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Screenshot of slide. Title: The Possibility of Dielectric Breakdown Weathering Throughout the Solar System. Content: Laboratory and spacecraft experiments show that electrical insulators exposed to sufficiently high fluxes of energetic charged particles experience dielectric breakdown, or
Screenshot of slide. Title: Exosphere Formation, Solar-Wind-Ion Sputtering, and the Importance of Surface Binding Energy (SBE). Text: For 40 years, researchers studying how exospheres form on airless bodies have been hindered by a poor understanding of solar wind ion sputtering. These ion impacts on airless bodies play an important role in altering surface properties and the surrounding environment. Sputtering data relies on user-defined Surface Binding Energies (SBEs), which determine the sputtering yield and energy distribution, but these SBEs are not reliably known for many materials such as plagioclase feldspars and sodium pyroxenes, which are expected to be important for exospheric formation at Mercury and the Moon. SSERVI LEADER team (Morrissey et al. 2022) have developed a novel method of using molecular dynamics (MD) simulations to simulate mineral surfaces on the atomistic scale and directly quantify silicate SBEs. Results show that increasing SBEs from 1.1 eV to 7.9 eV increases the % sputtered Na atoms above escape energy from 55% to 95%. This has a significant effect on the predicted solar wind ion sputtering yield and energy distribution of Na and the formation of the corresponding Na exosphere. This is important to Planetary Science as these new MD SBE results will enable more accurate predictions for solar wind ion sputtering contributions to the exosphere of Mercury and the Moon. [Graph 1 of 2 shows: Na sputtering energy yield vs Na surface binding energy (negatively correlated, asymptotically approaching 0). Graph 2 of 2 shows: % of sputtered Na atoms escaped vs. Na surface binding energy (positively correlated, asymptotically approaching 100%).] Results show Na SBE derived for albite is 30x higher than values previously used in sputter calculations, decreasing the yield by a factor of over 30! SBEs for minerals can be 8x higher than the monoelemental cohesive energy approximation often used to estimate compound SBEs. Citation: Morrissey, L. S., Tucker, O. J., Killen, R. M., Nakhla, S., & Savin, D. W. (2022). 'Solar Wind Ion Sputtering of Sodium from Silicates Using Molecular Dynamics Calculations of Surface Binding Energies.' The Astrophysical Journal Letters, 925(1), L6
Screenshot of slide. Title: Martian Ions Sputter the Surface of Phobos. Content: Mars' closest moon, Phobos, is bombarded by positively charged ions coming not only from the solar wind, but also directly from the Martian atmosphere. These ions sandblast the moon's surface and kick some of that material back out into space in a process called sputtering. Using observations of ions obtained by the NASA Mars Atmosphere and Volatile Evolution mission (MAVEN), in orbit around Mars since 2014, scientists have confirmed that ions coming from Mars dominate solar wind ions in sputtering the surface of Phobos in the nightside. Researchers also found that the flux of material liberated from the moon's surface can increase by a factor of 50 during solar wind events. This is the first time that the unique link between planetary atmospheric escape at Mars and the surface processing of its moon has been confirmed with in-situ ion measurements. [Graphic: Illustration of solar wind bombarding Phobos.] Phobos is bombarded by protons and alpha particles from the solar wind and by Martian atomic and molecular oxygen ions. 4 years of ion observations from MAVEN at the orbit of Phobos show that Martian ions O+ and O2 + significantly sputter the surface of the moon. [Graph showing rough anti-correlation between flux of material ejected from the surface of Phobos by impacting ions coming from two sources: the solar wind, and the martian ionosphere and exosphere.] Citation: Nénon, et al. (2019).
Screenshot of slide: Title: Simulating Artificial Lunar Atmospheres. Content: Almost any lunar landing will involve the release of spacecraft exhaust gases into the lunar environment, creating a thin, temporary lunar atmosphere. Computer simulations can predict how these gases behave. Comparing simulation results to observations of the lunar exosphere during future lunar landings can address important questions, such as-- how do spacecraft systems alter their environments? Specific science questions are-- How far should a rover travel to reach an area uncontaminated by exhaust gases? How fast does water (a common exhaust gas) migrate to permanently shadowed regions near the lunar poles? Monitoring the lunar atmosphere during and after lunar landings can help in planning missions and can address outstanding science questions. [Graphs showing two possible H2O gas density scenarios at 155 s after thruster firing commences. Possible outcomes depend on how strongly water adsorbs to the surface.] Citation: P. Prem, D.M. Hurley, D.B. Goldstein, P.L. Varghese (2020), The Evolution of a Spacecraft-Generated Lunar Exosphere. JGR Planets (https://doi.org/10.1029/2020JE006464). The PI of the LEADER SSERVI project is Rosemary Killen (695) of NASA Goddard Space Flight Center. To enable screen reader support, press Ctrl+Alt+Z To learn about keyboard shortcuts, press Ctrl+slash
Screenshot of slide. Title: Cosmic Rays and the Weakening Solar Cycle. Content: The sunspot cycle has been trending weaker since the 1950s. The GCR (galactic cosmic radiation) doses will probably exceed the already high values. The radiation environment will limit long-term missions. [Graph comparing past and present Dalton and Gleissberg cycles of solar activity.] The [current] persistent decline in solar activity resembles past secular minima. 'Galactic Cosmic Radiation in Interplanetary Space Through a Modern Secular Minimum', published in Space Weather, investigates the radiation levels and permissible mission durations in deep space. In the 1990s, astronauts could travel through space for as much as 1000 days before they hit NASA safety limits on radiation exposure. In the coming years, cosmic rays could limit trips to as little as 290 days for 45-year old male astronauts, and 204 days for females. [Graphic showing that cosmic radiation will limit space travel duration as stated.] For long-term missions, solar maximum is safer since galactic cosmic radiation falls to lower levels. Lunar missions are less limiting as transiting to the Moon and back takes a shorter time than the values found here, and shielding is
Screenshot of slide. Title: Solutions for a challenging electrical environment; lunar permanently shadowed regions. Text is broken down into two sections. PROBLEM: The lunar polar crater environment is dark and plasma-poor, i.e. lacks electrical grounding. [Rhodes & Farrell, Journal of Geophysical Research, 2019]. Triboelectric charging (static electricity) can develop large voltage on equipment; rover, space-suit, drill… [Rhodes & Farrell, Advances in Space Research, submitted]. SOLUTION EFFORTS: Defining low-grounding 'keep-away' zones. Modeling/simulation of grounding methods (portable UV light source, cable to iluminated surface, mirror/lens sunlight diversion). NEXT STEP: Experiments to measure static charge accumulation. Contact: Dov Rhodes and William Farrell, NASA GSFC (william.m.farrell@nasa.gov). Graphic 1/2: Graph showing charge buildup on drill chassis over time (approaching -10^3 volts within 10 seconds). Graphic 2/2: Illustration of rover in deep lunar crater, credited to Jay Friedlander/NASA GSFC.