Analysis of the background signal in Tianwen-1 MINPA

Since November 2021, Tianwen-1 started its scientific instrument Mars Ion and Neutral Particle Analyzer (MINPA) to detect the particles in the Martian space. To evaluate the reliability of the plasma parameters from the MINPA measurements, in this study, we analyze and reduce the background signal (or noise) appearing in the MINPA data, and then calculate the plasma moments based on the noise-reduced data. It is found that the velocity from MINPA is highly correlated with that from the Solar Wind Ion Analyzer (SWIA) onboard the MAVEN spacecraft, indicating good reliability, and the temperature is also correlated with the SWIA data, although it is underestimated and has more scatter. However, due to the limited $2\pi$ field of view (FOV), it's impossible for MINPA to observe the ions in all directions, which makes the number density and the thermal pressure highly underestimated compared to the SWIA data. For these moments, a more complicated procedure that fully takes into account the limited FOV is required to obtain their reliable values. In addition, we perform a detailed analysis of the noise source and find that the noise comes from the electronic noise in the circuits of MINPA. Based on this study, we may conclude that MINPA is in normal operating condition and could provide reliable plasma parameters by taking some further procedures. The analysis of the noise source can also provide a reference for future instrument design.Comment: 15 pages, 11 figure

Proton pitch angle distributions in the Martian induced magnetosphere: A survey of Tianwen-1 Mars Ion and Neutral Particle Analyzer observations

The pitch angle distributions of ions and electrons can be affected by various processes; thus, they can serve as an important indicator of the physical mechanisms driving the dynamics of space plasmas. From observations from the Mars Ion and Neutral Particle Analyzer onboard the Tianwen-1 orbiter, we calculated the pitch angle distributions of protons in the Martian induced magnetosphere by using information from the magnetohydrodynamically simulated magnetic field, and we statistically analyzed the spatial occurrence pattern of different types of pitch angle distributions. Even though no symmetrical features were seen in the dataset, we found the dominance of the field-aligned distribution type over the energy range from 188 to 6232 eV. Maps of the occurrence rate showed the preferential presence of a trapped-like distribution at the lower altitudes of the surveyed nightside region. Although our results are more or less restricted by the adopted magnetic field, they indicate the complexity of the near-Mars proton pitch angle distributions and infer the possibility of wave–particle interactions in the Martian induced magnetosphere

Characterizing and Removing Ultra-Violet Contamination in Ion Observations on Board Tianwen-1

The Mars Ion and Neutral Particle Analyzer (MINPA) onboard Tianwen-1 aims to study the interaction between Mars and the solar wind via in situ ion measurement and energetic neutral atom imaging. Despite the efforts for Ultra-Violet suppression in MINPA design, 0.48% of ion observations from November 2021 to July 2022 were identified as UV-contaminated. The UV emissions primarily penetrate into the instrument through the ENA entrance. Statistically, the distribution of the UV contamination in phase space typically spans 3 to 4 azimuth sectors. The contamination is uniformly distributed across the polar dimension while, in the energy and mass dimensions, it is proportional to the time-of-flight duration. Comparisons between the in-flight performance and ground calibration suggest that azimuthal broadening and intensity variations of the contamination may result from differing responses across the azimuthal sectors. Based on the characteristics of the UV impact on MINPA ion observations, a removal algorithm is proposed to reduce contamination while preserving valid signals, which improves the data quality effectively and benefits the interpretation of MINPA’s ion measurements in the Martian space environment. The cause, effect, and distribution of the UV contamination obtained by this study may serve as a reference for other space ion observations

Inversion of Upstream Solar Wind Parameters from ENA Observations at Mars

An algorithm has been developed to invert the solar wind parameters from the hydrogen energetic neutral atom (H-ENA) measured in near-Mars space. Supposing the H-ENA is produced by change exchange collision between protons that originated in the solar wind and neutrals in the exosphere, an H-ENA model is established based on the magnetohydrodynamic (MHD) simulation of the solar wind interaction with Mars, to study the H-ENA characteristics. It is revealed that the solar wind H-ENAs are high-speed, low-temperature beams, just like the solar wind, while the magnetosheath H-ENAs are slower and hotter, with broader energy distribution. Assuming Maxwellian velocity distribution, the solar wind H-ENA flux is best fitted by a Gaussian function, from which the solar wind velocity, density, and temperature can be retrieved. Further investigation, based on the ENA flux simulated by the H-ENA model, reveals that the accuracy of inversed solar wind parameters is related to the angular and energy resolutions of the ENA detector. Finally, the algorithm is verified using the H-ENA observations from the Tianwen-1 mission. The upstream solar wind velocity when inversed is close to that of the in situ plasma measurement. Our result suggests the solar wind parameters inversed from H-ENA observation could be an important supplement to the dataset supporting studies on the Martian space environment, where long-term continuous monitoring of the upstream SW condition is lacking

Upstream Proton Cyclotron Waves at Mars During the Passage of ICMEs

International audienceThe presence of proton cyclotron waves (PCWs) upstream from Mars indicates picked up protons originating from the Martian extended hydrogen (H) exosphere by the solar wind and loss of H to interplanetary space. The occurrences and properties of PCWs associated with normal solar wind conditions have been extensively investigated since their initial detection about 32 years ago, but little attention has been paid to PCW activity under extreme space weather conditions. Here we characterize PCWs during the passage of interplanetary coronal mass ejections (ICMEs) through the Martian environment using the measurements by the Mars Atmosphere and Volatile EvolutioN spacecraft from December 2014 to February 2019. It is found that PCWs occur more frequently during perihelion periods (Ls = 180°-360°) than during aphelion periods (Ls = 0°-180°) for disturbed times of ICME passage. In the perihelion season, the PCW occurrence rate is increased on average by a factor of about 2 during the ICME phase relative to the pre-ICME and post-ICME phases. Moreover, PCWs reveal more pronounced wave characteristics with larger amplitudes, higher ellipticity, and smaller propagation angle with respect to the ambient magnetic field direction during the ICME phase

Mars Ion and Neutral Particle Analyzer (MINPA) for Chinese Mars Exploration Mission (Tianwen-1): Design and ground calibration

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 MINP

AME : A Cross-Scale Constellation of CubeSats to Explore Magnetic Reconnection in the Solar-Terrestrial Relation

A major subset of solar-terrestrial relations, responsible, in particular, for the driver of space weather phenomena, is the interaction between the Earth's magnetosphere and the solar wind. As one of the most important modes of the solar-wind-magnetosphere interaction, magnetic reconnection regulates the energy transport and energy release in the solar-terrestrial relation. In situ measurements in the near-Earth space are crucial for understanding magnetic reconnection. Past and existing spacecraft constellation missions mainly focus on the measurement of reconnection on plasma kinetic-scales. Resolving the macro-scale and cross-scale aspects of magnetic reconnection is necessary for accurate assessment and predictions of its role in the context of space weather. Here, we propose the AME (self-Adaptive Magnetic reconnection Explorer) mission consisting of a cross-scale constellation of 12+ CubeSats and one mother satellite. Each CubeSat is equipped with instruments to measure magnetic fields and thermal plasma particles. With multiple CubeSats, the AME constellation is intended to make simultaneous measurements at multiple scales, capable of exploring cross-scale plasma processes ranging from kinetic scale to macro scale

Tianwen-1 MINPA observations in the solar wind

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

AME: A Cross-Scale Constellation of CubeSats to Explore Magnetic Reconnection in the Solar–Terrestrial Relation

A major subset of solar–terrestrial relations, responsible, in particular, for the driver of space weather phenomena, is the interaction between the Earth's magnetosphere and the solar wind. As one of the most important modes of the solar–wind–magnetosphere interaction, magnetic reconnection regulates the energy transport and energy release in the solar–terrestrial relation. In situ measurements in the near-Earth space are crucial for understanding magnetic reconnection. Past and existing spacecraft constellation missions mainly focus on the measurement of reconnection on plasma kinetic-scales. Resolving the macro-scale and cross-scale aspects of magnetic reconnection is necessary for accurate assessment and predictions of its role in the context of space weather. Here, we propose the AME (self-Adaptive Magnetic reconnection Explorer) mission consisting of a cross-scale constellation of 12+ CubeSats and one mother satellite. Each CubeSat is equipped with instruments to measure magnetic fields and thermal plasma particles. With multiple CubeSats, the AME constellation is intended to make simultaneous measurements at multiple scales, capable of exploring cross-scale plasma processes ranging from kinetic scale to macro scale