The Van Allen Probes Mission consists of two identical spacecraft flying in highly elliptical orbits, with perigee altitudes originally near 600 km. During the low altitude periods of the orbits, the spacecrafts are immersed in a region of high-density atomic Oxygen. Atomic Oxygen is known to change and degrade the properties of spacecraft surfaces, such as those of the Van Allen Probes Electric Field and Waves (EFW) instrument. The consistency of the sensor surfaces in EFW is important because the mechanisms used to ensure the collection of high quality electric field measurements requires that the photoemission properties of each sensor are uniform and stable. Oxidation or erosion of the sensor surfaces could limit the instrument’s ability to balance the currents produced by both the plasma electrons and the controlled bias current applied to the sensors, and thus to properly operate the device. We have modeled the atomic Oxygen exposure to the spacecraft to help determine the impact it has had on the sensors. We have calculated the fluence (time integrated flux) of atomic Oxygen particles that have collided with the spacecrafts over the entire course of the mission. We have also looked at the distribution of atomic Oxygen flux over time to further analyze malfunctions in the sensor readings at different points along the course of the mission. Additionally, we have investigated how different surfaces of the spacecraft are affected differently due to their orientation with respect to the spacecraft’s motion.

During the Twin Rockets to Investigate Cusp Electrodynamics (TRICE-2) High-Flyer rocket’s passage through the cusp the high frequency (HF) radio wave receiver observed three intervals of banded Upper-Hybrid (UH) waves. The bands begin at the UH frequency ($\sim$1.2–1.3 MHz), descending to as low as 1.1 MHz, with amplitudes of hundreds of mV/m. The spacing of the bands are $\sim$4.5–6 kHz and the number of bands ranges from three to ten. Simultaneously, the very low frequency (VLF) radio wave receiver observed Lower-Hybrid (LH) waves with amplitudes ranging from 1–10 mV/m and frequencies of 4.5-6 kHz. Slight variations of the spacings of the bands in the UH waves were closely correlated with variations in the LH peak frequencies. Two possible wave-wave interactions are explored to explain this phenomenon: decay of an UH wave into a lower frequency UH wave and a LH wave, and coalescence of independent UH waves and LH waves that spawn UH waves. Using a dispersion relation calculator with electron and ion distribution functions based off those observed by the particle instruments suggests that UH waves, and to a lesser degree LH waves, can be excited by linear instabilities. Kinematic analysis of the waves dispersion relations and the wave matching conditions show that wave-wave interactions linking UH and LH modes are possible through either decay or coalescence. This analysis along with comparisons of the energy densities of the waves, and the ratio of their occupation numbers suggest that the decay process is more likely than coalescence.

The solar wind is slowed, deflected, and heated as it encounters Venus's induced magnetosphere. The importance of kinetic plasma processes to these interactions has not been examined in detail, due to a lack of constraining observations. In this study, kinetic-scale electric field structures are identified in the Venusian magnetosheath, including plasma double layers. The double layers may be driven by currents or mixing of inhomogeneous plasmas near the edge of the magnetosheath. Estimated double layer spatial scales are consistent with those reported at Earth. Estimated potential drops are similar to electron temperature gradients across the bow shock. Many double layers are found in few high cadence data captures, suggesting that their amplitudes are high relative to other magnetosheath plasma waves. These are the first direct observations of plasma double layers beyond near-Earth space, supporting the idea that kinetic plasma processes are active in many space plasma environments.

Above lunar crustal magnetic anomalies, large fractions of solar wind electrons and ions can be reflected and stream back towards the solar wind flow, leading to a number of interesting effects such as electrostatic instabilities and waves. These electrostatic structures can also interact with the background plasma, resulting in electron heating and scattering. We study the electrostatic waves and electron heating observed over the lunar magnetic anomalies by analyzing data from the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon’s Interaction with the Sun (ARTEMIS) spacecraft. Based on the analysis of two lunar flyby events in 2011 and 2013, we find that the electron two-stream instability (ETSI) and electron cyclotron drift instability (ECDI) may play an important role in driving the electrostatic waves. We also find that ECDI, along with the modified two-stream instability (MTSI), may provide the mechanisms responsible for substantial isotropic electron heating over the lunar magnetic anomalies.

In planetary bow shocks, binary particle collisions cannot mediate the conversion of upstream bulk flow energy into downstream thermal energy, and wave-particle interactions in part assume this role. Understanding the contribution of waves to shock heating requires knowledge of the modes that propagate in different classes of shocks; we describe the growth patterns of whistler waves within the Venusian bow shock. Waves with frequencies $f \lesssim 0.1 f_{ce}$, where $f_{ce}$ is the electron cyclotron frequency, preferentially grow at local minima in the background magnetic field $|B_0|$. Quasi-parallel propagating whistlers with frequencies between $0.1 f_{ce}$ and $0.3 f_{ce}$ are strongest at the downstream ramps of these $|B_0|$ minima. Immediately downstream of the shock, whistlers with frequencies $f < 0.1 f_{ce}$ propagate more than 80$^\circ{}$ oblique from $\vec{B}_0$ and have elliptically polarized $\vec{B}$ fields. A prediction from kinetic theory of the orientation of these waves’ $\vec{B}$ ellipses is confirmed to high accuracy.

The spatial scales of whistler-mode waves, determined by their generation process, propagation, and damping, are important for assessing the scaling and efficiency of wave-particle interactions affecting the dynamics of the radiation belts. We use multi-point wave measurements by two Van Allen Probes in 2013-2019 covering all MLTs at L=2-6 to investigate the spatial extent of active regions of chorus and hiss waves, their wave amplitude distribution in the source/generation region, and the scales of chorus wave packets, employing a time-domain correlation technique to the spacecraft approaches closer than 1000 km, which happened every 70 days in 2012-2018 and every 35 days in 2018-2019. The correlation of chorus wave power dynamics using is found to remain significant up to inter-spacecraft separations of 400 km to 750 km transverse to the background magnetic field direction, consistent with previous estimates of the chorus wave packet extent. Our results further suggest that the chorus source region can be slightly asymmetrical, more elongated in either the azimuthal or radial direction, which could also explain the aforementioned two different scales. An analysis of average chorus and hiss wave amplitudes at separate locations similarly shows the reveals different radial and azimuthal extents of the corresponding wave active regions, complementing previous results based on THEMIS spacecraft statistics mainly at larger L>6. Both the chorus source region scale and the chorus active region size appear smaller inside the outer radiation belt (at L< 6) than at higher L-shells.