2025 Articles

Revisiting Electronic and Nuclear Sputtering from Ions at Mercury using Linear Cascade Theory

Tucker, Orenthal J.; Morrissey, Liam S.; Killen, Rosemary M.; Burger, Matthew H.; Vervack, Jr., Ronald J.; Savin, Daniel Wolf

This study revisits calculations using linear cascade theory (LCT) to estimate the relative importance of the ion-induced collisional sputtering yield (also referred to as knock-on, nuclear, or kinetic sputtering) and the ion-induced electronic sputtering yield. We focus on sputtering of Na from Mercury’s surface using data from the Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) mission. The updated nuclear and electronic sputtering yields for H and He solar wind ions at 1 keV amu⁻ ¹, respectively, are approximately an order of magnitude larger than the values calculated using LCT in M. A. McGrath et al. Compared to this earlier work, our study uses a factor of 10 larger Na surface fraction and a factor of 3 lower total atom surface density based on MESSENGER data that were not available when the McGrath et al. study was carried out. Additional differences are the use of new data more relevant to Mercury’s surface minerals for the nuclear and electronic stopping-power cross sections and the surface binding energies. For the conditions considered in this study, the nuclear sputtering yields calculated using LCT show good agreement with the values calculated using recent binary collision approximation models. We qualitatively compare estimates of the Na sputtering source rate to other source processes for Mercury’s exosphere, considering recent studies of the precipitating ion flux based on MESSENGER data. Future experiments that measure the yield and ejecta energy spectra for simulated Mercury surface conditions, along with advanced modeling of ion–surface interactions, are required to reduce uncertainties and support exospheric studies.