One of the unexpected discoveries of the messenger mission were the numerous vents and pyroclastic deposits indicative of explosive volcanism. In contrast to earlier formation models, which…

This $192,613.97 federal grant was awarded by the National Aeronautics and Space Administration (NASA) to The Johns Hopkins University to conduct research on the history and composition of explosive volcanic deposits on the planet Mercury. The research aims to determine when these deposits formed and analyze variations in the volatile gas fraction and magma composition across the deposits. It will leverage data from the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft mission. The research supports NASA's Discovery Data Analysis Program (DDAP) objective of enhancing scientific return from past Discovery program missions. No set-aside designation is mentioned for this grant, which has a period of performance through July 2023.

One of the unexpected discoveries of the messenger mission were the numerous vents and pyroclastic deposits indicative of explosive volcanism. In contrast to earlier formation models, which suggested that mercury had accreted with few, if any, volatile elements, explosive volcanic deposits provided evidence that mercury must have contained volatile species. Determining when in mercurian history these eruptions took place and constraining the amount and speciation of volatiles that powered them are critical to the understanding of mercury􀁁s formation and evolution. This work seeks to address two questions: 1) during what portions of mercury's history were the explosive volcanic deposits formed, and 2) is there evidence for either spatial or temporal variation in volatile gas fraction or magma composition across the deposits. This research will make use of the mascs-virs dataset for analysis of the spectral characteristics of pyroclastic deposits. We will also use the final completed mdis dataset, including the highest resolution enhanced color image mosaic and targeted images. Previous studies utilizing mascs data were performed during the early phases of the messenger mission, studying the ~39 pyroclastic deposits that had been identified at the time. These analyses identified 4 spectral subtypes with variations in overall reflectance and variations in absorption band depth at UV wavelengths. IT was suggested that differences in the subtypes types could be attributed to space weathering (age) or a varying metallic component of the deposits (composition). This proposed research would expand the earlier mascs analysis to all identified pyroclastic vents on mercury (104, identified by jozwiak ET AL., 2017), and would investigate the persistence of these previously identified spectral subclasses. The proposed research will then use the database of pyroclatic deposit mascs spectra to assess the relative ages of pyroclastic vents. Previous studies assessing the stratigraphic age of craters hosting pyroclastic vents suggest that explosive volcanic activity could have continued into relatively recent mercurian history; however, this dataset has several shortcomings. The stratigraphic method can only assess vents located in craters, and IT can only postulate on the oldest possible age of a vent, biasing the reported age distribution of vents towards older ages. The proposed research will explore how the deposit reflectance correlates with host crater degradation and with vent degradation. These data can then be used to produce a more nuanced estimate of vent age, including the possibility of explosive volcanism into recent mercury history. The proposed research will also explore variations in deposit composition by comparing pyroclastic deposit spectra with analyses of deposit volatile content. Whereas previous studies used visual approximation to identify the radial extent of pyroclastic deposits, this study will utilize the final mdis color- map products and the arcgis program to numerically assess contrast changes between the pyroclastic deposit and the background material, resulting in a reproducible dataset of deposit extent. These data will then be used to calculate volatile gas fraction at time of eruption. By analyzing variations in volatile gas fraction along with variations in deposit spectra we will investigate 1) the possibility of erosional and regolith mixing processes decreasing deposit extent through time, 2) possible correlations between eruption gas fraction and deposit composition, and 3) the possibility of heterogeneous mantle sources, this study is relevant to the ddap objective of "enhancing scientific return of discovery program missions" by combining utilizing data from two messenger instruments, mascs and mdis to drive our data analysis and science investigation.