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We report the first global, time-dependent simulation of the Mars upper atmospheric responses to a realistic solar flare event, an X8.2 eruption on 10 September 2017. The Mars Global Ionosphere-Thermosphere Model runs with realistically specified flare irradiance, giving results in reasonably good agreement with the Mars Atmosphere and Volatile EvolutioN spacecraft measurements. It is found that the ionized and neutral regimes of the upper atmosphere are significantly disturbed by the flare but react differently. The ionospheric electron density enhancement is concentrated below ~110-km altitude due to enhanced solar X-rays, closely following the time evolution of the flare. The neutral atmospheric perturbation increases with altitude and is important above ~150-km altitude, in association with atmospheric upwelling driven by solar extreme ultraviolet heating. It takes ~2.5 hr past the flare peak to reach the maximum disturbance and then additional ~10 hr to generally settle down to preflare levels.

A comprehensive modeling study has been conducted to investigate space weather effects at Mars during the 10 September 2017 solar flare, utilizing an integrated framework that combines the global magnetohydrodynamic (MHD) model and Mars Global Ionosphere‐Thermosphere Model (MGITM). This is the first time the thermosphere‐ionosphere‐magnetosphere system is self‐consistently simulated under realistic, time‐varying conditions. Our simulations align well with observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN). Recognizing that complexities due to highly disturbed upstream conditions and rotating crustal fields obscure solar flare effects in orbit‐to‐orbit comparisons, we perform controlled simulations of nonflare and flare cases and exploit their contrast to quantify spatiotemporal variations in flare impact. Our results highlight pronounced and rapid dayside ionospheric perturbations, contrasting with weaker and delayed nightside responses. Notably, in the topside ionosphere, O2+ ${\mathrm{O}}_{2}^{+}$ and CO2+ ${\mathrm{O}}_{2}^{+}$ densities increase primarily on the dayside below ∼ ${\sim} $300 km altitude, peaking with an increase of 20%–30%. The O+ ${\mathrm{O}}^{+}$ density shows a more significant increase of up to ∼ ${\sim} $50%, extending into the magnetosphere and nightside via plasma transport, increasing its total loss rate by 14%. We observe distinct altitude‐dependent patterns in dayside electron density enhancements in percent, characterized by a weakening with altitude and a rapid decay below ∼ ${\sim} $150 km in line with the flare development, and a gradual intensification between ∼ ${\sim} $150–300 km due to plasma transport and flare‐induced atmospheric upwelling. Earlier Mars Global Surveyor observations were limited to the low‐altitude pattern due to atmospheric expansion and missed the higher altitude variations observed by MAVEN. Plain Language Summary: This study investigates the impact of a powerful X8.2‐class solar flare on 10 September 2017 at Mars. Using an integrated modeling framework that combines two state‐of‐the‐art global models, our simulations provide insights into distinct altitude‐dependent patterns of flare‐induced ionospheric density enhancements, pronounced day‐night asymmetry, and a moderate increase in ion escape. Key findings include rapid variations in ionospheric density enhancements at lower altitudes, with a gradual intensification at higher altitudes due to plasma transport and atmospheric upwelling. These findings contribute to a better understanding of how solar flares impact the space environment of unmagnetized or weakly‐magnetized planets like Mars. Key Points: The solar flare causes pronounced and rapid dayside ionospheric perturbations and weaker and delayed effects on the nightsideO2+ and CO2+ densities increase by 20%–30% above 150 km on the dayside, while O+ increases by up to 50% and over larger spacePercentage increase of dayside e− densities decreases with altitude and decays fast below ∼150 km, and rises and decays slowly above that [ABSTRACT FROM AUTHOR]

Understanding the interaction between Mars and the solar wind is crucial for comprehending the atmospheric evolution and climate change on Mars. To gain a comprehensive understanding of the Martian plasma environment, global numerical simulations are essential in addition to spacecraft observations. However, there are still discrepancies among different simulation models. This study investigates how these discrepancies stem from the considered physical processes and numerical implementations. We compare two global multispecies MHD models: the "Sun model" based on the BATS‐R‐US code and the "Sakata model" based on a newly developed multifluid model MAESTRO. By employing the same typical upstream conditions and the same neutral atmosphere for current Mars, along with similar numerical implementations such as inner boundary conditions, we obtain simulation results that exhibit unprecedented agreement between the two models. The dayside results are nearly identical, especially along the subsolar line, indicating the robustness of MHD models to predict dayside interaction under given upstream conditions and ionosphere assumptions. The escape rates of planetary ions are also in good agreement. However, discrepancies remain in the terminator and nightside regions. Detailed numerical implementations, including inner boundary conditions, magnetic field divergence control methods, and radial resolutions, are shown to influence certain aspects of the results greatly, such as magnetotail configuration and ion diffusion. Key Points: The same physical assumptions are employed for two different global multispecies MHD modelsThe results for the dayside interaction and planetary ion escape are in unprecedented good agreementDetails of the numerical implementations influence the results, especially on the nightside [ABSTRACT FROM AUTHOR]

We examine the newly discovered phenomena of sinuous aurora on the nightside of Mars, using images of 130.4 and 135.6 nm oxygen emission measured by the Emirates Mars Mission EMUS ultraviolet spectrograph, and upstream measurements from the MAVEN and Mars Express spacecraft. They are detected in ∼3% of observations, totaling 73 clear detections. These emissions are narrow, elongated (1,000–6,000 km), cross Mars' UV terminator, and are oriented generally toward the anti‐solar point, clustering into north, south, east, and west‐oriented groups. Diverse morphologies are observed, though some spatial features, such as broad curves, may in some cases be due to temporal aliasing of aurora motion as each image is built up over 15–20 min. Sinuous aurora form away from Mars' strongest crustal magnetic fields and can be interrupted by moderate crustal fields. Sinuous aurora occurrence increases strongly with solar wind pressure, though brightness shows only a weak positive dependence on pressure. Interplanetary magnetic field (IMF) clock angle affects their occurrence and orientation: sinuous aurora show a broad range of orientations centered on the solar wind convection electric field (Econv) direction and forming in the +Econv hemisphere, although with moderate clockwise and counterclockwise average "twists" for westward and eastward IMF, respectively. From these features we infer a link between sinuous aurora and electron energization in Mars' magnetotail current sheet, where field geometry on the +Econv side of the sheet is more organized and symmetric. Determination of specific triggering conditions for sinuous aurora requires further investigation. Plain Language Summary: Sinuous aurora are narrow, extended patterns of UV emission caused by long, thin channels of energized electrons striking Mars' nightside upper atmosphere. We study images of these aurora taken by the Emirates Mars Mission EMUS instrument. 73 cases of sinuous auroras were found (∼3% occurrence rate) with lengths ranging from 1,000 to 6,000 km. These auroras usually cross Mars' day‐night boundary and extend in the direction opposite to the Sun. They tend to cluster into groups oriented toward the north, south, east, and west directions with a diverse array of shapes. Sinuous aurora generally form away from Mars' strongest crustal magnetic fields. They occur more frequently for higher solar wind pressure. Their orientations are affected by the interplanetary magnetic field (IMF), displaying a broad range of orientations centered on the direction of the electric field in the solar wind, and forming in the hemisphere to which this electric field points, although with moderate counterclockwise and clockwise average "twists" for eastward and westward IMF, respectively. From these features we infer a link between sinuous aurora and a sheet of current in Mars magnetic tail, wherein the aurora‐causing electrons may be energized before falling into the upper atmosphere to produce aurora. Key Points: These narrow emission features form away from strong crustal fields, oriented anti‐sunward, cross the terminator, are detected in 3% observationsOccurrence increases with solar wind pressure, certain interplanetary magnetic field orientations, and in the positive motional electric field hemisphereSinuous aurora may be related to magnetotail asymmetry and electron energization processes occurring in the tail current sheet [ABSTRACT FROM AUTHOR]

On 26–27 December 2022, Mars experienced an extremely low‐density solar wind stream, which was encountered first by Earth because of the radial alignment of the two planets (i.e., Mars opposition). During this event, two important properties of the ionospheric and magnetospheric states changed significantly in response to the low solar wind ram pressure, as inferred from the superthermal electron observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission. The interface between the ionosphere and magnetosphere expanded to thousands of kilometers, outside of the nominal bow shock locations, coinciding with the expansion of the cold planetary ions. Meanwhile, the ambipolar electrostatic potential arising from the ionospheric electron pressure gradient increased from the nominal ∼ −0.7 to ∼ −2 V (relative to the lower ionosphere). This enhanced ambipolar potential likely facilitated the observed ionosphere expansion. Key Points: This study characterizes Mars's magnetospheric and ionospheric response to the disappearing solar wind event in December 2022During the event, open and closed field lines extend beyond the nominal bow shock location, just as the planetary cold ionsThe ionospheric ambipolar potential drop is enhanced from the nominal ∼ −0.7 to ∼ −2 V, likely facilitating the ionosphere expansion [ABSTRACT FROM AUTHOR]

Despite Venus having insignificant intrinsic magnetic fields, the magnetic connectivity between the solar wind and the Venus ionosphere, or magnetic topology, is not as simple as expected and is also important for characterizing the Venus space environment. This study provides a technique combining superthermal electron energy and pitch angle distributions to infer up to 6 subtypes of magnetic topology at Venus. This enables us to determine magnetic topology with automated procedures using the Venus Express (VEx) observations from May 2006 to November 2014. We find that the draped topology (both ends of a field line not connected to the collisional ionosphere) is the dominant topology in the near‐Venus space environment, >70%, except at low altitudes close to the ionosphere. The open (a field line connected to both the solar wind and the collisional ionosphere) and closed (a field line connected only to the collisional ionosphere) topologies make up 20%–30% on average of the magnetotail and up to 50% at low altitudes. This study provides the first characterization of the statistical distributions of different magnetic topologies at Venus. Plain Language Summary: Venus has insignificant intrinsic magnetic fields and its magnetic environment consists of the solar magnetic field lines draping around the planet, or the so‐called induced magnetosphere. However, some of the draping magnetic fields could penetrate deeply into the Venus collisional atmosphere, producing complex magnetic connectivities in the near Venus space environment. This study provides a technique to determine the magnetic connectivity with automated procedures by using electron and magnetic field measurements obtained from the Venus Express (VEx) mission from May 2006 to November 2014. The statistical distributions of different magnetic connectivities at Venus are characterized for the first time. The findings of this study further our understanding of the Venus magnetosphere. Key Points: This study provides a technique combining superthermal electron energy and pitch angle distributions to infer magnetic topology at VenusThe statistical distributions of different magnetic topologies at Venus are characterized for the first timeThe closed and open topologies have high occurrence rates at low altitudes while the draped topology dominates other regions [ABSTRACT FROM AUTHOR]

We study the average global distribution of the external magnetic field at Mars, and its variability with the upstream solar wind dynamic pressure and interplanetary magnetic field as well as with the ambient crustal magnetic field strength. Our approach involves excluding the intrinsic planetary field from the total magnetic field by applying a crustal field model previously derived using low altitude measurements. The distribution of the average external field that remains is statistically analyzed using nearly 8 years of Mars Atmosphere and Volatile EvolutioN (MAVEN) observations and several global, time‐dependent magnetohydrodynamic simulations. Overall consistent results have been obtained from the data and model, which are complementary to each other and cross validate the findings. It is found that the external field is significantly enhanced from the upstream across the bow shock (BS) and further intensifies closer to the planet in the topside ionosphere. It peaks at ∼170 km altitude near the subsolar point, significantly decreasing with increasing solar zenith angle. There is a strong day‐night asymmetry in the external field, with a typical dayside intensity of ∼15–50 nT and a nightside intensity of ∼5–15 nT. Under high solar wind dynamic pressures and IMFs, the external field may be enhanced by a factor of ∼2 everywhere below the BS, on both the dayside and nightside. In addition, our model results suggest that strong crustal fields, which effectively withstand the penetration of the solar wind, reduce the external field at low altitudes. Plain Language Summary: We use nearly 8 years of satellite observations and several global numerical simulations to analyze the average distribution of the external magnetic field induced in the solar wind‐Mars interaction. Our approach is to separate the intrinsic and external components both in field measurements from the MAVEN spacecraft and in simulation results from a global Mars‐solar wind interaction model. The intrinsic crustal magnetic field is rooted beneath the surface and is organized in the rotating, planet‐fixed reference frame. The external magnetic field is better described in a Sun‐Mars reference frame in light of the complex solar wind interaction with the Mars obstacle (combined magnetosphere and ionosphere). Mixing them together results in the appearance of complex magnetic field distributions and affects the understanding of physical processes. Our exclusion of the intrinsic component using a crustal field model enables us to focus on the distribution of the external magnetic field itself, which is relatively poorly understood. We investigate the variability of the external field distribution due to the changes of the upstream solar wind and magnetic field conditions and the ambient crustal field strength. Our work shows that the average external field distribution follows basic patterns despite complex variabilities. Key Points: We use Mars Atmosphere and Volatile EvolutioN observations and magnetohydrodynamic simulations to investigate the external magnetic field environment after the crustal field is excludedThe external field has a typical dayside (nightside) intensity of ∼15–50 nT (∼5–15 nT) and peaks at ∼170 km altitude at the subsolar pointThe external field intensity can be enhanced by a factor of ∼2 on a global scale below the bow shock during high solar activity [ABSTRACT FROM AUTHOR]

Sustainable development is the theme of world economic development in the 21st century. As a key part of sustainable development, sustainable land use (SLU) encompasses economic development and environmentally friendly and social progress. In recent decades, China has formulated many environmental regulatory policies to achieve sustainable development and "carbon peaking and carbon neutrality (double-carbon)" goals, among which the carbon emission trading scheme (CETS) is the most representative and provides valuable research. In this paper, we aimed to reflect the spatio-temporal evolution of SLU in China under the influence of environmental regulatory policies through an indicator measurement strategy based on the DID estimation method. The study conclusions are as follows: (1) The CETS can effectively improve SLU from the perspectives of economic development and environmentally friendly progress, and the impact has primarily been in the pilot areas. And, its effectiveness is closely linked to local locational factors. (2) With respect to the dimension of economic development, the CETS has not changed the provincial distribution patterns of SLU; rather, it continues to remain "high to low, east to west". However, regarding the environmentally friendly progress dimension, the CETS has significantly changed the provincial distribution patterns of SLU, which are characterized by spatial agglomeration with urban agglomerations such as the Pearl River Delta (PRD) and the Yangtze River Delta (YRD) as the core. (3) The screening results of the SLU indicators based on economic development showed that the CETS primarily improved the innovation capacities of pilot regions, and the impacts on economic levels were relatively small. Similarly, the screening results of the SLU indicators based on environmentally friendly progress showed that the CETS had primarily acted on reducing pollution emission intensity and strengthening greening construction, revealing only short-term effects on improving energy use efficiency. Based on the above, this paper explored the meaning and role of the CETS in more detail, with a view to providing insight into the implementation and formulation of environmental regulation policies. [ABSTRACT FROM AUTHOR]

The interaction between Mars and the solar wind results in different plasma regimes separated by several boundaries, among which the separation between the sheath flow and the ionosphere is complicated. Previous studies have provided different and sometimes opposite findings regarding this region. In this study, we utilize observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission to revisit boundaries within this region and perhaps reconcile some differences. More specifically, we start with the photoelectron boundary (PEB), a topological boundary that separates magnetic field lines having access to the dayside ionosphere (open or closed) from those connected to the solar wind on both ends (draped). We find that large gradients in the planetary ion densiti occur across the PEB and that the dominant ion switches from heavy planetary ions to protons near the PEB, indicating that the PEB falls within the ion composition boundary (ICB). Furthermore, our results show that the PEB is not a pressure balance boundary; rather the magnetic pressure dominates both sides of the PEB. Meanwhile, we find that the PEB is located where the shocked solar wind flow stops penetrating deeper into the ionosphere. These findings suggest the PEB marks the top of the Mars dayside ionosphere and also the interface where the sheath plasma flow deflects around the obstacle going downstream. Key Points: Large gradients in planetary ion density occur across the photoelectron boundary (PEB) and the PEB falls within the ion composition boundaryThe PEB can be considered as the top of the Mars dayside ionosphereThe PEB is not a pressure balance boundary but is located where the shocked sheath flow is diverted around the ionosphere [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: 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. Key Points: 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 [ABSTRACT FROM AUTHOR]

This paper represents the first attempt to predict the occurrence location and probability of discrete electron aurora on the nightside of Mars. We run a 3‐D time‐dependent magnetohydrodynamic model to characterize the spatial and temporal dynamics of magnetic field and plasma distributions over the course of one planetary rotation. We perform eight simulation cases under solar minimum quiet‐solar‐wind conditions (four equinox/solstice seasons, each with two interplanetary magnetic field polarities) and in an actual interplanetary coronal mass ejection (ICME) case to assess quiet and space weather situations, respectively. The occurrence of detectable discrete aurora is subject to the combination of the probabilities that (a) the ionosphere is magnetically connected with high altitudes through open field lines and (b) precipitating energy fluxes of >30 eV electrons exceed 0.1 erg/cm2/s. Our results show that during quiet solar activity, discrete aurora occurs likely on small‐scale patches embedded inside strong crustal magnetic field regions (with a magnitude greater than 50 nT at 150 km), and the overall chance across the globe is ∼0.77%. The higher probability over strong crustal field regions is attributed to the stronger magnetic field convergence. Modeling shows the occurrence probability dramatically increases during the ICME event, particularly by more than an order of magnitude in weak crustal field regions. Our model results reasonably agree with NASA Mars Atmosphere and Volatile EvolutioN and Mars Express observations. Our study suggests that nightside discrete electron aurora is not caused by the direct entry of magnetosheath plasma in a cusp‐like process but due to the recycling of nightside magnetospheric electrons. Plain Language Summary: This paper represents the first attempt to predict the occurrence location and probability of discrete electron aurora at Mars on a planetary scale. Discrete aurora is a patchy and sporadic phenomenon, posing a daunting challenge for understanding how and where auroral electron precipitation takes place in the ionosphere. To address this challenge, we apply a state‐of‐the‐art global model to characterize the spatial and temporal dynamics of near‐Mars plasma and magnetic field environments. We simulate the penetration of energetic electrons from high altitudes to the nightside ionosphere through open magnetic field lines, a process responsible for auroral emissions. Our results show that during quiet solar activity, the overall chance of observing a discrete auroral event on the nightside is only ∼0.77% across the globe, but the odds are significantly higher over strong crustal field regions. The occurrence probability is enhanced globally during an extreme space weather event, especially in weak crustal field regions. This study reveals a different source mechanism from the prevailing hypothesis that discrete aurora may be excited by the direct entry of magnetosheath plasma in a cusp‐like process. Instead, we propose that it is caused by the recycling of nightside magnetospheric electrons that return to the ionosphere. Key Points: Modeling shows that discrete aurora occurs more likely on small‐scale patches embedded inside strong crustal field regionsAuroral occurrence probability greatly increases during space weather events, particularly in weak crustal field regionsDiscrete aurora is not caused by the direct entry of magnetosheath plasma but due to the recycling of nightside magnetospheric electrons [ABSTRACT FROM AUTHOR]

The motion of charged particles is governed by electromagnetic forces at high altitudes at Mars and thus the characterization of electrostatic potential and electric fields is important for understanding ion escape at Mars. In this study, we utilize measurements from the Mars Atmosphere and Volatile EvolutioN mission to derive electrostatic potentials above the collisional atmosphere at Mars. We find averaged potentials to be up to ∼100 V in the magnetosheath and down to ∼−70 V in the tail, with respect to the upstream. We then derive electric fields based on averaged potential maps, ranging ∼0.01−0.1 $\sim 0.01-0.1$ V/km. These data‐derived electric fields are in good agreement with ambipolar electric fields from a multi‐fluid magnetohydrodynamic (MHD) model. MHD results also reveal that these large electric fields mainly originate from the electron pressure gradient in the magnetosheath and in the transition region from the hot solar wind flow to the cold ionospheric flow. This work provides the first data‐based characterization of global ambipolar electric fields at Mars (outside of the main ionosphere). Plain Language Summary: The motion of charged particles is governed by electric and magnetic force at high altitudes at Mars and thus the characterization of electric fields is important for understanding ion escape, a form of atmospheric escape, at Mars. In this study, we utilize measurements from the Mars Atmosphere and Volatile EvolutioN mission to derive electric fields at high altitudes, which occur at density and/or temperature gradients in a collisionless plasma to maintain charge neutrality with highly mobile electrons and much slower moving ions. These data‐derived electric fields are in good agreement with electric fields from a magnetohydrodynamic model. Model results also reveal the plasma source of these electric fields. Our characterization of these electric fields provides a better understanding of the interaction between Mars and the Sun and, to a large extent, Mars' atmospheric escape. Key Points: This work provides the first data‐based characterization of global ambipolar electric fields at Mars (outside of the main ionosphere)We find averaged ambipolar potentials ranging from ∼−70 to +100 V and ambipolar electric fields of ∼0.01−0.1 $\sim 0.01-0.1$ V/kmMHD results show a good agreement with data‐derived electric fields and also suggest the plasma source of these ambipolar electric fields [ABSTRACT FROM AUTHOR]

This study provides the first characterization of magnetic topology (i.e., the magnetic connectivity to the collisional ionosphere) at Venus, which might give new insights into the Venusian space environment on topics such as the penetration of the interplanetary magnetic field (IMF) into the ionosphere, planetary ion outflow and inflow, and auroral emission. Magnetic topology is inferred from the electron and magnetic field measurements from Venus Express. We demonstrate through a few case studies that various types of magnetic topologies exist at Venus, including typical draped IMF, open magnetic fields connected to the nightside atmosphere or the dayside ionosphere, and unexpected cross‐terminator closed field lines. We also provide a detailed characterization of an ionospheric hole event, where we find an open topology and a field‐aligned potential of ∼[−10,−20] V with respect to the collisional ionosphere, which has important implications for its formation mechanism. Plain Language Summary: Venus has negligible intrinsic magnetic fields to the first order, such that its ionosphere (the charged part of the atmosphere) interacts directly with the solar wind plasma and magnetic field. Therefore, magnetic connectivity to the ionosphere and/or solar wind is an important piece of information for understanding the near‐Venus space environment and the Sun‐Venus interaction. We utilize measurements from the Venus Express spacecraft to determine magnetic connectivity, or magnetic topology, for the first time. We find three types of magnetic topology at Venus, one of which is unexpected. This study enhances our current understanding of Venus' magnetic configuration and lays the groundwork for a new powerful tool to help understand various topics of the near‐Venus space environment. Key Points: Various types of magnetic topology can be inferred at Venus, including unexpected cross‐terminator closed field linesWe find open magnetic topology and a field‐aligned potential concurring with an ionospheric hole event, hinting at the formation mechanismMagnetic topology can be a new powerful tool to help better understand various topics of the near‐Venus space environment [ABSTRACT FROM AUTHOR]

Longitudinal structures in the Martian thermosphere and topside ionosphere between 150 and 200 km altitudes are studied using in situ electron and neutral measurements from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Four time intervals are selected for comparison, during which MAVEN sampled similar local time (9.3–10.3 h) and latitude (near 20°S) regions but at different solar longitude positions (two near northern summer solstice, one each at northern vernal and autumnal equinoxes). Persistent and pronounced tidal oscillations characterize the ionosphere and thermosphere, whose longitudinal variations in density are generally in‐phase with each other. Our analysis of simultaneous and collocated neutral and electron data provides direct observational evidence for thermosphere‐ionosphere coupling through atmospheric tides. We conclude that the ionosphere is subject to modulation by upward‐propagating thermal tides, via both tide‐induced vertical displacement and photochemical reactions. Atmospheric tides constitute a ubiquitous and significant perturbation source to the ionospheric electron density, up to ∼15% near 200 km.Plain Language Summary: Vertically propagating tides are a type of global‐scale periodic oscillation caused by solar heating in a rotating planetary atmosphere. Martian atmospheric tidal waves have been extensively observed and studied at low altitudes, but our knowledge concerning their behavior at high altitudes is sparse. In particular, little is known about tidal oscillations in the ionosphere, which is the part of the upper atmosphere that is ionized by absorption of solar EUV and X‐ray irradiance. Using in situ neutral and electron measurements from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we investigate thermal tidal signatures in both the Martian upper atmosphere and ionosphere. Our analysis of simultaneous and collocated ionospheric and atmospheric data provides direct observational evidence that the charged and neutral regimes are tightly coupled, not only through well‐understood photochemical reactions but also by tidal waves forced from below. This study elucidates the role of planetary‐scale tidal waves in coupling various elements of the near‐Mars space environment. Besides our directly examined neutral‐electron density coupling, this study also sheds light on the nature of vertical coupling between the lower and upper atmospheric regimes of Mars.Key Points: Direct observational evidence for Martian thermosphere‐ionosphere coupling by atmospheric tides is presentedThe ionosphere below 200 km altitude is controlled by photochemistry and modulated by tide‐induced vertical displacementAtmospheric tides constitute a ubiquitous, significant source of ionospheric electron density variability (up to ∼15% at 200 km altitude) [ABSTRACT FROM AUTHOR]

Large‐scale magnetic fields have been observed in Venus' ionosphere by both the Pioneer Venus Orbiter (PVO) and Venus Express spacecraft. In this study, we examine the formation and evolution of the large‐scale magnetic field in the Venus ionosphere using a sophisticated global multispecies Magnetohydrodynamics (MHD) model that has been developed for Venus (Ma et al., 2013, https://doi.org/10.1029/2012JA018265). A time‐dependent model run is performed under varying solar wind dynamic pressure. Based on model results, we find that (1) the initial response of the induced magnetosphere is fast (~min), (2) a large‐scale magnetic field gradually forms in the ionosphere when the solar wind dynamic pressure suddenly exceeds the ionospheric thermal pressure, (3) both the penetration and decay of the large‐scale magnetic field in the ionosphere are slow (~hr), and (4) the ion escape rate has a nonlinear response to the change of solar wind dynamic pressure. Plain language Summary: Large‐scale magnetic fields have been observed at Venus' ionosphere by previous Venus missions. In this study, we examine the formation and evolution of the large‐scale magnetic field in the Venus ionosphere using a sophisticated global model. A time‐dependent model run is performed under varying solar wind dynamic pressure (density). Model results show that the outside interaction region responds quickly (~min) to the solar wind variation, while the response time of the ionosphere is long (~hr). We also found that the ion escape rate has a nonlinear response to the change of solar wind dynamic pressure. Key Points: The global MHD model self‐consistently reproduces the formation and evolution of the large‐scale magnetic fields in the Venus ionosphereModel results show that it takes quite long time (~hr) for the magnetic field to penetrate into and decay in the ionosphereThe large‐scale magnetic fields in the ionosphere act as an additional obstacle to the solar wind [ABSTRACT FROM AUTHOR]

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)‐CO2 collisions. 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. Key Points: We investigated the effect of dust storms on photochemical escape from Mars using up‐to‐date cross sections for O‐CO2 collisionsThe 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 [ABSTRACT FROM AUTHOR]

Lycopene is considered as a promising neuroprotector with multiple bioactivities, while its therapeutic use in neurological disorders is restricted due to low solubility, instability and limited bioavailability. Our work aimed to develop lycopene-loaded microemulsion (LME) and investigate its potentials in improving bioavailability and brain-targeting efficiency following oral administration. The blank microemulsion (ME) excipients were selected based on orthogonal design and pseudo-ternary phase diagrams, and LME was prepared using the water titration method and characterized in terms of stability, droplet size distribution, zeta potential, shape and lycopene content. The optimized LME encompassed lycopene, (R)-(+)-limonene, Tween 80, Transcutol HP and water and lycopene content was 463.03 ± 8.96 µg/mL. This novel formulation displayed transparent appearance and satisfactory physical and chemical stabilities. It was spherical and uniform in morphology with an average droplet size of 12.61 ± 0.46 nm and a polydispersity index (PDI) of 0.086 ± 0.028. The pharmacokinetics and tissue distributions of optimized LME were evaluated in rats and mice, respectively. The pharmacokinetic study revealed a dramatic 2.10-fold enhancement of relative bioavailability with LME against the control lycopene dissolved in olive oil (LOO) dosage form in rats. Moreover, LME showed a preferential targeting distribution of lycopene toward brain in mice, with the value of drug targeting index (DTI) up to 3.45. In conclusion, the optimized LME system demonstrated excellent physicochemical properties, enhanced oral bioavailability and superior brain-targeting capability. These findings provide a basis for the applications of ME-based strategy in brain-targeted delivery via oral route, especially for poorly water-soluble drugs. [ABSTRACT FROM AUTHOR]

Intrinsic magnetic fields have long been thought to shield planets from atmospheric erosion via stellar winds; however, the influence of the plasma environment on atmospheric escape is complex. Here we study the influence of a weak intrinsic dipolar planetary magnetic field on the plasma environment and subsequent ion escape from a Mars-sized planet in a global three-dimensional hybrid simulation. We find that increasing the strength of a planet's magnetic field enhances ion escape until the magnetic dipole's standoff distance reaches the induced magnetosphere boundary. After this point increasing the planetary magnetic field begins to inhibit ion escape. This reflects a balance between shielding of the Southern hemisphere from 'misaligned' ion pickup forces and trapping of escaping ions by an equatorial plasmasphere. Thus, the planetary magnetic field associated with the peak ion escape rate is critically dependent on the stellar wind pressure. Where possible we have fit power laws for the variation of fundamental parameters (escape rate, escape power, polar cap opening angle, and effective interaction area) with magnetic field, and assessed upper and lower limits for the relationships. [ABSTRACT FROM AUTHOR]

We model expected dynamo currents above, and resulting magnetic field profiles at, InSight's landing site on Mars, including for the first time the effect of electron‐ion collisions. We calculate their diurnal and seasonal variability using inputs from global models of the Martian thermosphere, ionosphere, and magnetosphere. Modeled currents primarily depend on plasma densities and the strength of the neutral wind component perpendicular to the combined crustal and draped magnetic fields that thread the ionosphere. Negligible at night, currents are the strongest in the late morning and near solstices due to stronger winds and near perihelion due to both stronger winds and higher plasma densities from solar EUV photoionization. Resulting surface magnetic fields of tens of nanotesla and occasionally >100 nT may be expected at the InSight landing site. We expect currents and surface fields to vary significantly with changes in the draped magnetic field caused by Mars' dynamic solar wind environment. Plain Language Summary: In the upper atmospheres of planets, solar extreme ultraviolet (EUV) radiation produces ions and electrons. Electric currents flow whenever electrons and ions move differently from each other, due to their opposite charges and different masses. When neutral wind causes this differential motion, it is called a dynamo current. Here we simulate these dynamo currents above the NASA InSight Mars lander, resulting from magnetic and collision forces acting upon ions and electrons in the Martian upper atmosphere. We find that modeled currents primarily depend on (a) the density of electrons and ions and (b) the strength of the neutral wind component that is perpendicular to the combined draped and crustal magnetic field that sits within the Mars ionosphere. Negligible at night, predicted currents are the strongest in the late morning and near solstices, due to stronger winds, and near Mars' closest approach the sun, due to both stronger winds and higher plasma densities from solar EUV photoionization. Resulting surface magnetic fields of tens of nanotesla and occasionally >100 nT may be expected at the landing site. We expect currents and surface fields to vary significantly with changes in the draped magnetic field caused by Mars' dynamic solar wind and space weather environment. Key Points: We model wind‐driven ionospheric dynamo currents and resulting magnetic fields on the Martian surfaceSurface fields of tens to up to 100 nT are predicted during the day, strongest in the late morning and near solstices and perihelionMars' dynamic dayside magnetic field draping leads to significant daily variability in expected strength and direction of surface fields [ABSTRACT FROM AUTHOR]

Abstract: We study a large interplanetary coronal mass ejection event impacting Mars in mid‐September 2017 numerically. During this time period, MAVEN remained inside the Martian bow shock and therefore could not measure the solar wind directly. We first simulate the event using three steady state cases with estimated solar wind conditions and find that these cases were able to reproduce the general features observed by MAVEN. However, these time‐stationary runs cannot capture the response of the system to large variations in the solar wind associated with the event. To address this problem, we derive a solar wind proxy based on MAVEN observations in the sheath region and their comparison with steady state magnetohydrodynamic model results. The derived solar wind proxy is then used to drive a time‐dependent magnetohydrodynamic model, and we find that the data‐model comparison is greatly improved, especially in the magnetosheath. We are able to reproduce some detailed structures observed by MAVEN during the period, despite the lack of a direct measurement of the solar wind, indicating that the derived solar wind conditions are reliable. Finally, we examine in detail the impact of the event on the Martian system: including variations of the three typical plasma boundaries and the ion loss rates. Our results show that these plasma boundary locations varied drastically during the event, and the total ion loss rate was enhanced by more than an order of magnitude. [ABSTRACT FROM AUTHOR]

Abstract: Many aspects of the Sun‐Mars interaction have been investigated during solar transient events with measurements from multiple spacecrafts and also simulation efforts. Limited discussion has been paid to magnetic topology response to disturbed upstream conditions. The implications of topology changes include, but are not limited to, the pattern of energetic particle precipitation into the Martian atmosphere and the impact on cold ion escape during solar transient events as low‐energy ion escape is dependent on magnetic topology. In this study, we investigate the magnetic topology response to the 2017 September interplanetary coronal mass ejection (ICME) event with measurements collected by the Mars Atmospheric and Volatile EvolutioN spacecraft. It is found that the interface between draped interplanetary magnetic field and closed field lines was moved from 800–1400 km in altitude during quiet conditions to 200–400 km after ICME arrived at Mars and then relaxed back to high altitudes again after the event. To gain insight into magnetic topology response on a global scale, we first validate magnetic topology from a time‐dependent simulation with a single‐fluid multispecies magnetohydrodynamic (MHD) model by comparing magnetic topology determined from Mars Atmospheric and Volatile EvolutioN data, which shows a good agreement. Then we present MHD predictions of global magnetic topology changes during this ICME event. In addition to a deeper interplanetary magnetic field penetration, MHD results suggest more open field lines in response to the ICME event. [ABSTRACT FROM AUTHOR]

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 cold thermosphere 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 cold thermospheric oxygen atom, however, is demonstrated to be the primary neutral source for O+ ion escape during the relatively weak solar cycle 24. Key Points: 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 [ABSTRACT FROM AUTHOR]

Abstract: Measurements provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed to investigate the Martian magnetotail configuration as a function of interplanetary magnetic field (IMF) BY. We find that the magnetotail lobes exhibit a ~45° twist, either clockwise or counterclockwise from the ecliptic plane, up to a few Mars radii downstream. Moreover, the associated cross‐tail current sheet is rotated away from the expected location for a Venus‐like induced magnetotail based on nominal IMF draping. Data‐model comparisons using magnetohydrodynamic simulations are in good agreement with the observed tail twist. Model field line tracings indicate that a majority of the twisted tail lobes are composed of open field lines, surrounded by draped IMF. We infer that dayside magnetic reconnection between the crustal fields and draped IMF creates these open fields and may be responsible for the twisted tail configuration, similar to what is observed at Earth. [ABSTRACT FROM AUTHOR]

Abstract: Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observations show clear evidence of the occurrence of the magnetic reconnection process in the Martian plasma tail. In this study, we use sophisticated numerical models to help us understand the effects of magnetic reconnection in the plasma tail. The numerical models used in this study are (a) a multispecies global Hall‐magnetohydrodynamic (HMHD) model and (b) a global HMHD model two‐way coupled to an embedded fully kinetic particle‐in‐cell code. Comparison with MAVEN observations clearly shows that the general interaction pattern is well reproduced by the global HMHD model. The coupled model takes advantage of both the efficiency of the MHD model and the ability to incorporate kinetic processes of the particle‐in‐cell model, making it feasible to conduct kinetic simulations for Mars under realistic solar wind conditions for the first time. Results from the coupled model show that the Martian magnetotail is highly dynamic due to magnetic reconnection, and the resulting Mars‐ward plasma flow velocities are significantly higher for the lighter ion fluid, which are quantitatively consistent with MAVEN observations. The HMHD with Embedded Particle‐in‐Cell model predicts that the ion loss rates are more variable but with similar mean values as compared with HMHD model results. [ABSTRACT FROM AUTHOR]

Abstract: Global models of the interaction of the solar wind with the Martian upper atmosphere have proved to be valuable tools for investigating both the escape to space of the Martian atmosphere and the physical processes controlling this complex interaction. The many models currently in use employ different physical assumptions, but it can be difficult to directly compare the effectiveness of the models since they are rarely run for the same input conditions. Here we present the results of a model comparison activity, where five global models (single‐fluid MHD, multifluid MHD, multifluid electron pressure MHD, and two hybrid models) were run for identical conditions corresponding to a single orbit of observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We find that low‐altitude ion densities are very similar across all models and are comparable to MAVEN ion density measurements from periapsis. Plasma boundaries appear generally symmetric in all models and vary only slightly in extent. Despite these similarities there are clear morphological differences in ion behavior in other regions such as the tail and southern hemisphere. These differences are observable in ion escape loss maps and are necessary to understand in order to accurately use models in aiding our understanding of the Martian plasma environment. [ABSTRACT FROM AUTHOR]

The magnetic field draping pattern in the magnetosheath of Mars is of interest for what it tells us about both the solar wind interaction with the Mars obstacle and the use of the field measured there as a proxy for the upstream interplanetary magnetic field (IMF) clock angle. We apply a time-dependent, global magnetohydrodynamic model toward quantifying the spatial and temporal variations of the magnetic field draping direction on the Martian dayside above 500-km altitude. The magnetic field and plasma are self-consistently solved over one Mars rotation period, with the dynamics of the field morphology considered as the result of the rotation of the crustal field orientation. Our results show how the magnetic field direction on the plane perpendicular to the solar wind flow direction gradually departs from the IMF as the solar wind penetrates toward the obstacle and into the tail region. This clock angle departure occurs mainly inside the magnetic pileup region and tailward of the terminator plane, exhibiting significant dawn-dusk and north-south asymmetries. Inside the dayside sheath region, the field direction has the greatest departure from the IMF-perpendicular component direction downstream of the quasi-parallel bow shock, which for the nominal Parker spiral is over the dawn quadrant. Thus, the best region to obtain an IMF clock angle proxy is within the dayside magnetosheath at sufficiently high altitudes, particularly over subsolar and dusk sectors. Our results illustrate that the crustal field has only a mild influence on the magnetic field draping direction within the magnetosheath region. [ABSTRACT FROM AUTHOR]

With electron and magnetic field data obtained by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we have identified closed magnetic field lines, with both foot points embedded in the dayside ionosphere, extending up to 6,200 km altitude into the Martian tail. This topology is deduced from photoelectrons produced in the dayside ionosphere being observed traveling both parallel and antiparallel to the magnetic field. At trapped-zone pitch angles (within a range centered on 90° where electrons magnetically reflect before interacting with the atmosphere), cases with either solar wind electrons or photoelectrons have been found, indicating different formation mechanisms for these closed loops. These large closed loops are present in MHD simulations. The case with field-aligned photoelectrons mixed with solar wind electrons having trapped-zone pitch angles is likely to be associated with reconnection, while the case with photoelectrons at all pitch angles is probably due to closed field lines being pulled tailward by the surrounding plasma flow. By utilizing an algorithm for distinguishing photoelectrons from solar wind electrons in pitch angle-resolved energy spectra, we systematically map the spatial distribution and occurrence rate of these closed magnetic loops over the region sampled by the MAVEN orbit. We find that the occurrence rate ranges from a few percent to a few tens of percent outside of the optical shadow and less than one percent within the shadow. These observations can be used to investigate the general magnetic topology in the tail, which is relevant to cold ion escape, reconnection, and flux ropes. [ABSTRACT FROM AUTHOR]

This article presents recent progress in understanding solar wind–Mars interaction using a sophisticated global magnetohydrodynamic (MHD) model. Mars has localized crustal magnetic fields, so the solar wind plasma flow interacts directly with the Mars atmosphere/ionosphere system. Such an interaction generates an induced current in the ionosphere, modifies the magnetic field environment around Mars, and more importantly, causes the erosion of the Mars atmosphere. The nonuniformly distributed crustal magnetic field also plays an important role in the interaction process, which is modulated by planetary rotation. Recent advances in computing power allow the inclusion of the continuous crustal field rotation in the simulation with a time-dependent MHD model. Model results have been validated with observations from previous and ongoing Mars missions. The validated time-dependent MHD model is useful in quantifying the variation of ion loss rates with planet rotation and the internal response time scale of the Martian ionosphere. [ABSTRACT FROM PUBLISHER]