Re-examining the main asteroid belt as the primary source of ancient lunar craters

Abstract

It has been hypothesized that the impactors that created the majority of the observable craters on the ancient lunar highlands were derived from the main asteroid belt in such a way that preserved their size-frequency distribution. A more limited version of this hypothesis, dubbed the E-belt hypothesis, postulates that a destabilized contiguous inner extension of the main asteroid belt produced a bombardment limited to those craters younger than Nectaris basin. We investigate these hypotheses with a Monte Carlo code called the Cratered Terrain Evolution Model (CTEM). We find that matching the observed number of lunar highlands craters with Dc~100 km requires that the total number of impacting asteroids with Di>10 km be no fewer than 4x10-6 km-2. However, this required mass of impactors has <1% chance of producing only a single basin larger than the ~1200 km Imbrium basin; instead, these simulations are likely to produce more large basins than are observed on the Moon. This difficulty in reproducing the lunar highlands cratering record with a main asteroid belt SFD arises because the main belt is relatively abundant in the objects that produce these "megabasins" that are larger than Imbrium. We also find that the main asteroid belt SFD has <16% chance of producing Nectarian densities of Dc>64 km craters while not producing a crater larger than Imbrium, as required by the E-belt hypothesis. These results suggest that the lunar highlands were unlikely to have been bombarded by a population whose size-frequency distribution resembles that of the currently observed main asteroid belt. We suggest that the population of impactors that cratered the lunar highlands had a somewhat similar size-frequency distribution as the modern main asteroid belt, but had a smaller ratio of objects capable of producing megabasins compared to objects capable of producing ~100 km craters.

arXiv comment77 pages, 18 figures, Submitted to Icarus: January 10, 2014. Revised: August 21, 2014

References in corpus (15)

• Catastrophic disruptions revisited
• Asteroids Were Born Big
• Main Belt Asteroids with WISE/NEOWISE I: Preliminary Albedos and Diameters
• The origin of planetary impactors in the inner solar system
• Orbital Evolution of Planets Embedded in a Planetesimal Disk
• A Sawtooth-like Timeline for the First Billion Year of Lunar Bombardment
• Evidence from the asteroid belt for a violent past evolution of Jupiter's orbit
• The variability of crater identification among expert and community crater analysts
• Steady-State Size Distributions for Collisional Populations: Analytical Solution with Size-Dependent Strength
• Dynamical erosion of the asteroid belt and implications for large impacts in the inner solar system
• Constructing the secular architecture of the solar system II: The terrestrial planets
• On the Migration of Jupiter and Saturn: Constraints from Linear Models of Secular Resonant Coupling with the Terrestrial Planets
• Secular resonance sweeping of the main asteroid belt during planet migration
• The Collisional Divot in the Kuiper belt Size Distribution
• NEOWISE Studies of Asteroids with Sloan Photometry: Preliminary Results

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• Late veneer and late accretion to the terrestrial planets
• Impact bombardment chronology of the terrestrial planets from 4.5 Ga to 3.5 Ga
• Early Bombardment of the Moon: Connecting the Lunar Crater Record to the Terrestrial Planet Formation
• An analytical model of crater count equilibrium
• The role of breccia lenses in regolith generation from the formation of small, simple craters: Application to the Apollo 15 landing site
• Radio-flaring Ultracool Dwarf Population Synthesis
• Formation of Lunar Basins from Impacts of Leftover Planetesimals
• Number of near-Earth objects and formation of lunar craters over the last billion years
• Depths of Copernican craters on lunar maria and highlands