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

Global Hall MHD Simulations of the Solar Wind Implantation Flux on the Lunar Surface

The solar wind can directly interact with the lunar surface and provide an important source for surface space weathering and water generation. Here we study the solar wind implantation flux on the lunar surface with global Hall MHD simulations. The shielding effects of both the Earth’s magnetosphere and lunar magnetic anomalies are considered. It is found that a large-scale lunar mini-magnetosphere can be caused by the solar wind interaction with the magnetic anomalies on the lunar far side, which causes a large shielding area on the surface. In addition, the Earth’s magnetosphere brings a longitudinal variation in the implantation flux, with minimum fluxes at 0° longitude. With the integrated flux over a lunation, we find that there are some local cavities on the implantation flux map, which are colocated with both the magnetic anomalies and the lunar swirls. Further studies show that there is a south–north asymmetry in the implantation flux, which can be used to explain the lower water content observed in the southern hemisphere. Our results provide a global map of the solar wind implantation flux on the lunar surface and are useful for evaluating the large-scale effect of solar wind implantation and sputtering on the space weathering and the water or gas generation of the surface

Dependences of Energetic Neutral Atoms Energy on the Solar Wind Energy and Solar Zenith Angle Observed by the Chang’E-4 Rover

Solar wind can directly interact with the lunar surface and bring a space weathering effect. Some solar wind protons can be scattered as energetic neutral atoms (ENAs), which include rich information of the solar wind–surface interaction. However, people still know little about the ENA truth on the lunar ground due to the lack of in situ measurements. Different from the previous in-orbit measurements, here we present the first ground-based ENA measurements by the Chang’E-4 rover and find a good correlation between the mean ENA energy and the solar wind energy. Moreover, the loss rate of ENA energy can strongly depend on both the solar wind energy and the solar zenith angle (SZA), in which the energy loss rate can be enhanced by 73% when the solar wind energy increases from 400 to 1400 eV and can be reduced by 32% when the SZA increases from 57° to 71°. Combined with numerical simulations by SDTrimSP code, we propose that the solar wind protons can penetrate deeper into the lunar surface with a longer path length when the solar wind energy is higher or the SZA is lower, which results in a larger energy loss rate for the scattered ENAs. Our results provide an important constraint for the solar wind–surface research and have general implications in studying the surficial space weathering of the Moon and other airless bodies

M2 tumor-associated macrophage mediates the maintenance of stemness to promote cisplatin resistance by secreting TGF-β1 in esophageal squamous cell carcinoma

Abstract Background Esophageal squamous cell carcinoma (ESCC) is a deadly gastrointestinal malignancy, and chemotherapy resistance is a key factor leading to its poor prognosis. M2 tumor-associated macrophages (M2-TAMs) may be an important cause of chemoresistance in ESCC, but its exact mechanism is still unclear. Methods In order to study the role of M2-TAMs in ESCC chemoresistance, CCK-8, clone formation assay, flow cytometric apoptosis assay, qRT-PCR, western blotting, and serum-free sphere formation assays were used. In vivo animal experiments and human ESCC tissues were used to confirm the findings. Results In vitro and in vivo animal experiments, M2-TAMs reduced the sensitivity of ESCC cells to cisplatin. Mechanistically, M2-TAMs highly secreted TGF-β1 which activated the TGFβR1-smad2/3 pathway to promote and maintain the stemness characteristic of ESCC cells, which could inhibit the sensitivity to cisplatin. Using TGFβ signaling inhibitor SB431542 or knockdown of TGFβR1 could reverse the cisplatin resistance of ESCC cells. In 92 cases of human ESCC tissues, individuals with a high density of M2-TAMs had considerably higher levels of TGF-β1. These patients also had worse prognoses and richer stemness markers. Conclusion TGF-β1 secreted from M2-TAMs promoted and maintained the stemness characteristic to induce cisplatin resistance in ESCC by activating the TGFβ1-Smad2/3 pathway

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

Sensing an Intense Phytoplankton Bloom in the Western Taiwan Strait from Radiometric Measurements on a UAV

Rapid assessment of algal blooms in bays and estuaries has been difficult due to lack of timely shipboard measurements and lack of spatial resolution from current ocean color satellites. Airborne measurements may fill the gap, yet they are often hindered by the high cost and difficulty in deployment. Here we demonstrate the capacity of a low-cost, low-altitude unmanned aerial vehicle (UAV) in assessing an intense phytoplankton (Phaeocystis globosa) bloom (chlorophyll concentrations ranged from 7.3 to 45.6 mg/m3) in Weitou Bay in the western Taiwan Strait. The UAV was equipped with a hyperspectral sensor to measure the water color with a footprint of 5 m at every 30 m distance along the flight track. A novel approach was developed to obtain remote sensing reflectance (Rrs) from the UAV at-sensor radiometric measurements. Compared with concurrent and co-located field measured Rrs (14 stations in total), the UAV-derived Rrs showed reasonable agreement with root mean square difference ranging 0.0028–0.0043 sr− 1 (relative difference ~ 20–32%) of such turbid waters for the six MODIS bands (412–667 nm). The magnitude of the bloom was further evaluated from the UAV-derived Rrs. For the bloom waters, the estimated surface chlorophyll a concentration (Chl) ranged 6–98 mg/m3, which is 3–50 times of the Chl under normal conditions. This effort demonstrates for the first time a successful retrieval of both water color (i.e., Rrs) and Chl in a nearshore environment from UAV hyperspectral measurements, which advocates the use of UAVs for rapid assessment of water quality, especially for nearshore or difficult-to-reach waters, due to its flexibility, low cost, high spatial resolution, and sound accuracy