The paths that sculpt a comet: Quantifying the sediment trajectories shaping 67P's landscapes

Abstract

Cometary surfaces exhibit striking morphological diversity, with thick, smooth deposits abruptly transitioning to exposed bedrock and cliffs. This heterogeneity reflects spatially variable sublimation driven erosion and sediment transport, yet how these processes combine to sculpt cometary surfaces remains poorly understood. Here, we investigate these dynamics on comet 67P/Churyumov-Gerasimenko by numerically modeling the ballistic trajectories of ejected particles over multiple ejection-deposition cycles. We find that the comet morphology can be explained by three fundamental dynamical regimes: collectors, where sediment trajectories converge and sediment accumulates; shadow zones, which are sheltered from incoming sediment; and ejectors, which rapidly lose sediment to space. Their spatial arrangement, controlled primarily by the nucleus shape, spin axis orientation, and rotation period, reproduces the observed distribution of surface morphologies with striking fidelity. These results demonstrate that cometary landscapes, and the evolution of their comae, arise from the coupling between ballistic sediment transport and nucleus geometry.