Charge exchange between solar wind protons and local hydrogen atoms generates hydrogen energetic neutral atoms (H-ENAs) in the extended neutral hydrogen corona surrounding Mars. The following collisions between H-ENAs and atmospheric molecules generate a distinct proton aurora. How the solar wind influences the proton aurora activity in the short term is not well unknown. We found that there are synchronized proton aurora brightening and atmospheric ion loss intensifying on Mars, both controlled by solar wind dynamic pressure, using observations by the Mars Atmosphere and Volatile Evolution spacecraft. Significant erosion of the Martian ionosphere during periods of high dynamic pressure indicates at least five-to-tenfold increase in atmospheric ion loss. An empirical relationship between ion escape rate and auroral emission enhancement is established, providing a new proxy of Mars’ atmospheric ion loss with optical imaging that may be used remotely and with greater flexibility.

The absence of a global magnetic field at Mars results in a direct interaction between the solar wind and the ionosphere, leading to ion escape from its atmosphere to space. However, the existence and asymmetric distribution of crustal fields introduce significant complexity into the plasma dynamics within the Martian environment, resulting from a disordered magnetic field topology characterized by its orientation parallel, directed towards, and away from the Martian surface. Based on three-dimensional multifluid magnetohydrodynamic simulations, we investigated the impact of the magnetic inclination angle on the Martian ionospheric plasma dynamics under the typical solar wind conditions. Numerical results showed that ions can be effectively diffuse upwards along vertical magnetic fields driven by the electron pressure gradient and the motional electric force, leading to a strong outward flux escaped through plume and the magnetotail eventually. In addition, due to the Hall electric force, there is a tendency for ion flow to be deflected in the horizontal plane. These results provide valuable insights into the influence of magnetic fields on ion motion in the Martian space environment.

Context. Highly variable ionospheric structures were recently detected on Mars using spacecraft measurements. Acoustic-gravity waves (AGWs) could be the underlying mechanism. Studying the response of the Martian ionosphere to AGWs could provide us with an important understanding of the neutral wave-ionospheric coupling processes. Aims. We developed a linearized wave model to explore the plasma-neutral coupling driven by AGWs in the lower ionosphere of Mars. This model can describe the propagation and dissipation of AGWs in a realistic atmosphere and is the first of its kind to incorporate plasma behaviors associated with photochemistry and electromagnetic fields. Methods. We adopted a full-wave model as the first part of our coupled model to delineate wave propagation in a realistic atmosphere. The second part of our model consists of the governing equations describing the plasma behaviors. Therefore, our model not only replicates the result of the full-wave model, but can also be used to investigate the wave-driven variations in the plasma velocity and density, electromagnetic field, and thermal structures. Results. Our model results reveal that ions are mainly dragged by neutrals and oscillate along the wave phase line below similar to 200 km altitude. Electrons are primarily subject to gyro-motion along the magnetic field lines. The wave-driven distinct motions among charged particles can generate the perturbed electric current and electric field, further contributing to localized magnetic field fluctuations. Major charged constituents, including electrons, O+, O-2(+), and CO2+, have higher density amplitudes when interacting with waves of larger periods. The presence of photochemistry leads to a decrease in the plasma density amplitude, and there exists a moderate correlation between the density variations of plasma and those of neutrals. Our numerical results indicate that the wave-driven variations range from several percent to similar to 80% in the plasma density and from similar to 0.2% to 17% in the magnetic field, values that are consistent with the spacecraft observations. Further calculations reveal that the wave-induced plasma-neutral coupling can heat the neutrals yet cool the plasmas. Electrons are cooler than ions in the coupling process. The wave-driven heating by neutral-ion collisions exceeds that by neutral-electron collisions but tends to be lower than the wave dissipative heating and photochemical heating. Our model has potential applications in studying the AGW-driven variable ionospheric structures and can be used for other planets.

In steady state, magnetic flux conservation must be maintained in Saturn’s magnetosphere. The Enceladus plumes add mass to magnetic flux tubes in the inner magnetosphere, and centrifugal force pulls the mass‐loaded flux tubes outward. Those flux tubes are carried outward to the magnetotail where they deposit their mass and return to the mass loading region. It may take days for the magnetic flux to be carried outward to the tail, but the return of the nearly empty flux tubes can last only several hours, with speeds of inward motion around 200 km/s. Using time sequences of Cassini particle count rate, the difference in curvature drift and gradient drift is accounted for to determine the return speed, age, and starting dipole L‐shell of return flux tubes. Determination of this flux‐return process improves our understanding of the magnetic flux circulation at Saturn and provides insight into how other giant planets remove the mass added by their moons.

The induced magnetotails on Mars and Venus are considered to arise through the interplanetary magnetic field (IMF) draping around the planet and the solar wind deceleration due to the mass loading effect. They have very similar structures as that on Earth, two magnetic lobes of opposite radial magnetic fields and a plasma sheet in between. However, the orientation and geometry of the induced magnetotails are controlled by the IMF, not the planetary intrinsic magnetic field. In this study, we present another characteristic of the induced magnetotails on Mars and Venus with the observations of MAVEN and Venus Express. It is found that the magnetic flux in the induced magnetotails on Mars and Venus are inhomogeneous. There is more magnetic flux in the +E hemisphere than -E hemisphere. The magnetic flux is observed to transport gradually from the +E hemisphere to the -E hemisphere along the magnetotail. The magnetotail magnetic flux transport seems to be faster on Mars than that at Venus. Based on these observations, we suggest that the finite gyro-radius effect of the planetary ions that are picked up by the solar wind is responsible to the magnetic flux inhomogeneity and transport in the induced magnetotails. The role of the magnetic pressure gradient in the magnetotail will be discussed.