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We study roles of the thermosphere and exosphere on the Martian ionospheric structure and ion escape rates in the process of the solar wind‐Mars interaction. We employ a four‐species multifluid magnetohydrodynamic model to simulate the Martian ionosphere and magnetosphere. The coldthermosphere background is taken from the Mars Global Ionosphere Thermosphere Model, and the hot oxygen exosphere is adopted from the Mars exosphere Monte Carlo model—Adaptive Mesh Particle Simulator. A total of four cases with the combination of 1‐D (globally averaged) and 3‐D thermospheres and exospheres are studied. The ion escape rates calculated by adopting 1‐D and 3‐D atmospheres are similar; however, the latter are required to adequately reproduce the ionospheric observations by the Mars Atmosphere and Volatile EvolutioN mission. In addition, our simulations show that the 3‐D hot oxygen corona plays an important role in preventing planetary molecular ions (O 2+and CO 2+) escaping from Mars, mainly resulting from the mass loading of the high‐altitude exospheric O+ions. The coldthermospheric oxygen atom, however, is demonstrated to be the primary neutral source for O+ion escape during the relatively weak solar cycle 24. Despite the similar ion loss rate calculated from 1‐D and 3‐D atmospheres, the latter are required to adequately reproduce MAVEN observationsThe hot oxygen corona plays an important role in protecting the Martian ionosphere/thermosphere from the solar wind erosionThe thermospheric oxygen atom is the primary neutral source for O+ion escape during the relatively weak solar cycle 24

We examine for the first time the flare‐induced effects on the Martian hot O corona. The rapid ionospheric response to the increase in the soft X‐ray flux (~800%) facilitates more hot O production at altitudes below the main ionospheric peak, but almost all of these atoms are thermalized before escape. In response to the increase in the extreme ultraviolet (EUV) flux (~170%), the overall upper ionospheric and thermospheric densities are enhanced, and the peak thermospheric responses are found ~1.5 hr later. The photochemical escape rate is predicted to increase by ~20% with the increases in the soft X‐ray and EUV fluxes but decrease rapidly by ~13% about 2.5 hr later before recovering the preflare level. Since escaping hot O atoms are mostly produced at high altitudes where ionization by the EUV flux is the greatest, the main contributor to the 20% increase in escape rate is the enhancement in the EUV flux. We present for the first time the flare‐induced effects on the loss of neutral O atoms from the atmosphere of Mars. This study found that the main contributor to the sudden increase in the O loss rate is the increase in the solar extreme ultraviolet flux during the flare event, which induces more energetic O atoms at high altitudes where they can easily escape to space. Our investigation will contribute to the earlier works on the atmospheric loss from Mars by providing additional knowledge about the variability of the neutral escape. We examine for the first time the flare‐induced effects on the Martian hot O corona and photochemical escapeThe photochemical escape rate increases by ~20% in the case that describes the peak response time of the ionosphere during the flare eventWe found that the main contributor to the increase in escape rate is the enhancement in the EUV flux

The neutral and plasma environment is critical in understanding the interaction of the solar wind and comet 67P/Churyumov‐Gerasimenko (CG), the target of the European Space Agency's Rosetta mission. To serve this need and support the Rosetta mission, we have developed a 3‐D four‐fluid model, which is based on BATS‐R‐US (Block‐Adaptive Tree Solarwind Roe‐type Upwind Scheme) within SWMF (Space Weather Modeling Framework) that solves the governing multifluid MHD equations and the Euler equations for the neutral gas fluid. These equations describe the behavior and interactions of the cometary heavy ions, the solar wind protons, the electrons, and the neutrals. This model incorporates different mass loading processes, including photoionization and electron impact ionization, charge exchange, dissociative ion‐electron recombination, and collisional interactions between different fluids. We simulated the plasma and neutral gas environment near perihelion in three different cases: an idealized comet with a spherical body and uniform neutral gas outflow, an idealized comet with a spherical body and illumination‐driven neutral gas outflow, and comet CG with a realistic shape model and illumination‐driven neutral gas outflow. We compared the results of the three cases and showed that the simulations with illumination‐driven neutral gas outflow have magnetic reconnection, a magnetic pileup region and nucleus directed plasma flow inside the nightside reconnection region, which have not been reported in the literature. A 3‐D coupled neutral gas and multifluid plasma model for a comet is developedFormation of nightside magnetic pileup region is foundNucleus directed plasma flow inside the nightside reconnection region is found

We have compared our 3‐D hot O corona model predictions with the OI 130.4 nm emission detected by Imaging Ultraviolet Spectrograph/Mars Atmosphere and Volatile EvolutioN (IUVS/MAVEN) based completely on our best pre‐MAVEN understanding of the 3‐D structure of the thermosphere and ionosphere. The model was simulated appropriately for the observational conditions. In addition to dissociative recombination (DR) of O2+, DR of CO2+is also considered as an important hot O source. The model predictions showed excellent agreement with the transition altitude, the observed altitude variation of density, and the spatial variation of the corona with respect to the Mars‐Sun geometry. While previous models predicted escape rates covering a range of nearly 100, the brightness of the modeled hot O densities is a factor of ~1.5 lower than the observations. We discuss possible changes to the model that could come from further analysis of MAVEN measurements and that might close the gap between the modeled and observed brightness. We compared our 3‐D model predictions of the hot O corona with the coronal scans taken by IUVS/MAVENThe transition altitude and altitude vitiation of hot O show good agreement with the observationsThe 3‐D geographic variability of the model prediction is also seen in the IUVS coronal scans

Due to Venus not having a substantial planetary magnetic field the fast‐flowing solar wind plasma can propagate to regions close to the planet. Therefore, thermal atomic oxygen in the thermosphere, hot oxygen in the corona, and the resulting pickup oxygen ions are essential for determining the overall interaction of the planet with plasma of the ambient solar wind. To investigate this complex system, we have initiated a project where a combination of Venus Thermosphere General Circulation Model (VTGCM) and Adaptive Mesh Particle Simulator (AMPS) codes are used to determine the variability of the ”hot” O corona depending on the solar conditions. Here we present the results of modeling Venus' oxygen corona using the VTGCM ionosphere/thermosphere and AMPS kinetic particle models. VTGCM produces a self‐consistent calculation of the thermosphere/ionosphere, providing the spatial distributions of the dominant species. That is further used in AMPS’ modeling of Venus' exosphere (a) to specify the source of the newly created hot O atoms produced by dissociative recombination of O2+${\mathrm{O}}_{2}^{+}$ions and (b) to account for thermalization of these energetic oxygen atoms as they propagate in the upper thermosphere. The altitude distribution of hot O calculated for the solar maximum conditions agree well with Pioneer Venus Orbiter observations of the oxygen corona. The modeling that we have performed for the solar minimum conditions indicates a decrease of the oxygen density in the corona by almost a factor of six compared to that at solar maximum. That is consistent with the non‐detection of the oxygen corona from Venus Express. As expected, the solar moderate case is between the solar maximum and minimum cases. Here we present an investigation of the variability of Venus' extended oxygen corona. For that, we employ a combination of fluid modeling for simulating Venus' ionosphere and thermosphere and kinetic modeling of the source and transport of energetic hot O atoms in the thermosphere. We have found a good agreement of the model results with the Pioneer Venus Orbiter observations of the “hot” O corona. We also found that the oxygen density strongly depends on solar conditions and varies by a factor of six over a solar cycle. That explains why the extended oxygen corona was observed only at the solar maximum. The result presented in this paper will be a part of a later study of the planet's interaction with the ambient solar wind, where the corona model would be used to calculate the mass loading coefficient. The density of Venus' extended oxygen corona varies almost by a factor of six of magnitude during a solar cycleKinetic modeling reproduces PVO observations of Venus' “hot” oxygen corona when forward scattering of the energetic oxygen atoms is employedThe strong dependence of the oxygen density in the corona from solar conditions suggested by results of our modeling is consistent with the non‐detection of the oxygen corona from Venus Express conducted at solar minimum conditions The density of Venus' extended oxygen corona varies almost by a factor of six of magnitude during a solar cycle Kinetic modeling reproduces PVO observations of Venus' “hot” oxygen corona when forward scattering of the energetic oxygen atoms is employed The strong dependence of the oxygen density in the corona from solar conditions suggested by results of our modeling is consistent with the non‐detection of the oxygen corona from Venus Express conducted at solar minimum conditions

The Rosetta spacecraft is en route to comet 67P/Churyumov-Gerasimenko for a rendezvous, landing, and extensive orbital phase beginning in 2014. Model studies of the coma will be required not only for planning of the mission and interpretation of spacecraft data, but also for an expectedly large amount of complementary remote observational data that will be obtained in the meantime. A full-scale simulation of the coma under conditions occurring during the mission can be done only on the basis of a kinetic model. In this work we present a newly developed direct simulation Monte Carlo model of a multispecies coma, where components of the coma are coupled through momentum exchange and photochemical processes, and its application to the case of comet Churyumov-Gerasimenko. It is shown that kinetic effects determine the state of the coma, which limits applicability of a hydrodynamics approach. The study of the coma was performed in the region starting from the surface of the nucleus and extending up to 106 km, which allows incorporation of a realistic model of the gas production from the nucleus from a thermophysical model of a porous ice/dust mixture accounting for the thermal reradiation, the subsurface sublimation and recondensation, and the subsurface mass and energy transport. The results obtained present states of the coma for a series of stages throughout the Rosetta mission and can serve for the planning of the mission as well as for the interpretation of ground-based observations during the 2009 and 2016 apparitions.

Data collected by the Fast Imaging Plasma Spectrometer (FIPS) aboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft showed singly charged Na+‐group ions at energies of between 1 and 13 keV in Mercury's northern planetary cusp. Most of these ions are likely formed by either photoionization or charge exchange of exospheric Na atoms, with initial energies of approximately 1 eV or less. FIPS observations did not establish which acceleration mechanism most reasonably accounts for this energy gain. Using the Adaptive Mesh Particle Simulator (AMPS) model, we undertake kinetic simulations of 1 eV Na+test particles through the electric and magnetic fields output from the Block Adaptive Tree Solar wind Roe‐type Upwind Scheme (BATSRUS) global magnetohydrodynamic (MHD) model of Mercury's magnetosphere, in search of plausible explanations for the source of this energization. We find that Na+with initial energy of 1 eV are readily picked up by the Dungey cycle return flow in the dayside magnetosphere. In some cases, this flow provides the energy for the ions to escape into the magnetosheath, and in other cases it energizes the ions to hundreds of eV before they pass immediately into the cusp. Those that escape can be rapidly picked up into the magnetosheath flow, where they are accelerated by pickup again up to tens of keV. These one‐ and two‐stage pickup processes on Mercury's dayside can account for the energies of many of the Na+ions observed in Mercury's northern magnetospheric cusp by MESSENGER. Data collected in orbit at Mercury showed sodium ions in the northern planetary cusp at high energies. The processes that likely create these ions are only responsible for 0.01%–0.1% of that high energy, and no mechanism previously known to operate at Mercury can account for the difference. We model the Mercury system, and the paths of ions through that system, in search of such a mechanism. We find two mechanisms, both involving energization into proton flows, that explain the data observations. Sodium ions (Na+) with initial energy of 1 eV are energized by Dungey cycle return flow in the dayside dipolar regionNa+are not trapped within the dayside dipolar region of MercuryOne‐ and two‐stage pickup processes can energize Na+up to tens of keV entirely on the dayside Sodium ions (Na+) with initial energy of 1 eV are energized by Dungey cycle return flow in the dayside dipolar region Na+are not trapped within the dayside dipolar region of Mercury One‐ and two‐stage pickup processes can energize Na+up to tens of keV entirely on the dayside

Typical planetary and planetary satellite exospheres are in nonequilibrium conditions, which means that a distribution function that describes these environments is far from Maxwellian. It is even more true when considering transportation of energetic ions in planetary magnetospheres, making it necessary to solve the Boltzmann equation in order to capture kinetic effects when modeling evolution of the distribution function describing such environments. Among various numerical methods, the Monte Carlo approach is one of the most used one for solving kinetic equations. That is because of the relative simplicity of implementing and a high degree of flexibility in including new physical processes specific to a particular simulated environment. Adaptive Mesh Particle Simulator (AMPS) was developed as a general‐purpose code for solving the Boltzmann equation in conditions typical for planetary and planetary satellite exospheres. Later, the code was generalized for modeling dusty gas, dust, and plasma, and for simulating transportation of solar energetic particles and galactic cosmic rays in planetary magnetospheres. Here, we present a brief overview of the design, list the implemented physics models, and outline the modeling capabilities of AMPS. The latter is supported by several examples of prior applications of the code. Kinetic modeling is necessary for understanding various phenomena of planetary and space physicsAMPS is a versatile and well‐tested code with a long track record of application to simulate various planetary and heliophysics phenomenaThe paper demonstrates the modeling capabilities of AMPS by presenting several examples of the code's prior application Kinetic modeling is necessary for understanding various phenomena of planetary and space physics AMPS is a versatile and well‐tested code with a long track record of application to simulate various planetary and heliophysics phenomena The paper demonstrates the modeling capabilities of AMPS by presenting several examples of the code's prior application

We examine here for the first time the effects of both global and regional dust storms on the formation of the Martian hot O corona and associated photochemical loss of O. Our study is conducted by utilizing our integrated model framework, which couples our Martian hot O corona model with a multifluid magnetohydrodynamic model for Mars for the dusty and clear atmospheric condition cases. We present our results with the most up‐to‐date cross sections for the O(3P)‐CO2collisions. The main effect of dust storms on the ionosphere is the upward shift of the ionosphere on the dayside, which results in an increase in production of hot O at all altitudes above the ionospheric peak. However, the dust‐induced inflation of the neutral upper atmosphere results in an enhancement in collisional loss of hot O and thus effectively suppresses the hot O density, reducing the global photochemical loss rate by ~28% for the global dust storm scenario. The relative density structure of the hot O corona does not show any significant changes, while its magnitude decreases at all altitudes. We investigated the effect of dust storms on photochemical escape from Mars using up‐to‐date cross sections for O‐CO2collisionsThe storm‐induced upward shift of the ionosphere causes increased production of hot O and efficient thermalization occurs by the inflated thermosphereThe net result is a global photochemical escape rate that is suppressed by ~28% during the global dust storm scenario

The Rosetta spacecraft is en route to comet 67P/Churyumov-Gerasimenko for a rendezvous, landing, and extensive orbital phase beginning in 2014. With a limited amount of available observational data, planning of the mission as well as the interpretation of measurements obtained by instruments on board the spacecraft requires modeling of the dusty/gas environment of the comet. During the mission, the collision regime in the inner coma will change starting from transitional to fully collisionless. As a result, a physically correct model has to be valid at conditions that are far from equilibrium and account for the kinetic nature of the processes occurring in the coma. A study of the multi-species coma of comet 67P/Churyumov-Gerasimenko is presented in our previous paper, where we describe our kinetic model and discuss the results of its application to cases that correspond to the different stages during the mission. In this work, we focus on numerical modeling of the dust phase in the coma of comet 67P/Churyumov-Gerasimenko and its interaction with the surrounding gas. The basic phenomena that govern the dynamics and energy balance of the dust grains are outlined. The effect of solar radiation pressure and the nucleus gravity in limiting the maximum liftable mass of the grains is discussed. The distribution of the terminal velocity of the dust grains as a function of subsolar angle is derived in the paper. We have found that in the regions with high gradients of the gas density, spike-like features can form in the dust flow. The obtained results represent the state of the coma in the vicinity of the nucleus for a series of stages throughout the Rosetta mission. The implications of the model results for future measurements by the GIADA instrument are discussed.