The Europa Clipper MASPEX Investigation

The MAss Spectrometer for Planetary EXploration (MASPEX) is a multi-bounce time-of-flight neutral gas mass spectrometer with unprecedented spaceborne mass resolution and sensitivity. It is capable of measuring and identifying minor and trace gases requiring mass resolution of m/Δm ~ 25,000 at abundances of parts-per-million in Europa’s exosphere. Exospheric sources of gases include exsolved, sublimed, sputtered, and radiolytically produced volatiles from Europa’s surface and interior. These gases can be used to characterize surface composition and identify volatiles outgassed from Europa’s interior. Of particular relevance in characterizing Europa’s habitability are the ratios of organic compounds such as alkanes, alkenes, alkynes, alcohols, ethers, aldehydes, amides, amines, and nitriles that undergo chemical transformations, which can be used to determine oxidation states, pH, temperature, and free energy availability of an interior ocean, perched lake, or a gas source region in the ice shell (e.g., a diapir).   This paper presents: 1) the principles and ground-calibrated performance of the MASPEX instrument that is now integrated onto the Europa Clipper spacecraft and planned to be launched in October of 2024, 2) the planned scientific investigation and its critical role in the study of Europa’s habitability, 3) the operational plans, and 4) the anticipated data products from the MASPEX investigation. The paper will also discuss the complexity of the investigation and its requisite need for the acquisition of supporting geochemical, impact fragmentation, and sputtering/radiolytic data sets that help to characterize the geochemical reaction framework and the anticipated modification of chemical species due to impacts with the instrument’s thermalizing chamber, and from radiolysis and sputtering. In the latter context we present the science team’s efforts to generate the necessary data sets, and we encourage interested scientists to contribute to this important endeavor, which is essential for the maximum success of the MASPEX investigation.