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The simulation results for the case of 180. The columns from left to right are cuts in the planes z=0, y=0 and x=4R L . The rows from top to bottom represent the magnitudes of the number density, magnetic field, pressure, velocity and temperature of solar plasma, respectively.
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We study the interaction between the Moon and the solar wind through a three-dimensional MHD simulation. Three cases have been discussed in which the interplanetary magnetic field lies at 90°, 180°, and 135° to the solar wind flow, respectively. A wake with low density and low pressure can always be formed behind the Moon. The plasma temperature an...
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Citations
... The Moon represents an airless body with no global magnetic field nor significant atmosphere, where solar wind can directly interact with the lunar surface. While a small part of the solar wind protons are reflected from the surface (0.1%-1% as H + - Saito et al. 2008; and 10%-20% as energetic neutral atoms, or ENAs- Wieser et al. 2009;Futaana et al. 2012), most solar wind particles are implanted into the surface, leaving a plasma cavity downstream from the Moon (Xie et al. 2012). These implanted solar wind particles can alter the physical and compositional properties of the lunar surface and result in a space-weathering process of the surface (Pieters & Noble 2016). ...
... The global features of the solar wind interaction with the Moon can be reproduced by either an MHD model (Xie et al. 2012) or a hybrid model (Holmstrom et al. 2012). Nevertheless, the interaction between the solar wind and magnetic anomalies has a scale smaller than the ion gyroradius or ion inertial length, in which the fluid assumption is invalid. ...
The solar wind can directly interact with the lunar surface and provide an important source for surface space weathering and water generation. Here we study the solar wind implantation flux on the lunar surface with global Hall MHD simulations. The shielding effects of both the Earth’s magnetosphere and lunar magnetic anomalies are considered. It is found that a large-scale lunar mini-magnetosphere can be caused by the solar wind interaction with the magnetic anomalies on the lunar far side, which causes a large shielding area on the surface. In addition, the Earth’s magnetosphere brings a longitudinal variation in the implantation flux, with minimum fluxes at 0° longitude. With the integrated flux over a lunation, we find that there are some local cavities on the implantation flux map, which are colocated with both the magnetic anomalies and the lunar swirls. Further studies show that there is a south–north asymmetry in the implantation flux, which can be used to explain the lower water content observed in the southern hemisphere. Our results provide a global map of the solar wind implantation flux on the lunar surface and are useful for evaluating the large-scale effect of solar wind implantation and sputtering on the space weathering and the water or gas generation of the surface.
... The solar wind interaction of the Moon, in fact, consists of processes across multiple plasma scales, and that is why the Moon's space environment and solar wind interaction are complicated. From a global view, i.e., discussing the interaction of the whole Moon in a fluid regime of plasma may be appropriate because the scale is over 3,000 km, larger than any featured scales of the solar wind [14,18,19]. When studying the internal structures of the lunar wake with scales comparable with the ion gyroradii, we may adopt 2-fluid plasma theory [14]. ...
Key questions on solar wind–Moon interaction are reviewed. As the nearest celestial body to Earth, Moon’s space environment is distinctive to Earth’s mainly because of lack of a significant atmosphere/ionosphere and a global magnetic field. From a global respective, solar wind can bombard its surface, and the solar wind materials cumulated in the soil record the evolution of the Solar System. Many small-scale remanent magnetic fields are scattered over the lunar surface and, just as planetary magnetic fields protect planets, they are believed to divert the incident solar wind and shield the local lunar surface beneath, thus producing unique local surface environment that is critical to activities of human beings/facilities, thus providing unique landing sites to explore the origins of lunar swirls and remanent magnetic fields. Evidences have hinted that this local interaction, however, may be also distinct with the interacting scenario on planets, and the specific process has not been revealed because of lack of in situ observations in the near-Moon space or on the ground. The global and local solar wind interactions of the Moon represent 2 types of characteristic interaction of celestial bodies with stellar wind in deep space, i.e., the interactions of nonmagnetized bodies and of small-scale magnetized bodies, both of which may occur on asteroids and Mars. The deep-space celestial bodies, either difficult or impossible to reach for human beings or artificial satellites, are hard to measure, and the exploration of the Moon can reveal the mystery of stellar wind interaction on these bodies.
... On a macroscopic scale, a plasma sheath can be formed near the surface with a thickness determined by the Debye length, and then the dust grain can be accelerated in the sheath and transported to a larger distance (Nitter et al. 1998;Stubbs et al. 2006;Li et al. 2019;Xie et al. 2020). Furthermore, most solar wind ions can be obstructed and absorbed on the dayside, leaving a plasma wake downstream of the body (Xie et al. 2013;Zimmerman et al. 2014). ...
... Different models are needed for the interactions with different sizes. When the characteristic size of the interaction is 1 order of magnitude larger than the ion gyroradius (>1000 km), such as the Moon and some strongly magnetized asteroid, an MHD model is appropriate (Baumgartel et al. 1994;Xie et al. 2013;Anand et al. 2021). When the characteristic size is comparable to the ion gyroradius (∼100 km), such as some large asteroids and weakly magnetized asteroids, a hybrid model can be used (Omidi et al. 2002;Lindkvist et al. 2017;Fatemi & Poppe 2018). ...
... Such a self-similar plasma expansion model was used to explain the density drop and the ion acceleration in the lunar wake (Ogilvie et al. 1996;Halekas et al. 2005). However, later observations and numerical simulations showed that the rarefaction wave in the lunar wake actually propagated via fast magnetosonic mode since the scale of the lunar wake was so large that both the ions and the electrons are magnetized (Holmström et al. 2012;Zhang et al. 2012;Xie et al. 2013). Recently, Zimmerman et al. (2014) found that the plasma wake caused by the solar wind interaction with a small asteroid had a cone angle approximately equal to the angle predicted by the self-similar plasma expansion theory, known as θ i = arctan(C s /V sw ). ...
The recently discovered asteroid 2016 HO 3 is the most stable quasi-satellite of our Earth. Several missions to 2016 HO 3 have been proposed, including the Tianwen-2 mission of China. Here we study the solar wind interaction with 2016 HO 3 with three-dimensional particle-in-cell simulations. It is found that the sunlit surface can be positively charged to more than +10 V, and the shadowed surface is negatively charged to lower than −30 V. The typical electric field on the sunlit surface is about 2 V m ⁻¹ but can increase up to 20 V m ⁻¹ near the terminator. There is a plasma wake behind 2016 HO 3 with a reduced plasma density. Normally, the ion density can be reduced to about 0.3 of the solar wind density at 100 m downstream from 2016 HO 3 , and the plasma wake is confined by a Mach cone with a cone angle of about 6.°5. In addition, we find that both the solar wind parameters and the secondary electron emission can affect the surface charging, which, in return, changes the wake structure.
... Past studies of the lunar wake have shown the formation of correlated drops in density and magnetic field associated with fast magnetosonic rarefaction wakes (e.g. Fatemi et al., 2013;Holmström et al., 2012;Xie et al., 2012). The formation of Alfvén wings in the lunar wake has also been suggested by Zhang et al. (2016). ...
When in the solar wind, the Moon is exposed to its embedded discontinuities such as interplanetary (IP) shocks. In this study we utilize 3‐D electromagnetic hybrid (kinetic ions, fluid electrons) simulations and observations of two events, by THEMIS/ARTEMIS spacecraft to understand the interaction of IP shocks with the Moon. Simulation parameters are based on one of the ARTEMIS events and include the presence of supra‐thermal ions in the solar wind. The results show that the absorption of the cold solar wind protons on the Moon's dayside leads to a density hole in the shock front behind the Moon. This density hole refills and recovers as the IP shock moves down the lunar tail. Penetration of the interplanetary magnetic field through Moon's body leads to the survival of a steepened magnetic structure associated with the shock surface. However, due to the lower pressures in the lunar tail the structure broadens in space and is expected to steepen when the IP shock is beyond the tail. The IP shock is also found to interact with the energetic ions in the lunar tail resulting in their acceleration to higher energies. Comparing the densities measured by ARTEMIS in the solar wind and lunar tail shows the absence of a shock front in density in the tail consistent with the formation of a density hole at the shock front. Similarly, comparing the magnetic field profiles in the solar wind and lunar tail shows the expected broadening of the magnetic field shock front.
... Numerous particle-in-cell (PIC) and hybrid PIC simulations of the steady flow past the Moon also reveal the presence of these downstream disturbances (Farrell et al. 1998;Birch & Chapman 2001;Wang et al. 2011;Fatemi et al. 2012Fatemi et al. , 2013Holmström et al. 2012;Poppe et al. 2014;Rasca et al. 2021). There are also several modeling studies focusing on the lunar wake structure under nominal solar wind conditions using MHD descriptions (Spreiter et al. 1970;Cui & Lei 2008;Xie et al. 2013;Michel 2014) as well as particle (Farrell et al. 1998;Birch & Chapman 2001;Nakagawa 2013) and hybrid PIC models (Wang et al. 2011;Fatemi et al. 2012Fatemi et al. , 2013Holmström et al. 2012;Vernisse et al. 2013;Poppe et al. 2014). ...
In the solar wind, a low-density wake region forms downstream of the nightside lunar surface. In this study, we use a series of 3D hybrid particle-in-cell simulations to model the response of the lunar wake to a passing coronal mass ejection (CME). Average plasma parameters are derived from the Wind spacecraft located at 1 au during three distinct phases of a passing halo (Earth-directed) CME on 2015 June 22. Each set of plasma parameters, representing the shock/plasma sheath, a magnetic cloud, and plasma conditions we call the mid-CME phase, are used as the time-static upstream boundary conditions for three separate simulations. These simulation results are then compared with results that use nominal solar wind conditions. Results show a shortened plasma void compared to nominal conditions and a distinctive rarefaction cone originating from the terminator during the CME’s plasma sheath phase, while a highly elongated plasma void reforms during the magnetic cloud and mid-CME phases. Developments of electric and magnetic field intensification are also observed during the plasma sheath phase along the central wake, while electrostatic turbulence dominates along the plasma void boundaries and 2–3 lunar radii R M downstream in the central wake during the magnetic cloud and mid-CME phases. The simulations demonstrate that the lunar wake responds in a dynamic way with the changes in the upstream solar wind during a CME.
... The fluxes near 180°in both Figures 3(c) and (d) indicate that a significant portion of the refilling ions were moving backwards from the downstream wake. This could result from the pressure gradient between the intermediate wake and the near wake, which has been reported in simulation (Xie et al. 2013) and in observations (Zhang et al. 2016) in the solar wind. In comparison, the rapid refilling electrons are almost isotropic (Figure 3(g)). ...
The lunar wake is usually rapidly refilled when the background plasma is substantially subsonic. Here we present observational case studies, by the two ARTEMIS spacecraft, of the lunar wakes in the magnetosheath near the magnetopause under transonic plasma flows with relatively large plasma beta and different magnetic field orientations. The associated background plasma betas are near 1, suggesting that the plasmas are not strongly controlled by the magnetic fields. As a result, the part of the lunar wake under subsonic plasma was rapidly refilled. Pitch angle distributions reveal that a significant portion of the refilling ions are from the downstream wake. This is consistent with the fact that higher sound speed than bulk speed of the background plasma enables downstream particles to get access to upstream wake due to the pressure gradient. The other part under supersonic plasma remains a typical wake structure with high plasma density or flux depletions. Our results show that the Mach number and plasma beta primarily determine the rapid refilling of the lunar wake, which is allowed only in subsonic plasma with plasma beta greater than or close to 1 and hardly influenced at all by the magnetic field orientation.
... on the lunar wake structure under nominal solar wind conditions using magnetohydrodynamic (MHD) descriptions (e.g., Cui & Lei, 2008;Spreiter et al., 1970;Xie et al., 2013) as well as particle (e.g., Birch & Chapman, 2001;Farrell et al., 1998) and hybrid models (e.g., Fatemi et al., 2012Fatemi et al., , 2013Holmström et al., 2012;Poppe et al., 2014;Wang et al., 2011). Moreover, the refilling process is affected by extreme events such as solar storms that alter the interplanetary magnetic field (IMF) and plasma properties/composition of the solar wind. ...
Under nominal solar wind conditions, a tenuous wake forms downstream of the lunar nightside. However, the lunar plasma environment undergoes a transformation as the Moon passes through the Earth's magnetotail, with hot subsonic plasma causing the wake structure to disappear. We investigate the lunar wake response during a passing coronal mass ejection (CME) on March 8, 2012 while crossing the Earth's magnetotail using both a magnetohydrodynamic (MHD) model of the terrestrial magnetosphere and a three‐dimensional hybrid plasma model of the lunar wake. The CME arrives at 1 AU around 10:30 UT and its impact is first detected inside the geomagnetic tail after 11:10 UT by the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (THEMIS‐ARTEMIS) satellites in lunar orbit. A global magnetospheric MHD simulation using Wind data for upstream conditions with the OpenGGCM model reveals the magnetosheath compression to the lunar position from 11:20–12:00 UT, accompanied by multiple flux rope or plasmoid‐like features developing and propagating tailward. MHD results support plasma changes observed by the THEMIS‐ARTEMIS satellites. Lunar‐scale simulations using the Amitis hybrid code show a short and misaligned plasma wake during the Moon's brief entry into the magnetosheath at 11:20 UT, with plasma expansion into the void being aided by the higher plasma temperatures. Sharply accelerated flow speed and a compressed magnetic field lead to an enhanced electric field in the lunar wake capable of generating sudden changes to the nightside near‐surface electric potential.
... The global features of the lunar wake and their dependence on the solar wind conditions have been investigated by different numerical modeling, including Vlasov simulations (e.g., Umeda et al. 2011), magnetohydrodynamic simulations (e.g., Xie et al. 2013), and hybrid simulations (e.g., Holmström et al. 2012;Fatemi et al. 2013). Poppe et al. (2014) made a comparative study between hybrid simulations and the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun mission (ARTEMIS) observations of extreme diamagnetic field in the lunar wake when the background plasma beta exceeds 10, the magnetic field strengths in the lunar wake are found to increase to 230% and 250% of the ambient IMF strength. ...
Because of the plasma pressure gradient across the lunar wake boundary, the interplanetary magnetic field is
enhanced in the lunar wake. In previous works, the solar wind ions that enter into the near lunar wake are found to
have an unimportant influence on the magnetic field within the lunar wake. In this study, two cases of a 22%–70%
reduction of the magnetic field in the near lunar wake are first observed by the Acceleration, Reconnection,
Turbulence and Electrodynamics of the Moon’s Interaction with the Sun mission (ARTEMIS). The magnetic field
depressions are caused by the refilling of dense plasma clouds (with densities of 0.20–0.47 cm−3
) into the near
lunar wake. The ions of the plasma clouds that originate from the reflected solar wind ions in the lunar dayside are
accelerated into the near lunar wake by the solar wind convection electric field. The source regions of the reflected
ions can be traced back to the lunar magnetic anomalies over the sunlit surface. Pressure (magnetic pressure +
thermal pressure) balances are roughly maintained for both cases at the boundary between the plasma cloud and the
ambient plasma. Our results imply that the interaction between the solar wind and lunar magnetic anomalies
drastically disturbs the near-Moon electromagnetic environment
... Solar wind pours out in space roughly 10 9 kg/s or one million tonnes of charged particles per second, within an energy range 1.5-10 keV and speed %250-750 km/s (Meyer-Vernet, 2007). Interaction between solar wind and planetary objects explains how the structure, composition, chemistry, and energy change in theses environments (El-Labany et al., 2006;Xie et al., 2013;Popel et al., 2013;Popel et al., 2015;Popel and Morozova, 2017;Lakhina and Singh, 2015;Sreeraj et al., 2018;Moslem et al., 2018). Of particular interest is the atmospheric escape from planets without a global magnetic field. ...
The nature of ionospheric losses from Venus is of essential importance for understanding the ionosphere dynamics of this unmagnetized planet. A plausible mechanism that can explain the escape of charged particles involves the solar wind interaction with the upper atmospheric layers of Venus. The hydrodynamic approach proposed for plasma expansion in the present study comprises two populations of positive ions and the neutralizing electrons, which interact with the solar wind electrons and protons. The fluid equations describing the plasma are solved numerically using a self-similar approach. The behavior of plasma density, velocity, and electric potential, as well as their reliance upon solar wind parameters have been examined. It is found that for noon midnight sites, the oxygen ion-to-electron relative density may be the main factor to enhance the ionic loss. However, the other parameters, like hydrogen density and solar wind density and velocity seem to do not stimulate the runaway ions. For lower dawn-dusk region, the plasma are composed of hydrogen and oxygen ions as well as electrons, but for higher altitudes only hydrogen ions and electrons are encountered. All ionic densities play an important role either to reduce or boost the ionic loss. The streaming solar wind velocity has no effect on the plasma escaping for lower altitudes, but it reduces the expansion at higher altitudes.
... This result is different from the previous study in the solar wind ( Zhang et al. 2016) and that obtained at Rhea (Simon et al. 2012). The reasons for this could be that the magnetic field was almost flow-aligned, and that the pressure gradient along the wake direction ( Xie et al. 2013;Zhang et al. 2016) did not exist in this event. ...
Typical lunar wakes are usually formed in the supersonic background plasma in the solar wind or distant magnetosheath because the plasmas do not have enough time to refill into the wake with thermal velocities. Here we present ARTEMIS observations of a well-structured lunar wake under subsonic plasma near the Earth’s magnetopause, where the background plasma flows are nearly field-aligned and have relatively low plasma beta. This lunar wake is quite different from the typical lunar wakes in the supersonic solar wind. The boundaries of this lunar wake are clearly outside the boundaries of the optical shadow, indicating that there is no gradual refilling of ambient plasma into the wake. Meanwhile, no enhancement of magnetic strength in the lunar wake is evident for the absence of diamagnetic currents at the boundaries of the lunar wake. The significantly strong gradient of plasma pressure at the wake boundary cannot be maintained under the subsonic condition because the rarefaction wake can propagate upstream and thus the Mach cone outside the wake will disappear so that the upstream plasma pressure supplement will decrease. Our results also show that the very low plasma beta plays a crucial role in the formation of the lunar wake in subsonic plasma.
