Asteroids Impacting the Solar System Planets and the Moon. I. Collision Rates from N-body Simulations

Abstract

Previous studies have shown a mismatch between the simulated rate of asteroids impacting the Earth and the observed rate, posing an important problem for planetary defense. Extending this analysis to other planets offers a new opportunity to examine minor body populations and impactor models. We present a unified simulation framework that estimates intrinsic $D\gtrsim10$~m impactor rates on the eight planets and the Moon. We construct size-calibrated source populations of Near Earth Objects (NEOs), Main Belt Asteroids (MBAs), Jupiter-family comets (JFCs), Centaurs, and scattering trans-Neptunian objects (TNOs), and propagate them with a 300-year $N$-body simulation. To avoid relying on black-box-like collision flags, we identify close encounters and estimate impact rates in two complementary ways: a direct count of realized impactors from object-level minimum-distance calculation and a collision expectation based on population-level impact parameter statistics. We predict over 300 years there will be $6.0^{+3.8}_{-2.7}$ impactors on Venus (all NEOs), $10.0^{+11.3}_{-4.9}$ on Earth (NEOs and JFCs), $\sim$$2981^{+481}_{-469}$ on Jupiter (mainly MBAs and JFCs), $1228^{+2759}_{-1017}$ on Saturn (mainly Centaurs), and none on the remaining planets with the $1σ$ upper limits spanning $<1.8$ (inner planets) to $<1\times10^{8}$ (outer planets; weak constraint). Jupiter uniquely receives both fast unbound impactors ($>50\, \mathrm{km\,s^{-1}}$) and slower bound ones reaching down to $\sim$$20\,\mathrm{km\,s^{-1}}$. In a companion paper, we compare our predictions with observations and test whether the gap extends across the Solar System and whether current telescopes can observe these collisions.