Establishing the absolute and relative chronology of ancient lunar events is of fundamental importance to our understanding of early Solar System history and the evolution of rocky planetary bodies. In this endeavor, the Moon has a unique quantitative role, as it is the only planetary body from which absolute and relative ages can be calibrated to one another, by way of radiometric dating of returned samples and observable surface crater densities, respectively. Yet despite the combination of returned samples and the well-preserved state of much of the lunar surface, there are many unanswered questions surrounding basin and terrane chronology.
We jointly use craters with a recognizable surface expression identified from the Lunar Orbiter Laser Altimeter (LOLA) investigation on the Lunar Reconnaissance Orbiter and those inferred from quasi-circular mass anomalies (QCMAs), considered to be buried craters, preserved in the lunar gravitational field and revealed by analyses of the gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to re-examine the ages for the formation of lunar terranes and the chronological sequence of major impact basin formation. Our results show that by using craters and QCMAs, new constraints on the ages of basins and terranes of the Moon can be established. For example, more than 40% of the large lunar impact basins that formed on the ancient Moon are confirmed to be older than 4.3 billion years old. This requires these basins to have been formed within 300 million years of the Earth-Moon system formation.
Acknowledgements: This work was conducted as part of the GRAIL mission, which was performed under contract to the Massachusetts Institute of Technology and the Jet Propulsion Laboratory, California Institute of Technology. AJE was also supported by a NASA Solar System Exploration Research Virtual Institute grant at the Southwest Research Institute. JCAH was supported by grants from the NASA Lunar Data Analysis Program and GRAIL Guest Scientist Program. We thank Katarina Miljković, William Bottke, and the GRAIL Science Team for assistance and comments.