Internal geological processes on the moon are almost non-existent. However, when hit by a space rock, its surface can change dramatically. Debris from this impact can also travel long distances and transplant material from an impact site hundreds of kilometers away, where it can remain untouched in its inert environment for billions of years.
When Apollo 17 astronauts took regolith samples at their landing site near the Serenitatis Basin, they were not only collecting rocks from the basin itself, but also from other impacts that had occurred billions of years ago. It has proven difficult to distinguish material that actually formed part of the pool from material that landed there after an impact.
The Apollo 17 astronaut Harrison Schmitt collects a soil sample in the Serenitatis Basin, his spacesuit is covered with dust.
Photo credit: NASA
A nearby impact in particular caused problems – material from the impact that created the Imbrium Basin made up the majority of the samples taken by the Apollo 17 astronauts. This basin is slightly northwest of Serenitatis and was caused by a much larger impact that is also much younger than the one that created Serenitatis.
Despite this age difference, it is difficult to distinguish rocks from one basin or another just by looking at them. One particular rock stood out, however – known as Station 8 from the geological station it was found next to, it formed as part of the Serenitatis Basin rather than its younger neighbor. It also surprised scientists with its age.
Image of the Station 8 Boulder from the Apollo 17 archives. It turns out to be the oldest sample collected by Apollo 17 astronauts.
Credit – NASA
Previous estimates of the age of the basin are between 3.8 and 3.9 billion years. However, analysis of the phosphate material in the sample returned from the boulder at Station 8 shows that its age is closer to 4.2 billion years. This would make it one of the oldest craters on the moon, which only formed about 300 million years after the moon itself.
With many manned lunar missions on the horizon, this will certainly not be the last time samples will be taken from the basin. And the techniques used by the scientists, led by a team from the Open University, are also applicable to other missions, such as the sample retrieval mission currently on its way back from Bennu. Perhaps in the future a crater older than Serenitatis will be found – but right now it looks like we already have a sample of some of the oldest possible rocks from the moon.
The Open University – Moon samples record an impact 4.2 billion years ago that may have formed one of the oldest craters on the moon
NASA – NASA opens a previously unopened Apollo sample prior to the Artemis missions
UT – NASA has a new challenge in bringing frozen samples from the moon back to Earth
Image of the moon highlighted with the two basins mentioned in the article. Serenitatis is shown with the demarcated landing area of Apollo 17.