Our objective is to improve interpretation of in situ and remote-sensing data of mercury. We will use updated exosphere and spectrophotometric models that incorporate new data from our proposed…

This federal contract award, valued at $1,254,926.35, was granted to The Trustees of Columbia University in the City of New York, operating as Columbia University, by the National Aeronautics and Space Administration (NASA). The objective of the contract is to improve the interpretation of in situ and remote-sensing data of the planet Mercury by conducting laboratory simulations of solar wind ion irradiation on Mercury's regolith surface. The research aims to provide quantitative data on the sputter yield and spectral changes resulting from this ion irradiation, which will be incorporated into updated exosphere and spectrophotometric models. This work will address key planetary science questions related to the formation of Mercury's sodium exosphere and the alteration of its spectrophotometric properties due to solar wind ion interactions. The contract does not have a set-aside designation, and the work is scheduled for completion by May 13, 2023.

Our objective is to improve interpretation of in situ and remote-sensing data of mercury. We will use updated exosphere and spectrophotometric models that incorporate new data from our proposed laboratory simulations of solar wind ION irradiation of mercury's regolith surface. Current models, to simulate mercury's exosphere and to analyze spectrophotometric data of the surface, make questionable assumptions about the sputter yield and spectral changes from ION irradiation. This is due to the lack of experimental data for regolith-like loose powders. Our laboratory studies will be the most realistic simulations to date for the effects of ION irradiation on regolith-like loose powders and will provide quantitative data for the corresponding sputter yield and spectral changes. We will incorporate these data into our exosphere and spectrophotometric models and reinterpret archival data of mercury. Specific planetary science questions that we will address include: (1) what fraction of the NA exosphere of mercury is formed by solar wind ions? (2) is there a systematic difference between sputtering in mercury's northern and southern cusps due to the offset of its dipole magnetic field? (3) can ION sputtering explain all or only part of the NA loss from the planet? And (4) how are mercury's spectrophotometric properties altered by solar wind ions? For the laboratory portion of this work, we will construct a novel beam line configuration to irradiate regolith-like loose powders from above and perform in-situ 350-2500 NM spectroscopic analyses in vacuo, thereby avoiding atmospheric contamination of the irradiated samples. Samples will be prepared in an inert environment to further minimize surface contamination by atmosphere. We will irradiate the samples with h+ and he+ beams at typical solar wind energies of 1 KEV/AMU, where AMU is atomic mass unit. These elements make up ~95% and ~5% of the solar wind, respectively. We know of no other laboratory in the world with all of the above capabilities. State-of-the-art ION irradiation studies have used flat surfaces (i.e., slabs) or powders which have either been highly compressed or epoxied. None of these are reliable simulants for the loose powders expected to comprise regoliths. Most previous irradiation studies with h+ and he+ have used energies 10-1000 times higher. Other have used ions of c, n, o, NE, and AR at too high energies. These elements comprise