Outside the Martian bow shock, charge exchange between solar wind protons and exospheric hydrogen produces energetic neutral atoms (ENAs) that travel towards Mars at the solar wind velocity. The penetrating ENAs deposit most of their energy near 150 km, but a fraction of them undergo enough collisions to be scattered back to space, resulting in a hydrogen albedo. Some of the penetrating ENAs are converted into protons upon reaching the collisional upper atmosphere. These protons can be measured by the Mars Atmosphere and Volatile EvolutioN’s Solar Wind Ion Analzyer (SWIA) during periapsis passes, providing information about the penetrating and backscatter populations. In this work, we perform the first detailed analysis of the backscatter and albedo using SWIA observations. We find that our calculated backscatter energy spectra are consistent with model predictions and that, as expected, the penetrating and backscatter particle fluxes increase with solar wind speed and decrease with solar zenith angle (SZA). We also find that the albedo, which has an average value of 0.20±0.16, decreases with solar wind speed and increases at high SZAs near the terminator.

In October 2014, the close encounter between Mars and comet Siding Spring produced a transient ionized layer in the upper atmosphere composed primarily of Mg⁺ ions. The layer was detected by instruments on three spacecraft, including the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on Mars Express. Analyses of the MARSIS data indicated the transient layer persisted up to ~19 hours after the comet’s closest approach. We report MARSIS observations that suggest the transient layer lasted at least 7 days – and potentially as long as 32 days – after closest approach. During this period, the transient layer was mostly confined to a narrow latitude range between 20°N-60°N and a longitude range spanning 275°E to 95°E. Since this period coincided with a highly active Sun, we discuss how solar flares may have contributed to the layer’s prolonged lifetime.

We report observations of reconnection exhausts and associated ion and electron separatrix layers in and around the Heliospheric Current Sheet (HCS) during PSP Encounters 08 and 07, at 16 Rs and 20 Rs. HCS reconnection accelerated protons to almost twice the solar wind speed and increased the proton core energy by a factor of ~3, due to the Alfvén speed being comparable to the solar wind flow speed at these near-Sun distances. During E08, accelerated protons were found to have leaked out of the exhaust along separatrix field lines, appearing as field-aligned energetic proton beams in a broad region outside the HCS. Concurrent dropouts of strahl electrons, indicating disconnection from the Sun, provide further evidence for the HCS being the source of the beams. Around the HCS in E07, there were also proton beams but without electron strahl dropouts, indicating that their origin was non-local and closer to the Sun.

We present here an in-depth analysis of one time interval when quasi-linear mirror mode structures were detected by magnetic field and plasma measurements as observed by the NASA/Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We employ ion and electron spectrometers in tandem to support the magnetic field measurements and confirm that the signatures are indeed mirror modes. Wedged against the magnetic pile-up boundary, the low-frequency signatures lasted on average ~10 s with corresponding sizes of the order of 15-30 upstream solar wind proton thermal gyroradii, or 10-20 proton gyroradii in the immediate wake of the quasi-perpendicular bow shock. Their peak-to-peak amplitudes were of the order of 30-35 nT with respect to the background field, and appeared as a mixture of dips and peaks, suggesting that they may have been at different stages in their evolution. Situated in a marginally stable plasma with β|| ~ 1, we hypothesise that these so-called magnetic bottles, containing a relatively higher energy and denser ion population with respect to the background plasma, were formed upstream of the spacecraft behind the quasi-perpendicular shock. These signatures are very reminiscent of magnetic bottles found at other unmagnetised objects such as Venus and comets, also interpreted as mirror modes. Our case study constitutes the first unambiguous detection of mirror modes around Mars, which had up until now only been surmised because of the lack of high-temporal resolution plasma measurements.

The study of lunar plasma environment’s response to the magnetotail lobe condition is the main subject of our investigation in this report. Photoionization and charge exchange of protons with the lunar exosphere arethe ionization processes included in our model. The computational model includes the dynamics of heavy Na+ pickup and ambient magnetospheric ions. The electrons are considered as a fluid.The lunar interior is considered as a weakly conducting body. In this report we consider for the first time a formation of lunar plasma structures, wakes, and a generation of low-frequency electromagnetic waves by using a self-consistent hybrid kinetic modeling. The input parameters were taken from the ARTEMIS observations. At an early stage the Moon with exosphere and conducting core excites whistler waves in case of Sub-Alfvenic/sonic interaction. At a later stage an excitation of the Alfven wave is observed. The topology of the Alfven waves is approximately similar to the Alfven wing near the planetary moons (Io, Europa etc.). The physics of the Moon-magnetotail lobe interaction is also close to the physics of the interaction between plasma clouds (expanding and not expanding) and ambient magnetospheric plasma. The heavy pickup ions create a large structured halo with space scale of more than 10 R_{E} in the direction of the background field. The modeling also shows an excitation of the compressional waves due to expansion of heavy exospheric pickup ions. The lunar model with weaker interior conductivity excites lower levels of the wave activity. This work was supported by NASA Award (80NSSC20K0146) from Solar System Workings Program (NNH18ZDA001N-C.3-SSW2018). Computational resources were provided by the NASA High-End SupercomputingFacilities (Aitken-Ames, Project HEC SMD-20-02357875).

Quasi-Thermal Noise (QTN) spectroscopy is a reliable diagnostic routinely used for measuring electron density and temperature in space plasmas. The observed spectrum depends on both antenna geometry and plasma kinetic properties. Parker Solar Probe (PSP), launched in 2018, is equipped with an antenna system consisting of two linear dipoles with a significant gap between the antenna arms. Such a configuration, not utilized on previous missions, cannot be completely described by current models of the antenna response function. In this work, we calculate the current distribution and the corresponding response function for the PSP antenna geometry, and use these results to generate synthetic QTN spectra. Applying this model to the Encounter 7 observations from PSP provides accurate estimations of electron density and temperature, which are in very good agreement with particle analyzer measurements.

We utilize measurements from instruments on the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to investigate singly ionized helium formed by charge exchange between solar wind alpha particles and neutral hydrogen in the region upstream from Mars. We show that the observed helium ion signal varies with solar wind speed and spatial location in a manner consistent with expectations for a charge exchange source. We find that the ratio of singly to doubly ionized helium varies with Martian season, with a peak in the southern summer season. The inferred neutral hydrogen column density and the seasonal variation thereof agree with the results of previous studies based on other measurement techniques. The MAVEN helium ion measurements provide a new method of probing the hydrogen corona, with nearly continuous coverage of the Martian seasonal cycle across the entire mission, enabling study of the interannual variability of the Martian exosphere.

Collisionless shocks in space plasma are regions of heating and acceleration of charged particles and dissipation of kinetic energy. These accelerated particles are the source of electromagnetic emissions from supernova remnants and other astrophysical structures. At high Mach numbers, shocks can be inherently nonstationary and exhibit modulated energy transfer and recurring plasma compression areas in the form of reformation. We use data from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft to study reformation of the Martian bow shock which has a relatively high curvature compared to that at Earth and the upstream solar wind is often mass loaded with a population of pickup ions. We show evidence of ion reflection effects in reformation of a supercritical quasi-perpendicular shock.

Magnetic holes (MHs) are pressure-balanced structures characterized by distinct decreases in the interplanetary magnetic field (IMF) strength in otherwise unperturbed solar wind. In this paper we present an analysis of MHs upstream of the Martian bow shock based on three months of observations by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Plasma properties within and around these structures as well as their shape characteristics are examined. We find an occurrence rate of around 2.1 events per day. About 48 percent of all events are of linear type with magnetic field rotation across the hole less than 10 degrees. We observe linear magnetic holes both as isolated events and as part of a train of magnetic holes. The proton temperature anisotropy inside MHs increases while alpha particles remain mostly isotropic. The average electron temperature inside MHs modestly increases with increasing hole depth. The duration of linear holes at 1.5 AU shows an increase compared to durations at smaller heliocentric distances, but the structures remain asymmetrical and ellipsoid. A case study of MHs accompanied by a population of heavy pickup ions is also discussed.