Age Estimation of Individual Lunar Simple Craters Using the Topography Degradation Model

Abstract

Crater statistics is the canonical method used to estimate model ages of planetary surfaces, frequently applied on ejecta facies of individual craters to estimate their formation ages. Model ages of simple craters are critical information in planetary geology, but the applicability of crater statistics for ejecta deposits of simple craters is usually hindered by small counting areas and/or limited number of usable craters, also hampered by unconstrained effects of heterogeneous target properties and various forms of background secondaries. This difficulty is especially pronounced for relatively old and small simple craters. On the other hand, topographic degradation of simple craters on the Moon can be modeled using the diffusive equation. Assuming an ideal original topographic profile for pristine simple craters, topographic degradation states of simple craters were used to estimate their formation ages, but earlier endeavors were not calibrated and the effect of large topographic variations of pristine simple craters lacks constraint. Here, we developed this method by updating topographic profiles for pristine lunar simple craters. Variations of initial topographic profiles are considered in the model construction, yielding an uncertainty of less than ∼165 Ma for the derived model ages of craters larger than 400 m. The first-order reliability of this method is verified by applying it to craters with isotopic ages constrained by lunar samples, and the derived degradation ages are also broadly consistent with model ages derived from crater statistics. However, this method is less suitable for craters smaller than 400 m due to their much larger initial topographic variations.