One of the significant scientific outcomes from the lunar sample return missions (Apollo, Luna, Chang'e) has been the establishment of a chronology model that allows deducing the age of surfaces based on the observed crater density.
This model is currently the only available tool for dating the surfaces of the Solar System, thus specifying the timing of major events responsible for their geological evolution. However, most chronology models assume a homogeneous cratering rate across the entire lunar surface.
Asymmetry in the lunar cratering rate. The black and yellow dots symbolize terrains sampled by the Apollo (A), Luna (L), and Chang'e-5 (CE) missions.
© A. Lagain et al. (2024)
Nonetheless, the synchronicity of the Moon's orbit around Earth and the orbital distribution of impactors challenge the hypothesis of a homogeneous lunar impact flux. What is the intensity and implications of an impact flux heterogeneity on the measurement of the lunar surfaces' ages? This is exactly what an international research team, involving the CNRS Earth & Universe, has just determined.
The scientists discovered that the cratering rate on the Moon varies by a factor of ~1.8 between different regions. The consequence for interpreting lunar samples? The regions where these rocks originated would not have recorded the same impact rate, and therefore, the chronology systems of the Solar System bodies are found to be flawed. The researchers then used this variation in the cratering rate to recalibrate the lunar chronology.
This new model alters the age of lunar surfaces deduced from crater counts by up to 30% over decades. As a result, our understanding of the timing of the Moon's geological activity might be revised, as well as the chronologies of other planetary bodies such as Mercury and Mars, which are calibrated against the Moon's timeline. Finally, future lunar sample return missions such as Artemis or Chang'e-6 will further refine this chronology for the oldest periods, more than 3.5 billion years ago.
References:
Anthony Lagain, Hadrien A.R. Devillepoix, Pierre Vernazza, Darrel Robertson, Mikael Granvik, Petr Pokorny, Anthony Ozerov, Patrick M. Shober, Laurent Jorda, Konstantinos Servis, John H. Fairweather, Yoann Quesnel, Gretchen K. Benedix
Recalibration of the lunar chronology due to spatial cratering-rate variability
Icarus, Volume 411, 2024.