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A model capable of reproducing a set of solar wind parameters along the virtual spacecraft orbit out of an ecliptic plane has been developed. In the framework of a quasi-stationary axisymmetric self-consistent MHD model the spatial distributions of magnetic field and plasma characteristics at distances from 20 to 1200 Solar radii at almost all solar latitudes could be obtained and analyzed. This model takes into account the Sun's magnetic field evolution during the solar cycle, when the dominant dipole magnetic field is replaced by the quadrupole one. Self-consistent solutions for solar wind characteristics were obtained, depending on the phase of the solar cycle. To verify the model, its results are compared with the observed characteristics of solar wind along the Ulysses trajectory during its flyby around the Sun from 1990 to 2009. It is shown that the results of numerical simulation are generally consistent with the observational data obtained by the Ulysses spacecraft. A comparison of the model and experimental data confirms that the model can adequately describe the solar wind parameters and can be used for heliospheric studies at different phases of the solar activity cycle, as well as in a wide range of latitudinal angles and distances to the Sun. [ABSTRACT FROM AUTHOR]

Photoelectron distribution functions in the near-surface layer over the lunar surface are obtained on the basis of the kinetic approach. The results are shown to depend strongly on the quantum yield of lunar regolith. It is demonstrated that photoelectrons with energies of about both 1 eV and 0.1 eV should be observed in the corresponding measurements. [ABSTRACT FROM AUTHOR]

The spatial scale and intensity of Earth's magnetotail current sheet determine the magnetotail configuration, which is critical to one of the most energetically powerful phenomena in the Earth's magnetosphere, substorms. In the absence of statistical information about plasma currents, theories of the magnetotail current sheets were mostly based on the isotropic stress balance. Such models suggest that thin current sheets cannot be long and should have strong plasma pressure gradients along the magnetotail. Using Magnetospheric Multiscale and THEMIS observations and global simulations, we explore realistic configuration of the magnetotail current sheet. We find that the magnetotail current sheet is thinner than expected from theories that assume isotropic stress balance. Observed plasma pressure gradients in thin current sheets are insufficiently strong (i.e., current sheets are too long) to balance the magnetic field line tension force. Therefore, pressure anisotropy is essential in the configuration of thin current sheets where instability precedes substorm onset. Plain Language Summary: Interaction between solar wind plasma flows and Earth's magnetic field forms the magnetotail, an elongated plasma region in the nightside magnetosphere with strong equatorial sheet‐like plasma currents. That current sheet's spatial scales and intensity determine the magnetotail configuration, which is critical to one of the most energetically powerful phenomena in the Earth's magnetosphere, substorms. In the absence of statistical information about plasma currents, theories based on the isotropic stress balance imply current sheets that are insufficiently intense and thin to trigger substorms. Using MMS and THEMIS observations and global simulations, we explore magnetotail current sheet configuration. We find that the magnetotail current sheet is thinner than expected from theories that rely on isotropic stress balance. Therefore, pressure anisotropy is essential to the prolonged thin current sheet stability that precedes substorm onset, and thus it must be included in space weather models. Key Points: We conduct statistics on current densities in the magnetotail current sheet using Magnetospheric Multiscale and THEMIS observationsThe most intense and thinnest current sheets cannot be described by isotropic pressure balanceComparison of statistical observations with global magnetohydrodynamic and hybrid simulations confirm main findings [ABSTRACT FROM AUTHOR]

Abstract We use Cluster and THEMIS simultaneous observations to study the spatial distributions of a shear B Y field in the Plasma Sheet (PS) of the Earth's magnetotail at −31 R E < X < −9 R E. The best correlation between the B Y field in the PS (B Y _PS) and the Y -component of the Interplanetary Magnetic Field (IMF) (B Y _IMF) was observed during the quiet PS periods when high speed plasma flows were not detected. During active PS periods the correlation between the B Y _PS and B Y _ IMF was poor. The analysis of spatial distribution of the B Y field along the direction perpendicular to the Current Sheet (CS) plane showed the presence of one of the following configurations, which can be self-consistently generated in the CS: 1) the “quadrupole” distribution of the B Y field usually associated with the Hall current system in the vicinity of X-line and 2) the symmetrical “bell-shaped” distribution formed due to the B Y amplification near the neutral plane of the CS. Multipoint observations revealed the transient appearance of the “quadrupole” B Y distribution during the periods of X-line formation in the mid-tail. This distribution was observed during a few minutes within, at least, 12 R E from the estimated X-line position. On the contrary, the symmetrical “bell-shaped” distribution is more localized in the radial direction and, generally, has a larger observation time (up to ∼10 min). Thus, the internal CS perturbations caused either by the Hall currents related to reconnection or by the peculiarities of the local quasi-adiabatic ion dynamics sufficiently affect the shear B Y field existing in the magnetotail due to the partial IMF penetration. Highlights • The best correlation of the PS By field and IMF By is observed during quiet periods. • A By field in the PS is significantly modulated by the internal processes. • Two spatial distributions of By field are self-consistently generated in the PS. • Hall current By-distribution has short duration but is observed at large radial scale. • “Bell-shaped” By-distribution is spatially localized and has long (>10 min) duration. [ABSTRACT FROM AUTHOR]

Thin current sheets having kinetic scales are an important plasma structure, where the magnetic energy dissipation and charged particle acceleration are the most effective. It is believed that such current sheets are self-consistently formed by the specific nonadiabatic dynamics of charged particles and play a critical role in many space plasma and astrophysical objects. Current sheets in the near-Earth plasma environment, e.g., the magnetotail current sheet, are readily available for in-situ investigations. The dedicated multi-spacecraft Cluster mission have revealed basic properties of this current sheet, which are presented in this review: typical spatial profiles of magnetic field and current density, distributions of plasma temperature and density, role of heavy ions and electron currents, etc. Being important for the Earth magnetosphere physics, the new knowledge also could provide the basis for advancement in general plasma physics as well as in plasma astrophysics. [ABSTRACT FROM AUTHOR]

Knowledge of the ion composition in the near-Earth's magnetosphere and plasma sheet is essential for the understanding of magnetospheric processes and instabilities. The presence of heavy ions of ionospheric origin in the magnetosphere, in particular oxygen (O), influences the plasma sheet bulk properties, current sheet (CS) thickness and its structure. It affects reconnection rates and the formation of Kelvin-Helmholtz instabilities. This has profound consequences for the global magnetospheric dynamics, including geomagnetic storms and substorm-like events. The formation and demise of the ring current and the radiation belts are also dependent on the presence of heavy ions. In this review we cover recent advances in observations and models of the circulation of heavy ions in the magnetosphere, considering sources, transport, acceleration, bulk properties, and the influence on the magnetospheric dynamics. We identify important open questions and promising avenues for future research. [ABSTRACT FROM AUTHOR]

Our investigation is motivated by the recent discovery of asteroids orbiting the Sun and simultaneously staying near one of the Solar System planets for a long time. This regime of motion is usually called the quasi-satellite regime, since even at the times of the closest approaches the distance between the asteroid and the planet is significantly larger than the region of space (the Hill's sphere) in which the planet can hold its satellites. We explore the properties of the quasi-satellite regimes in the context of the spatial restricted circular three-body problem 'Sun-planet-asteroid'. Via double numerical averaging, we construct evolutionary equations which describe the long-term behaviour of the orbital elements of an asteroid. Special attention is paid to possible transitions between the motion in a quasi-satellite orbit and the one in another type of orbits available in the 1:1 resonance. A rough classification of the corresponding evolutionary paths is given for an asteroid's motion with a sufficiently small eccentricity and inclination. [ABSTRACT FROM AUTHOR]

Abstract: An expression for the quasi-random jump of the adiabatic invariant at a separatrix crossing is obtained for a slow–fast Hamiltonian system with two degrees of freedom in the case when the separatrix passes through a degenerate saddle point in the phase plane of the fast variables. The general case with an arbitrary degree of degeneracy was considered, and this degree is assumed to remain fixed in the process of evolution of the slow variables. The typical value of the jump is larger than in the non-degenerate case studied earlier. Though strongly degenerate, such a setting can be relevant for physical problems. The influence of the asymmetry of a phase portrait on the magnitude of adiabatic invariant jumps was considered as well. An example of this kind is studied, namely the motion of ions in current sheets with complex inner structure. [Copyright &y& Elsevier]

Abstract: We have used a global time-dependent magnetohydrodynamic (MHD) simulation of the magnetosphere and particle tracing calculations to determine the access of solar wind ions to the magnetosphere and the access of ionospheric O+ ions to the storm-time near-Earth plasma sheet and ring current during the September 24–25, 1998 magnetic storm. We found that both sources have access to the plasma sheet and ring current throughout the initial phase of the storm. Notably, the dawnside magnetosphere is magnetically open to the solar wind, allowing solar wind H+ ions direct access to the near-Earth plasma sheet and ring current. The supply of O+ ions from the dayside cusp to the plasma sheet varies because of changes in the solar wind dynamic pressure and in the interplanetary magnetic field (IMF). Most significantly, ionospheric O+ from the dayside cusp loses access to the plasma sheet and ring current soon after the southward turning of the IMF, but recovers after the reconfiguration of the magnetosphere following the passage of the magnetic cloud. On average, during the first 3h after the sudden storm commencement (SSC), the number density of solar wind H+ ions is a factor of 2–5 larger than the number density of ionospheric O+ ions in the plasma sheet and ring current. However, by 04:00UT, ∼4h after the SSC, O+ becomes the dominant species in the ring current and carries more energy density than H+ ions in both the plasma sheet and ring current. [Copyright &y& Elsevier]

Abstract: We have investigated the population of the magnetosphere by ionospheric O+ ions from the dayside during the first 8h of the September 24–25, 1998 magnetic storm by tracing ion trajectories from the ionosphere in time-dependent electric and magnetic fields obtained from a three-dimensional global magnetohydrodynamic (MHD) simulation of the magnetosphere during this storm event. The MHD simulation used WIND data upstream of Earth as input for this storm that began at 2345UT on September 24, 1998, when a magnetic cloud impacted Earth’s magnetosphere. Ions were launched from both hemispheres on the dayside, in a region extending from 11 to 13 MLT and from 70° to 85° invariant latitude at five minute intervals, beginning 2h before storm onset and extending to 8h after the storm commenced. Ions were launched with energies that reflected the effects of ion energization along field lines during this event (e.g. [Cladis, J.B., Collin, H.L., Lennartsson, O.W., Moore, T.E., Peterson, W.K., Russell, C.T., 2000. Observations of centrifugal acceleration during compression of magnetosphere. Geophys. Res. Lett. 27, 915.]), as these effects were not a priori included in the MHD simulation of the event. The ion launch rate was dynamically normalized to observations by using the [Pollock Jr., C.J., Chappell, C.R., Gurnett, D.A., 1990. A survey of upwelling ion event characteristics. J. Geophys. Res. 95, 18–969.] and [Moore, T.E., Peterson, W.K., Russell, C.T., Chandler, M.O., Collier, M.R., Collin, H.L., Craven, P.D., Fitzenreiner, R., Giles, B.L., Pollock, C.J., 1999. Ionospheric mass ejection in response to a CME. Geophys. Res. Lett. 26, 2339.] relationship between the standard deviation of solar wind dynamic pressure and dayside O+ outflow. We found that ionospheric O+ ions had access to the plasma sheet beyond a radial distance of 10 R E before the storm, but gained access to the near-Earth region and partial ring current soon after the sudden commencement. In addition, significant changes to the magnetospheric configuration caused by the variations in solar wind dynamic pressure, most notably the two pressure peaks at 2345 and ∼0145UT resulted in a relative absence of O+ ions from the magnetotail extending from ∼0140 to ∼0300UT. After 0300UT, and for the next hour, the O+ density in the plasma sheet increased to >1cm−3, and O+ was more abundant in the magnetotail compared even to the period immediately following the storm commencement. [Copyright &y& Elsevier]

• Manifestation of magnetic fields at the Moon is lower-hybrid (LH) wave turbulence. • LH turbulence exists in regions of magnetotail interaction with lunar dusty plasmas. • LH waves should be treated in terms of strong turbulence. • Momentum and energy of LH waves are transferred to dust particles. The results are presented of the first investigation of linear and nonlinear processes associated with waves which are related to the presence of magnetic fields in dusty plasmas at the Moon. Excitation of lower-hybrid turbulence in dusty plasmas near the lunar surface is studied. It is shown that the lower-hybrid turbulence can be generated wherever the Earth's magnetotail interacts with the near-surface dusty plasmas at the Moon. The electric fields appearing as a consequence of the presence of lower-hybrid turbulence are estimated. They can make a significant contribution to the total electric field above the lunar surface which should be taken into account in the future experimental investigation of electric fields at the Moon. [ABSTRACT FROM AUTHOR]

We introduce the collection of papers from the first workshop on the habitability of the venusian cloud layer organized by the Roscosmos/IKI-NASA Joint Science Definition Team (JSDT) for Russia's Venera-D mission and hosted by the Space Research Institute in Moscow, Russia, during October 2-5, 2019. The collection also includes three papers that were developed independently of the workshop but are relevant to venusian cloud habitability.

The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today 1 . A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations 2-5 . These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere 6,7 , which-given methane's lifetime of several centuries-predicts an even, well mixed distribution of methane 1,6,8 . Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections 2,4 . We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater 4 would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally.