The current impact rate on the regular satellites of Jupiter, Saturn, and Uranus

Context. The impact and cratering rates onto the regular satellites of the giant planets are subject to great uncertainties. Aims. We aim to compute the impact rates for objects with a diameter Di > 1 km onto the regular satellites of Jupiter, Saturn, and Uranus using dynamical simulations of the evolution of the outer Solar System coupled with the best estimates of the current population of objects beyond Neptune, and their size-frequency distribution. Methods. We analyse the last 3.5 billion years of evolution of the outer Solar System from our database of simulations and combine this with observational constraints of the population beyond Neptune to compute the flux of objects entering the Centaur region. The initial conditions of these simulations resemble the current population. We obtain an improved estimate of the impact probability of a Centaur with the satellites from enacting simulations of planetesimals flying past the satellites on hyperbolic orbits, which agree with literature precedents. Results. Our impact rate of objects Di > 1 km with Jupiter is 0.001 yr−1, which is 3–6 times lower than previous estimates. Both our impact probabilities with the satellites scaled to the giant planets and leakage rate of objects from beyond Neptune into the Centaur region are consistent with earlier literature estimates. However, our absolute impact probabilities with the giant planets are lower. We attribute this difference to whether the impact probabilities are computed over the whole age of the Solar System including planet migration, or over a shorter interval closer to the present. Conclusions. Our lower impact rate compared to earlier literature estimates is due to basing our results on the flux of objects coming in from beyond Neptune rather than relying on the current observed impact rate with Jupiter. We stress the importance of clearly stating all parameters and assumptions in future studies to enable meaningful comparisons.