Proton plasma asymmetries between the hemispheres of Venus’ dayside magnetosheath lying downstream of the quasi-perpendicular ($q_\perp$) and quasi-parallel ($q_\parallel$) sides of the bow shock are characterized using measurements taken by a mass-energy spectrometer. This characterization enables comparison to analogous Earth studies, thereby providing insight as to which plasma phenomena, such as turbulent particle heating, contribute in creating the observed plasma asymmetries in planetary magnetosheaths. A database of dayside bow-shock crossings along with magnetosheath proton densities, bulk speeds, temperatures, and magnetic-field strengths is manually constructed by selecting measurements taken during stable solar-wind conditions. Ratios of these magnetosheath proton parameters are calculated as functions of distance from the central meridian and the upstream Alfvén Mach number to quantify the $q_{\perp/\parallel}$ asymmetries. The density and bulk-speed exhibit $q_\parallel$-favored asymmetries, mirroring those observed at Earth, whereas the magnetic-field strength reveals no significant asymmetry despite expectations based on simulations. The temperatures perpendicular ($T_\perp$) and parallel ($T_\parallel$) to the background magnetic field have $q_\perp$-favored asymmetries while the temperature anisotropy $T_\perp / T_\parallel$ exhibits a $q_\parallel$-favored asymmetry. This trend is opposite to that seen at Earth, suggesting that the different spatial scales of the two planets’ magnetosheaths may affect the impact of turbulent processes on global plasma properties.

The present atmosphere of Venus contains almost no water, but recent measurements indicate that in its early history Venus had an Earth-like ocean. Understanding how the Venusian atmosphere evolved is important not only for Venus itself, but also for understanding the evolution of other planetary atmospheres. In this study, we quantify the escape rates of oxygen ions from the present Venus to infer the past of the Venusian atmosphere. We show that an extrapolation of the current escape rates back in time leads to the total escape of 0.02-0.6 m of a global equivalent layer of water. This implies that the loss of ions to space, inferred from the present state, cannot account for the loss of an historical Earth-like ocean. We find that the O+ escape rate increases with solar wind energy flux, where more energy available leads to a higher escape rate. Oppositely, the escape rate decrease slightly with increased EUV flux, though the small variation of EUV flux over the measured solar cycle may explain the weak dependency. These results indicate that there isn’t enough energy transferred from the solar wind to Venus’ upper atmosphere that can lead to the escape of the atmosphere over the past 3.9 billion years. This means that the Venusian atmosphere didn’t have as much water in its atmosphere as previously assumed or the present-day escape rates don’t represent the historical escape rates at Venus. Otherwise, some other mechanisms have acted to more effectively remove the water from the Venusian atmosphere.

Jovian magnetospheric plasma irradiates the surface of Ganymede and is postulated to be the primary agent that changes the surface brightness of Ganymede, leading to asymmetries between polar and equatorial regions as well as between the trailing and leading hemispheres. As impinging ions sputter surface constituents as neutrals, ion precipitation patterns can be remotely imaged using the Energetic Neutral Atoms (ENA) measurement technique. Here we calculate the expected sputtered ENA flux from the surface of Ganymede to help interpret future observations by ENA instruments, particularly the Jovian Neutral Analyzer (JNA) onboard the JUpiter ICy moon Explorer (JUICE) spacecraft. We use sputtering models developed based on laboratory experiments to calculate sputtered fluxes of H2, O2, and H2O. The input ion population used in this study is the result of test particle simulations using electric and magnetic fields from a hybrid simulation of Ganymede’s environment. This population includes a thermal component (H+ and O+ from 10 eV to 10 keV) and an energetic component (H+, O++, and S+++ from 10 keV to 10 MeV). We find a global ENA sputtering rate from Ganymede of 1.42x10^27 s^-1, with contributions from H2, O2 and H2O of 34%, 17%, and 49% respectively. We also calculate the energy distribution of sputtered ENAs, give an estimate of a typical JNA count rate at Ganymede, and investigate latitudinal variations of sputtered fluxes along a simulated orbit track of the JUICE spacecraft. Our results demonstrate the capability of the JNA sensor to remotely map ion precipitation at Ganymede.

The concept of an Interstellar Probe (ISP) offers an intriguing combination of scientific break-throughs in several disciplines. These include a global view of our heliosphere, unperturbed sampling of the interstellar medium, discoveries of Kuiper Belt Objects, and many others. The current mission concept of the ISP aims at reaching a distance of 1000 au away from the Sun within this century, far beyond the heliopause at roughly 100-200 au. In this presentation, we investigate basic requirements for an Energetic Neutral Atom (ENA) instrument onboard the ISP for the energy range between 10 eV and 5 keV. An ENA is produced when a fast ion exchanges its charge with an ambient neutral atom. The resulting ENA leaves the source region on a straight trajectory, no longer influenced by electromagnetic fields. This allows an ENA camera to image the ion distribution of remote plasma regions. We calculate the energy spectrum of heliospheric ENAs an observer would see from a given vantage point inside or outside the heliopause. Since the global shape of the heliosphere is unknown yet, we use two analytical models to derive proton flowlines for two different heliospheric shapes: the Parker model [Parker 1961] modified with a termination shock and the analytical representation of a full MHD model [Röken et al. 2015, Kleimann et al. 2017]. The ENA intensity then is the line-of-sight integral of proton density times the local density of neutral hydrogen times the charge-exchange cross-section. We disregard any other neutral species inside the heliosphere and we only consider protons as source for ENAs. The proton populations included are the supersonic solar wind and pickup ions inside the termination shock and the shocked solar wind and pickup ions between termination shock and heliopause. The calculated ENA intensities are first compared to the globally distributed ENA flux measured by the Interstellar Boundary Explorer and Cassini in the inner solar system in the energy range from 10 eV to 55 keV. We then proceed to calculate the ENA intensity as seen by an observer at other positions near or beyond the heliopause. These predictions can serve as a rough guideline for the mission concept of ISP: which trajectory offers the most interesting view on the heliosphere in ENAs and which technical requirements should a low-energy ENA imager meet?

We investigate sunward planetary ions in the Martian magnetotail that potentially reduce the amount of escaping ions. The global properties of sunward flows in the Martian magnetotail are characterized, based on over 13-years of ion data (May 2007–December 2020) collected by the ASPERA-3 instrument on Mars Express. We find that sunward flows mainly occur in the vicinity of the crustal fields, implying that crustal fields may play a key role in producing such flows. The occurrence rate and sunward flux are higher during solar maximum rather than solar minimum. However, we identify a relatively low occurrence rate of sunward flows and low sunward flux, suggesting that sunward flows have negligible influence on total ion escape at Mars. This is different from those at Venus, where sunward flows can significantly decrease the total escape rates of ions.

Using over 6 years of magnetic field data (2014.10-2020.12) collected by the Mars Atmosphere and Volatile EvolutioN (MAVEN), we conduct a statistical study on the three-dimensional average magnetic field structure around Mars. We find that this magnetic field structure conforms to the pattern typical of an induced magnetosphere, that is, the interplanetary magnetic field (IMF) which is carried by the solar wind and which drapes, piles up, slips around the planet, and eventually forms a tail in the wake. The draped field lines from both hemispheres along the direction of the solar wind electric field (E) are directed towards the nightside magnetic equatorial plane, which looks like they are “sinking” toward the wake. These “sinking” field lines from the +E-hemisphere (E pointing away from the plane) are more flared and dominant in the tail, while the field lines from the –E-hemisphere (E pointing towards) are more stretched and “pinched” towards the plasma sheet. Such highly “pinched” field lines even form a loop over the pole of the –E-hemisphere. The tail current sheet also shows an E-asymmetry: the sheet is thicker with a stronger tailward J×B force at +E-flank, but much thinner and with a weaker J×B (even turns sunward) at –E-flank. Additionally, we find that IMF Bx can induce a kink-like field structure at the boundary layer; the field strength is globally enhanced and the field lines flare less during high dynamic pressure; however, the rotation of the planet, against expectations, modulate the configuration of the tail current sheet insignificantly.