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Abstract As a weakly magnetized planet, Mars interacts directly with the highly variable solar wind, where small-scale and short-duration structures are ubiquitous. Among solar wind parameters, dynamic pressure, as the dominant external pressure, plays a key role in shaping the pressure level and structures in the downstream induced magnetosphere. In this study, a multispecies global magnetohydrodynamic model is used to investigate Mars’s response to a series of idealized solar wind dynamic pressure enhancements with varying durations and magnitudes, aiming to capture responses in different plasma regions and isolate the effects of dynamic pressure. For the subsolar region, the simulations reveal a sequence of response phases, each exhibiting distinct temporal characteristics. Beyond the subsolar region, the terminator ionosphere and global ion escape show prolonged disturbances. These results highlight the importance of short-term upstream variability in shaping both local and global features of the Martian plasma environment and provide context for interpreting spacecraft observations that sample only limited regions of the system. 

Abstract Using the latest Mars Multi‐fluid Magneto‐hydrodynamic (MHD) model (Y. J. Ma et al., 2019,https://doi.org/10.1029/2019ja027091), we examined an extremely low solar wind density event observed by Mars Atmosphere and Volatile Evolution (MAVEN) on 26 December 2022. Simulation results show that the solar wind density plays a crucial role in plasma interactions. The interaction region expands significantly from less than 2 R_Munder typical solar wind density conditions to more than 4 R_Malong the subsolar line for extremely low solar wind density (<0.1 cm⁻³), consistent with MAVEN observations during the event. Under low solar wind density conditions, the ion pickup plume becomes smaller and is associated with a lower flow speed. Model results also show a nonlinear correlation between the solar wind density and the ion escape rates. Specifically, when the solar wind density is relatively high (>0.2 cm⁻³), the total ion loss rate positively correlates with the solar wind density. However, when the solar wind density is extremely low, ion escape rates are nearly constant despite further decreases in solar wind density. For this event, the solar wind density dropped by over an order of magnitude, while the MHD model predicts the total ion escape rate reduced by approximately a factor of ∼3. Additionally, we investigated possible reasons for the sudden drop in magnetic field strength during the inbound segment of two consecutive orbits and found that a sudden change of the interplanetary magnetic field direction to radial configuration could also attribute to the observed field decrease. 

This perspective article discusses the knowledge gaps and open questions regarding the solar and interplanetary drivers of space weather conditions experienced at Mars during active and quiescent solar periods, and the need for continuous, routine observations to address them. For both advancing science and as part of the strategic planning for human exploration at Mars by the late 2030s, now is the time to consider a network of upstream space weather monitors at Mars. Our main recommendations for the heliophysics community are the following: 1. Support the advancement for understanding heliophysics and space weather science at ∼1.5 AU and continue the support of planetary science payloads and missions that provide such measurements. 2. Prioritize an upstream Mars L1 monitor and/or areostationary orbiters for providing dedicated, continuous observations of solar activity and interplanetary conditions at ∼1.5 AU. 3. Establish new or support existing 1) joint efforts between federal agencies and their divisions and 2) international collaborations to carry out #1 and #2. 

This white paper is on the HMCS Firefly mission concept study. Firefly focuses on the global structure and dynamics of the Sun's interior, the generation of solar magnetic fields, the deciphering of the solar cycle, the conditions leading to the explosive activity, and the structure and dynamics of the corona as it drives the heliosphere.