasimenko

Presentation #218.02 in the session Comets: Coma, Nucleus, Dynamics (Oral Presentation)

Published onOct 23, 2023
Non-gravitational acceleration and torque on comet 67P/Churyumov-Gerasimenko

From August 2014 to September 2016, the ESA operated the Rosetta spacecraft mission alongside with comet 67P/Churyumov-Gerasimenko (67P). The mission provided valuable long-term data on the comet’s nucleus, including its volume, mass, tensor of inertia, spatial position of the orbital trajectory, and rotational state.

The dynamical evolution of the comet can be attributed to two factors. First, gravitational forces play a role resulting from interactions with other celestial bodies in the solar system. Second, non-gravitational forces arise from the sublimation of cometary ice, causing outgassing from the nucleus into space. These outgassing processes give rise to non-gravitational acceleration (NGA) and non-gravitational torque (NGT) which affect both the trajectory and the rotational state of the comet. This includes parameters such as angular velocity and axis orientation for the rotation.

Historically, parameterizations for modeling NGA can be traced back to the work of Marsden et al. [1], while the rotating jet model (RJM) was introduced in [2]. However, these models do not account for NGT. To capture the components of NGT, a more complex shape representation is required for the cometary nucleus, as it is not simply a spherical body. Additionally, the thermophysical model is needed to quantify the sublimation activity, which depends on the solar irradiation.

In this study, we propose a parameterization for NGA and NGT resulting from the outgassing activity on the non-spherical nucleus of comet 67P. Our approach aims to establish a connection between the independent data sets of acceleration and torque. To validate our findings, we compare them with ephemeris data from ESOC flight dynamics and to [3]. We also assess the uncertainties of our NGA model in comparison to the Marsden model and the RJM. Furthermore, our parameterization closely approximates the rotational state evolution described in [4].

[1] Marsden et al. 1973, doi:10.1086/111402 [2] Sekanina 1967, BAC 18 [3] Farnocchia et al. 2021, doi:10.1016/j.icarus.2020.114276 [4] Kramer et al. 2019, doi:10.1051/0004-6361/201834349

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