The Mars Ion and Neutral Particle Analyzer (MINPA) is one of the three scientific instruments onboard the Tianwen-1 orbiter to investigate the Martian space environment. During Tianwen-1’s transfer orbit to Mars, the MINPA was switched on to measure the solar wind ions. Here, we present the first results of the MINPA observations in the solar wind. During cruise, nearly half of the MINPA ion field-of-view (FOV) was blocked by the lander capsule; thus only the solar-wind ions with azimuthal speeds pointing towards the unblocked FOV sectors could be detected. We perform a detailed comparison of the MINPA’s solar wind observations with data from Earth-based missions when MINPA reached its count-rate peak, finding a general consistency of the ion moments between them. The blocking effect due to the lander is evaluated quantitatively under varying solar-wind velocity conditions. Despite the blocking effect, the MINPA’s solar wind measurements during the transfer orbit suggest a good performance.
The main objective of the Mars Ion and Neutral Particle Analyzer (MINPA) aboard the Chinese Mars Exploration Mission (Tianwen-1) is to study the solar wind–Mars interaction by measuring the ions and energetic neutral atoms (ENAs) near Mars. The MINPA integrates ion and ENA measurements into one sensor head, sharing the same electronics box. The MINPA utilizes a standard toroidal top-hat electrostatic analyzer (ESA) followed by a time of flight (TOF) unit to provide measurement of ions with energies from 2.8 eV to 25.9 keV and ENAs from 50 eV to 3 keV with a base time resolution of 4 seconds. Highly polished silicon single crystal substrates with an Al2O3 film coating are used to ionize the ENAs into positive ions. These ions can then be analyzed by the ESA and TOF, to determine the energy and masses of the ENAs. The MINPA provides a 360°×90° field of view (FOV) with 22.5°×5.4° angular resolution for ion measurement, and a 360°×9.7° FOV with 22.5°×9.7° angular resolution for ENA measurement. The TOF unit combines a –15 kV acceleration high voltage with ultra-thin carbon foils to resolve H+, He2+, He+, O+, O2+ and CO2+ for ion measurement and to resolve H and O (≥ 16 amu group) for ENA measurement. Here we present the design principle and describe our ground calibration of the MINPA.
Kinetic-scale magnetic holes (KSMHs) are structures characterized by a significant magnetic depression with a length scale on the order of the proton gyroradius. These structures have been investigated in recent studies in near-Earth space, and found to be closely related to energy conversion and particle acceleration, wave-particle interactions, magnetic reconnection, and turbulence at the kinetic-scale. However, there are still several major issues of the KSMHs that need further study — including (a) the source of these structures (locally generated in near-Earth space, or carried by the solar wind), (b) the environmental conditions leading to their generation, and (c) their spatio-temporal characteristics. In this study, KSMHs in near-Earth space are investigated statistically using data from the Magnetospheric Multiscale mission. Approximately 200,000 events were observed from September 2015 to March 2020. Occurrence rates of such structures in the solar wind, magnetosheath, and magnetotail were obtained. We find that KSMHs occur in the magnetosheath at rates far above their occurrence in the solar wind. This indicates that most of the structures are generated locally in the magnetosheath, rather than advected with the solar wind. Moreover, KSMHs occur in the downstream region of the quasi-parallel shock at rates significantly higher than in the downstream region of the quasi-perpendicular shock, indicating a relationship with the turbulent plasma environment. Close to the magnetopause, we find that the depths of KSMHs decrease as their temporal-scale increases. We also find that the spatial-scales of the KSMHs near the subsolar magnetosheath are smaller than those in the flanks. Furthermore, their global distribution shows a significant dawn-dusk asymmetry (duskside dominating) in the magnetotail.
We present preliminary results of a new global Magnetohydrodynamics (MHD) simulation model of the Jovian magnetosphere. The model incorporates mass loading from Jupiter's satellite Io, the planet's fast corotation, and electrostatic coupling between its magnetosphere and ionosphere (M-I coupling). The basic configuration of the Jovian magnetosphere including the equatorial plasma flow pattern, the corotation enforcement current system, and the field aligned currents (FACs) in the ionosphere are presented under an antiparallel interplanetary magnetic field (IMF) condition. The simulation model results for equatorial density and pressure profiles are consistent with results from data-based empirical models. It is also found that there are similarities between the FACs distribution in the ionosphere and the observed aurora features, showing the potential application of the simple ionospheric model to the complicated M-I coupling. This model will help deepen our understanding of the global dynamics of the Jovian magnetosphere.