Cosmo Sikes

"Engineering Analogues of Anomalous Moon Rocks"

ABSTRACT -- The remnants of explosive volcanic eruptions can be observed across the surface of the moon and provide insight into its early volcanic history. These deposits are referred to as Dark Mantle Deposits (DMDs) due their exceptionally dark appearance and tendency to mantle the underlying topography of the lunar crust. Remote spectral data can be used to study the compositional properties of DMDs and reveals an anomalously high abundance of the mineral spinel present within the Sinus Aestuum DMD on the lunar nearside. While this implies that a unique volcanic process has occurred, which may have broader implications for lunar volcanism, its exact formation mechanism is unclear. A combination of remote sensing and experimental methods are used to study this deposit in more detail.

Remote sensing: The distribution of the SA DMD is mapped using remote data, and is observed to be, by far, the largest DMD on the moon. Because different compositions of lunar spinel have different formation mechanisms, determining the composition of spinel present within the SA DMD may help in determining what has contributed to its anomalous size and mineralogy. A previously unidentified spectral feature is detected within the UV wavelengths of the SA spinel and may indicate a Ti-rich composition. Ti-spinel is an expected crystallization product of typical lunar melts, so the presence of Ti-spinel (if confirmed) may imply that it crystallized directly from the SA DMD.

Experiments: To confirm that this spectral feature is the result of a Ti-spinel, we synthesize several Ti-bearing spinel compositions from simple combinations of reagent grade oxides. To do so, we sinter stoichiometrically proportioned powdered oxides within a 1 atm gas mixing furnace at 900°C. Gas mixtures are flowed through the furnace to set the oxygen fugacity to one log unit below the iron-wüstite buffer, which is thought to be appropriate for lunar magmatism. The resultant sintered material is powdered and compared to the remote SA spectra to infer an origin for the deposit.

SPEAKER -- Cosmo Sikes is a Ph.D. candidate at The University of Maryland, College Park, studying lunar volcanism with his advisors Jessica Sunshine and Megan Newcombe. He was awarded a NASA FINESST research grant in 2023 to fund his research. He completed his undergraduate degree in Earth Science at UC Santa Cruz, where his favorite courses included, Mineralogy, Volcanology, and Muppet Magic: Jim Henson's Art.

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