We propose to conduct a four-year study to improve the understanding of subsurface hydrogen and chlorine distributions throughout Mars Science Laboratory (MSL) Curiositys traverse in Gale Crater by conducting surface operations experiments with the Dynamic Albedo of Neutrons (DAN) instrument and by modeling DAN data using geochemical models. The importance of accounting for high absorption cross section elements like chlorine on Mars (and gadolinium or samarium on the Moon) was first demonstrated using planetary neutron data from orbit (Dietz et al., 2008; Feldman et al., 1998). The importance of properly accounting for chlorine and iron abundances when interpreting DAN measurements on Mars has been thoroughly demonstrated through modeling and subsequent analyses of Curiosity surface data (Hardgrove et al., 2011; Hardgrove et al., 2014). Initial results from DAN have shown significant variability in neutron counts throughout the mission, yet the observed local geology (as determined through images or geochemical data) and the effects of high neutron absorption cross-section elements like chlorine have not been properly accounted for when interpreting DAN data (Mitrofanov et al. 2014; Litvak et al. 2014). In addition, the appropriate surface data have not yet been acquired for fully characterizing DANs response to homogeneous materials of known composition (as determined by Curiositys other geochemical instruments). This study, therefore, will focus on three primary tasks: (1) Improving DAN subsurface models at specific sites using additional surface geochemical data from other instruments on Curiosity; (2) Using DAN models from specific sites with known geochemistry to interpret DAN data acquired through Curiositys traverse (from landing to present), in order to better constrain the subsurface hydrogen abundance in places where other geochemical data were not acquired; (3) Modeling the effects of variable rock abundance, density, and subsurface temperature distributions on DAN measurements, and (4) Participating in MSL surface operations to acquire key measurements with DAN at contact science and mid-drive targets of opportunity. This investigation will address several MSL mission-level science objectives, and those specifically desired by the MSL Participating Scientist Program (PSP). This proposal will result in Characterization of geological features contributing to deciphering geological history and the processes that have formed or modified bedrock and regolith, with emphasis on the role of water as well as in Characterization of the local environment, including . . . the near-surface distribution of hydrogen. The MSL PSP states that proposals are specifically desired to Enhance the science return from the DAN instrument. The proposed work is also relevant to the major goals of initiating and preparing for Mars Sample Return and caching. Understanding how to infer shallow subsurface compositions and habitability potential from surface observations can significantly influence future rover sampling and caching decisions. The DAN instrument on Curiosity is currently our only geophysical (shallow subsurface) instrument on the surface of Mars, and it will be critical to understand these data to inform future sampling decisions. This proposal will also provide new data products to the planetary science community, and would provide significant support for an early career researcher.
|Effective start/end date||4/1/16 → 10/31/19|
- National Aeronautics Space Administration (NASA): $511,457.00