New information about the complex cooling process and evolutionary history of the Moon came to light after a rock sample taken from the Apollo 17 mission was analysed recently. It was reported in Nature Communications. The rock sample troctolite 76535 was collected from the surface of the Moon during the Apollo 17 mission in 1972, and its pristine nature makes it one of the most scientifically valuable samples of the Moon. Willian Nelson, lead author of the study from the University of Hawaii at Manoa, and his colleagues used modern high-resolution analytical techniques to examine the troctolite 76535. The concentration of the phosphorus within the rock was measured and it was found that diffusion patterns preserved in mineral grains were consistent with a rapid cooling history of around 20 million years at high temperatures. What makes the new findings important is that it contrasts the previous estimates of a cooling duration of 100 million years, and therefore, supports initial rapid cooling of magmas within the lunar crust. Nelson said that the finding changes the outlook of the scientific community on how an important suite of lunar rocks formed.
“Previous reports suggest the minerals in the Apollo 17 sample were chemically homogeneous,” said Nelson in a press release. “Surprisingly, we found chemical variations within crystals of olivine and plagioclase. These heterogeneities allow us to constrain the earliest, high-temperature cooling histories of these minerals using numerical models.”
The research team proposed that a process called reactive infiltration may have formed the rock where an interaction between a melt and the rock changes its physical and chemical makeup. The study also brought to the fore the importance of using modern and more refined techniques in reanalysing samples that were examined years ago. And how our outlook on planetary evolution can be reshaped through new data.