There are basically three ways to do observational science. You can survey, you can do targeted observations of specific objects of interest, or you can dig through the existing data to see what can be found, lurking unnoticed, in all the exabytes already out there.

For one intern at the Johns Hopkins Applied Physics Lab, an exploration of archival data of the Moon’s Imbrium Basin led to the remarkable discovery of rocks on this volcanic plain that are made of minerals that may have been lifted up from the Lunar mantle.

Over the decades, we have painted a picture of a forming moon with low-density plagioclase floating to the lunar surface while higher density olivine and orthopyroxene should populate the lunar mantle. Lunar rocks returned to Earth by the Apollo and Luna programs were able to demonstrate that plagioclase does indeed dominate the surface, but none of the samples found evidence of the magmatic mantle. Since all of our theories on rocky planet formation have been based on a Lunar Magma Ocean model, this missing piece of the puzzle was frustrating to planetary scientists.

The now-former intern, Jordan Bretzfelder, is the first author of a new paper published in the journal Geophysical Research Letters that lays out her study of the Imbrium Basin. She used two different kinds of data to look for rocks that may have been brought to the lunar surface from the mantle during past lava flows, and she was able to identify two regions with large pieces of crustal material surrounded by those mantle-making orthopyroxene-rich materials.

According to co-author Rachel Klima: Our understanding of all planetary evolution of solid planets builds on the Lunar Magma Ocean model, which was created based on the analysis of returned lunar samples. This is the first time we have found something that could be mantle, a large area measuring multiple-scale blocks, rather than microscopic pieces.

Here is to hoping that in the not-too-distant future a new mission will be able to go gather some of these chemically interesting rocks.

More Information

JHUAPL press release 

“Identification of Potential Mantle Rocks Around the Lunar Imbrium Basin,” Jordan M. Bretzfelder et al., 2020 Oct. 29, Geophysical Research Letters