Lunar samples record impact 4.2 billion years ago that formed one of the oldest craters on the Moon

Researchers provide the first sample-based evidence for the age of the Serenitatis Basin

TORONTO, ON, June 9, 2021 – An international team of researchers from the UK, Sweden and Australia, Canada, including Dr. Kim Tait, Teck Endowed Chair of Mineralogy from the Royal Ontario Museum (ROM), have provided the first sample-based evidence for the age of the Serenitatis Basin, one of the Moon’s oldest craters.

The formation and ages of the lunar basins and craters, created during large collisional impact events during the roughly first 500 million years of the Solar System’s history, have fascinated scientists since the earliest observations of the Moon.

Determining accurate formation ages of impact craters on the Moon is of fundamental importance for ascribing ages to “un-sampled” planetary surfaces across the inner Solar System, such as those on Mars, Mercury and Venus.

Since the earliest observations, the Serenitatis Basin has been thought to be one of the oldest large craters on the near side of the Moon. To determine the exact ages of lunar craters, one of the aims of the Apollo missions was to obtain rock samples, which were believed to have formed during the massive impact events that created such large basins. In particular, the Apollo 17 mission aimed at collecting Serenitatis-related samples.

Previous studies have shown, however, that most of Apollo 17 rock samples were likely created in a much younger impact event, associated with the formation of known as the Imbrium basin. Imbrium ejecta is dispersed across much of the nearside of the Moon, which has obscured the determination of the true age of the Serenitatis Basin – indicating that it could be approximately 3.8 to 3.9 billion years old.

The newest findings have now provided a more accurate reflection of the Serenitatis Basin’s timeline, by studying an exceptional sample from the so-called “Station 8 boulder” that suggests the Serenitatis Basin was actually created 4.2 billion years ago – 300 million years earlier than initially thought.

Another important finding from this study is that Station 8 boulder also recorded a very young impact event, which occurred about 500 million years ago. Such young impacts are rarely recorded in lunar samples and this one was overlooked by previous studies. Adopting an inter-disciplinary collaborative approach, the team set about integrating the laboratory results with the lunar remote sensing dataset and impact crater modelling, which revealed that this young impact could be linked with the formation of Dawes crater, located 140 km away from the Apollo 17 landing site.

The Apollo 17 sample used in this study was provided by NASA, and the new discovery has been realised by a team led from The Open University and involving researchers from the University of Portsmouth (UK), Royal Ontario Museum, University of Toronto and Université de Sherbrooke (Canada), Swedish Museum of Natural History (Sweden), and Curtin University (Australia).

The study was initiated by Dr. Ana Černok, recently a Hatch Postdoctoral Fellow at the ROM, when she was a Marie Curie Fellow at The Open University (2016-2018) and where she is currently an Honorary Associate.  

“We looked at this fascinating sample for a long time and tried to disentangle its complex radiogenic ages,” says Dr. Černok. “It has been difficult to establish the exact link of the samples to the Serenitatis Basin ever since the Apollo 17 collection was brought back, because it was not easy to discern between samples formed by the Imbrium event and those formed by Serenitatis.”

Dr. Lee White, formerly a Hatch Postdoctoral Fellow at the ROM, is currently a Post Doctoral Research Assistant at The Open University, adds: “The new study highlights the importance of careful sample curation and repeated analysis of well-characterised samples using the latest analytical techniques and methods. In addition, it reveals the immense potential of studying materials at the nanoscale, which can be of great importance for the future sample return missions, such as those from the asteroid Bennu or from Mars.’’

Professor Mahesh Anand is the Professor of Planetary Science and Exploration at The Open University and the institution’s Principal Investigator of Apollo samples. “This project focused on studying phosphate minerals in lunar samples, which simultaneously carry valuable information on water abundance and radiogenic ages,” he explains. “Based on the novel structural observations of phosphates at sub-micron scale, combined with very precise age determinations of the exact same phosphate mineral grains, we were able to correlate the 4.2-billion-year age to the massive impact event that likely formed the Serenitatis Basin.”

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Research Paper: Lunar samples record an impact 4.2 billion years ago that may have formed the Serenitatis Basin, published in Communications Earth & Environment.

DOI 10.1038/s43247-021-00181-z

Image Caption: Apollo 17 Panorama, Station 8. The panorama was collected by Harrison H. "Jack" Schmitt at Station 8. Eugene Andrew Cernan is near the rover picking up the Traverse Gravimeter to stow it on the rover. The object in the foreground is the scoop Jack has planted while he takes the panorama photographs. The panorama is made from the frame set AS17-142-21726 to 21745.

Credit: NASA, USGS Astrogeology Science Center

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