Geometrical model of jets in cometary comae

Abstract

Cometary comae frequently exhibit various formations such as jets, fans, and shells, which can provide crucial insights into the nuclear rotation parameters and the presence of active regions on cometary nuclei. To accurately interpret the visible shape of these jets, a geometric model has been developed. This model considers several factors, including the position of the comet nucleus’s axis of rotation, the location of active areas on the comet’s surface, the angular size of the emission cone, and the relative positions of the Earth, the Sun, and the comet. Utilizing this model, it is possible to track the evolution of the jets over extended periods, enhancing the precision of the model parameters estimation through its simplification. Application of the geometrical model is demonstrated in determining the rotational parameters of the nucleus of comet C/2017 K2 (PANSTARRS). The coordinates for the positive pole of the rotational axis of the comet’s nucleus are: right ascension $\alpha =70°\pm 15°$, declination $\delta =-45°\pm 6°$, and the rotation period is 166.50 ± 0.02 h. The shape of the jet feature is consistent with an active area located at that latitude $\varphi =+45°\pm 6°$. The mean velocity of the dust particles is calculated to be 0.23 ± 0.03 km/s.