Uniformity of Crater Equilibrium in Ceres’s Densely Cratered Regions

Session: Geomorphology and Surface Processes Across the Solar System

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Abstract:

Ceres is a heavily cratered dwarf planet preserving evidence of long-term impact history.  Early in its evolution, its surface accumulated craters steadily due to frequent bombardment. Over time, newer craters began to erase older ones, eventually leading to a balance between crater formation and degradation, a state known as crater equilibrium. Prior studies have shown mixed results on whether equilibrium behaves uniformly across planetary surfaces. Hartmann [1] observed consistency across multiple Solar System objects, while Xiao and Werner [2] reported regional variation on the Moon. This study evaluates whether crater equilibrium is uniform across several densely cratered regions on Ceres.

We assessed crater equilibrium using crater size-frequency distributions (CSFDs), which show the cumulative number of craters above a given size per unit area, providing a statistical profile of impact history. They distinguish between areas still accumulating craters from those in equilibrium.

Three quadrangles (Ac-2, Ac-8, Ac-12) were selected for their high crater density and uniform terrain. Manual crater counts were performed in QGIS using high-resolution Dawn Framing Camera images. Crater diameters were measured using rim curvature and shadow geometry, then logarithmically binned to construct CSFDs. Plotting the results in log–log space distinguishes the production regime's steep slope from the flatter equilibrium regime. We focused on craters between 0.4 and 10 km in diameter to capture both behaviors.

To compare the CSFDs more rigorously, we extended the analytical model proposed by Hirabayashi et al. [3, 4], which simulates crater accumulation and degradation. It links these processes through a set of fitted parameters. The production slope was derived by fitting the large-crater portion to the Neukum–Hiesinger [5, 6] production function for Ceres. The equilibrium regime was determined from the small-crater range, where slope flattening indicated degradation effects.

All three regions showed consistent equilibrium behavior despite surface age differences ranging from 1.4 to 3.1 Gyr. This supports uniform equilibrium states on Ceres’ heavily cratered terrains, aligning with Hartmann’s findings. While localized deviations are possible, such detail lies beyond the scope of this study.

References: [1] Hartmann W.K. (1984) Icarus 60. [2] Xiao, Z. & Werner, S.C. (2015) JGR: Planets 120. [3] Hirabayashi, M. et al. (2017) Icarus 289. [4] Hirabayashi, M. et al. (2024) Planet. Sci. J. 5 250. [5] Neukum, G. et al. (2001) Space Sci. Rev 96. [6] Hiesinger, H. et al. (2016) Science 353.