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A unique event known as the disappearing solar wind (DSW), characterized by an extremely low-density solar wind stream, occurred at Mars on 2022 December 26–27. As this stream flowed past Mars, several properties of the Mars–solar wind interaction changed in response to the density drop. We utilize in situ plasma measurements from the Mars Atmosphere and Volatile EvolutioN spacecraft to examine heavy ion escape during this event. We find that escaping ions with energies above and below 30 eV responded differently to the reduction in solar wind density. High-energy ions experienced a decrease in flux, whereas low-energy ions experienced an increase, regardless of whether they were escaping through the plume or tailward channel. Furthermore, we observe a net reduction in the flux of plume escaping ions during the DSW period, primarily due to a considerable reduction in the high-energy component, which typically dominates plume escape. In contrast, the overall flux of tailward escaping ions increased during this period. These variations in heavy ion escape are mainly attributed to substantial reductions in solar wind dynamic pressure and momentum density. This paper provides new insights into the dynamics of heavy ion escape under an exceptional state of the Mars–solar wind interaction.

Solar wind turbulence is a dynamical phenomenon that evolves with heliocentric distance. Orbiting Mars since 2014 September, Mars Atmosphere and Volatile EvolutioN offers a unique opportunity to explore some of its main properties beyond ∼1.38 au. Here, we analyze solar wind turbulence upstream of Mars' bow shock, utilizing more than 5 years of magnetic field and plasma measurements. This analysis is based on two complementary methodologies: (1) the computation of magnetohydrodynamic (MHD) invariants characterizing incompressible fluctuations; (2) the estimation of the incompressible energy cascade rate at MHD scales (i.e., 〈 ε ^T 〉 _MHD ). Our results show the solar wind incompressible fluctuations are primarily in a magnetically dominated regime, with the component traveling away from the Sun having a higher median pseudoenergy. Moreover, turbulent fluctuations have a total energy per mass of up to ∼ 300 km ^2 s ^−2 , a range smaller than reported at 1 au. For these conditions, we determine the probability distribution function of 〈 ε ^T 〉 _MHD ranges mainly between ∼ −1 × 10 ^−16 and ∼1 × 10 ^−16 J m ^−3 s ^−1 , with a median equal to −1.8 × 10 ^−18 J m ^−3 s ^−1 , suggesting back transfer of energy. Our results also suggest that ∣〈 ε ^T 〉 _MHD ∣ is correlated with the total energy per mass of fluctuations and that the median of 〈 ε ^T 〉 _MHD does not vary significantly with the cross-helicity. We find, however, that the medians of the inward and outward pseudoenergy cascade rates vary with the solar wind cross-helicity. Finally, we discuss these results and their implications for future studies that can provide further insight into the factors affecting the solar wind energy transfer rate.

During recent solar encounters, the Parker Solar Probe (PSP) began its initial dips below the Alfvén critical surface to measure in situ the sub-Alfvénic coronal wind. While the near-Sun super-Alfvénic solar wind is shown to be dominated by impulsive magnetic switchbacks (short magnetic field reversals), these brief encounters with the sub-Alfvénic coronal wind show switchbacks and associated magnetic holes (MHs) to still be present but different in character. In this work, we compare and contrast specific features of the switchbacks, including the change in B _r and V _r and associated boundary B -field dropouts (MHs) at locations when PSP was both above and below the Alfvén critical surface. We use observations from the PSP perihelion Encounters 8 (E8) and 12 (E12) in the analysis. We first perform a superposed epoch analysis to identify common features in the switchback boundaries, including the formation of the associated ∣ B ∣ dropouts/MHs in slow and fast flows. We then examine the presence of B -field dropouts/MHs as a function of Alfvén Mach number, M _A . From E12, we find that the switchbacks have a systematic reduction in rotation (and reduction in B _r deflection) with decreasing M _A . Further, the ∣ B ∣ dropouts/MHs associated with the boundaries were also found to decrease in strength and occurrence with M _A (with no or few ∣ B ∣ dropouts at M _A < 0.7). The results suggest that the switchback rotation and boundary-associated MHs are connected, possibly consistent with diamagnetic effects at the boundary that require large rotations to be initiated.