arXiv subjects

Gabriella Stenberg Wieser

Publications and source records attributed to Gabriella Stenberg Wieser.

4 recordsLinked to original sources

arXiv2026

Scattering and sputtering on the lunar surface; Insights from negative ions observed at the surface

Context. Airless planetary bodies are directly exposed to solar wind ions, which can scatter or become implanted upon impact with the regolith-covered surface, while also sputtering surface atoms. Aims. We construct a semi-analytical model for the scattering of ions of hundreds of eV and the sputtering of surface atoms, both resulting in the emission of negative ions from the lunar surface. Our model contains a novel description of the scattering process that is physics-based and constrained by observations. Methods. We use data from the Negative Ions at the Lunar Surface (NILS) instrument on the Chang'e-6 lander to update prior knowledge of ion scattering and sputtering from lunar regolith through Bayesian inference. Results. Our model shows good agreement with the NILS data. A precipitating solar wind proton has roughly a 22% chance of scattering from the lunar surface in any charge state, and about an 8% chance of sputtering a surface hydrogen atom. The resulting ratio of scattered to sputtered hydrogen flux is eta_sc / eta_sp = 1.5 for a proton speed of 300 km/s. We find a high probability (7-20%) that a hydrogen atom leaves the surface negatively charged. The angular emission distributions at near-grazing angles for both scattered and sputtered fluxes are controlled by surface roughness. Our model also indicates significant inelastic energy losses for hydrogen interacting with the regolith, suggesting a longer effective path length than previously assumed. Finally, we estimate a surface binding energy of 5.5 eV, consistent with the observations. Conclusions. Our model describes the scattering and sputtering of particles of any charge state from any homogeneous, multi-species surface. Using NILS data, we successfully applied the model to update our understanding of solar wind interacting with lunar regolith, and the emission of negative hydrogen ions.

physics.space-ph↗

arXiv2025

Kinetic-Scale Physics of a Multi-Species Solar Wind

The solar wind affects the plasma environment around all solar system bodies. A strong solar wind dynamic pressure pushes plasma boundaries closer to these objects. For small objects kinetic effects on scales smaller than an ion gyroradius play an important role, and species with various mass-per-charge may act differently. In this case the solar wind composition can be important. Protons are the dominant ion species in the solar wind; however, sometimes the density of alpha particles increases significantly. We analyse the effect of different solar wind alpha-to-proton ratios on the plasma boundaries of the induced cometary magnetosphere. In addition, we investigate the energy transfer between the solar wind ions, the cometary ions, and the electromagnetic fields. Using the hybrid model Amitis, we simulate two different alpha-to-proton ratios and analyse the resulting plasma structures. We calculate the power density (E.J) of all three ion species (solar wind protons and alphas, and cometary ions) to identify load and generator regions. The integrated 1D power density shows the evolution of the power density from the upstream solar wind to downstream of the nucleus. A higher alpha-to-proton ratio leads to a larger comet magnetosphere but weaker magnetic field pile-up. The protons transfer energy to the fields and the cometary ions in the entire upstream region and the pile-up layer. Upstream of the nucleus, alphas are inefficient in transferring energy and can act as a load, especially for low alpha-to-proton ratios. The transfer of energy from alphas to cometary ions happens further downstream due to their larger inertia. For a multi-species solar wind the mass loading and energy transfer upstream of the pile-up layer will be most efficient for the species with the lowest inertia, typically protons, since different ion gyroradii give different flow patterns for the individual species.

physics.space-ph↗

arXiv2024

Cometary ion drift energy and temperature at comet 67P-Churyumov/Gerasimeko

The Ion Composition Analyzer (ICA) on the Rosetta spacecraft observed both the solar wind and the cometary ionosphere around comet 67P/Churyumov-Gerasimenko for nearly two years. However, observations of low energy cometary ions were affected by a highly negative spacecraft potential, and the ICA ion density estimates were often much lower than plasma densities found by other instruments. Since the low energy cometary ions are often the highest density population in the plasma environment, it is nonetheless desirable to understand their properties. To do so, we select ICA data with densities comparable to those of Rosetta's Langmuir Probe (LAP)/Mutual Impedance Probe throughout the mission. We then correct the cometary ion energy distribution of each energy-angle scan for spacecraft potential and fit a drifting Maxwell-Boltzmann distribution, which gives an estimate of the drift energy and temperature for 3521 scans. The resulting drift energy is generally between 11--18 eV and the temperature between 0.5--1 eV. The drift energy shows good agreement with published ion flow speeds from LAP during the same time period and is much higher than the cometary neutral speed. We see additional higher energy cometary ions in the spectra closest to perihelion, which can either be a second Maxwellian or a kappa distribution. The energy and temperature are negatively correlated with heliocentric distance, but the slope of the change is small. It cannot be quantitatively determined whether this trend is primarily due to heliocentric distance or spacecraft distance to the comet, which increased with decreasing heliocentric distance.

astro-ph.EP↗

arXiv2020

Momentum and pressure balance of a comet ionosphere

We calculate the momentum flux and pressure of ions measured by the Ion Composition Analyzer (ICA) on the Rosetta mission at comet 67P/Churyumov-Gerasimenko. The total momentum flux stays roughly constant over the mission, but the contributions of different ion populations change depending on heliocentric distance. The magnetic pressure, calculated from Rosetta magnetometer measurements, roughly corresponds with the cometary ion momentum flux. When the spacecraft enters the solar wind ion cavity, the solar wind fluxes drop drastically, while the cometary momentum flux becomes roughly ten times the solar wind fluxes outside of the ion cavity, indicating that pickup ions behave similarly to the solar wind ions in this region. We use electron density from the Langmuir probe to calculate the electron pressure, which is particularly important close to the comet nucleus where flow changes from antisunward to radially outward.

astro-ph.EP↗