New analyzes of old samples reveal the evolution of the Moon

New analyzes of old samples reveal the evolution of the Moon

New and more sophisticated analyzes of a rock sample collected in 1972 on the moon by the Apollo 17 mission have revealed new information on the evolutionary history of our satellite. The diffusion patterns preserved in mineral grains were consistent with a rapid cooling history of no more than 20 million years at elevated temperatures. The discovery challenges previous estimates of a cooling duration of 100 million years and supports the rapid initial cooling of magmas within the lunar crust.

William Nelson, lead author of the study and graduate student of science of the Earth at the UH Manoa School of Ocean and Earth Science and Technology (SOEST), and co-authors used a specialized electronic microprobe to perform high-resolution analysis of troctolite 76535.

“Previous reports suggested that minerals in the Apollo 17 sample were chemically homogeneous, ”Nelson explained but“ surprisingly, we found chemical variations within olivine and plagioclase crystals. These heterogeneities allow us to limit the earliest reports of high-temperature cooling of these minerals using numerical models ".

SOEST researchers used UH High-Performance Computing facilities, Mana, to consider the effects of a variety of computer-simulated cooling pathways, well over 5 million chemical diffusion patterns. "The simulations revealed that these heterogeneities could only survive for a relatively short period of time at elevated temperatures," Nelson said.

To reconcile high-temperature cooling rates with the generally accepted view of how these rocks formed, the team of researchers proposed that perhaps this type of rock formed from a process called infiltration reactive in which a melt interacts with the rock, changing its chemical and physical composition.

The study also demonstrates how important it is to re-examine previously analyzed samples using modern techniques and how quickly new data can reshape our understanding of planetary evolution. To better understand the observed chemical heterogeneity, the team is currently studying how quickly phosphorus can diffuse into olivine crystals. Furthermore, they are looking for similar heterogeneities in other Apollo samples.

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