Dynamical evolution of C/2017 K2 PANSTARRS

Abstract

Context. The comet C/2017 K2 PANSTARRS drew attention to its activity at the time of its discovery in May 2017 when it was about 16 au from the Sun. This Oort spike comet will approach its perihelion in December 2022, and the question about its dynamical past is an important issue to explore. Aims. In order to answer the question of whether C/2017 K2 is a dynamically old or new comet it is necessary to obtain its precise osculating orbit, its original orbit, and propagate its motion backwards in time to the previous perihelion. Knowledge of the previous perihelion distance is necessary to distinguish between these two groups of the Oort spike comets. We have studied the dynamical evolution of C/2017 K2 to the previous perihelion (backward calculations for about 3–4 Myr) as well as to the future (forward calculations for about 0.033 Myr) using the swarm of virtual comets (VCs) constructed from a nominal osculating orbit of this comet which we determined here using all positional measurements available at the moment. Outside the planetary system both Galactic and stellar perturbations were taken into account. Results. We derive that C/2017 K2 is a dynamically old Oort spike comet (1/aprev = (48.7 ± 7.9) × 10−6 au−1) with the previous perihelion distance below 10 au for 97% of VCs (nominal qprev = 3.77 au). According to the present data this comet will be perturbed into a more tightly bound orbit after passing the planetary zone (1/afut = (1140.4 ± 8.0) × 10−6 au−1, qfut = 1.79336 ± 0.00006 au) provided that non-gravitational effects will not change the orbit significantly. Conclusions. C/2017 K2 has already visited our planetary zone during its previous perihelion passage. Thus, it is almost certainly a dynamically old Oort spike comet. The future orbital solution of this comet is formally very precise, however, it is much less definitive since the presented analysis is based on pre-perihelion data taken at very large heliocentric distances (23.7–14.6 au from the Sun), and this comet can experience a significant non-gravitational perturbation during the upcoming perihelion passage in 2022.