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Objectives: The stability of ultra-stable oscillator (USO) which provides frequency standard and transmits downlink signal affects the accuracy of one-way Doppler measurements directly. It is a necessity to estimate the frequency bias during orbit determination with one-way Doppler measurements. Methods: First, the one-way Doppler observation model and observation partial derivative are deduced theoretically, and the main error sources affecting the accuracy are analyzed. Then, the frequency deviation is estimated and the USO long-term drift prediction model is constructed during the execution of Tianwen-1 precise orbit determination using the one-way Doppler measurements. Finally, the accuracy of frequency bias resolution is analyzed theoretically based on its key factors. Results: The USO drift rate is 0.075 75±0.006 20 Hz/d. Conclusions: This paper provides a feasible frequency drift calibration method for space-borne USO, and it constructs a priori frequency model for space-borne USO of Tianwen-1. [ABSTRACT FROM AUTHOR]

Abstract The Chinese Mars rover Zhurong successfully landed in southern Utopia Planitia on Mars in May 2021. Previous research suggested a Hesperian ocean may have existed in the northern lowland on Mars. Recent research observed water-related features at the Zhurong landing site from in situ data. In this study, we conducted a comprehensive geomorphological analysis of the landing area using remote sensing data, supplemented by in situ observations, and unveiled features consistent with the existence of a nearshore zone in southern Utopia. Different types of water-related geomorphological features were separated by specific topographic contours, suggesting different types of marine environments. The area was subdivided into a foreshore highland-lowland transition unit, a shallow marine unit and a deep marine unit. In situ observations including sedimentary deposit rocks, water-related lamination features, and subsurface sedimentary layers, also indicate past water activities. Results suggested an evolution scenario of the nearshore zone in southern Utopia: (1) Flooding of the Utopia Planitia in Late Noachian around 3.65–3.68 Ga reached the foreshore unit; (2) formation of the shallow and deep marine units after the flooding was completed by about 3.5 Ga and 3.42 Ga in Early Hesperian, respectively; (3) gradual loss of subsurface volatiles during the Amazonian epoch.

Internal gravity waves (IGWs) are critical in driving Martian atmospheric motion and phenomena. This study investigates Martian IGWs by using high-resolution data from China’s Tianwen-1 mission and the National Aeronautics and Space Administration’s Mars Global Surveyor (MGS) by the radio occultation (RO) technique. Key IGW parameters, such as vertical and horizontal wavelengths, intrinsic frequency, and energy density, are extracted based on vertical temperature profiles from the Martian surface to ~50 km altitude. Data reveal that the Martian IGWs are predominantly small-scale waves, with vertical wavelengths between 6 and 13 km and horizontal wavelengths extending to thousands of kilometers. These waves propagate almost vertically and exhibit low intrinsic frequencies close to the inertial frequency, with the characteristic of low-frequency inertial IGWs. Tianwen-1 data indicate stronger IGW activity, higher energy density, and less dissipation than MGS data in the northern hemisphere. Moreover, MGS data in the southern hemisphere show higher buoyancy frequencies and lower vertical wavelengths, suggesting more stable atmospheric conditions conducive to IGW propagation. These extracted IGW characteristics can enhance our understanding of the atmospheric dynamics on Mars and contribute valuable information for parameterization in global circulation models.

After landing in the Utopia Planitia, Tianwen-1 formed the deepest landing crater on Mars, approximately 40 cm deep, exposing precious information about the mechanical properties of Martian soil. We established numerical models for the plume-surface interaction (PSI) and the crater formation based on Computational Fluid Dynamics (CFD) methods and the erosion model modified from Roberts’ Theory. Comparative studies of cases were conducted with different nozzle heights and soil mechanical properties. The increase in cohesion and internal friction angle leads to a decrease in erosion rate and maximum crater depth, with the cohesion having a greater impact. The influence of the nozzle height is not clear, as it interacts with the position of the Shock Diamond to jointly control the erosion process. Furthermore, we categorized the evolution of landing craters into the dispersive and the concentrated erosion modes based on the morphological characteristics. Finally, we estimated the upper limits of the Martian soil’s mechanical properties near Tianwen-1 landing site, with the cohesion ranging from 2612 to 2042 Pa and internal friction angle from 25° to 41°.

Since November 2021, the Tianwen-1 mission has activated its scientific instrument, the Mars Ion and Neutral Particle Analyzer (MINPA), to detect particles within 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. Remarkably, our findings reveal a strong correlation between the velocity measurements from MINPA and those from the Solar Wind Ion Analyzer (SWIA) onboard the MAVEN spacecraft, underscoring MINPA's accuracy. Similarly, temperature measurements correlate with SWIA data, albeit with a tendency towards underestimation and greater variability. A significant limitation, however, is MINPA's 2 π field of view (FOV), which restricts its ability to observe ions omnidirectionally, leading to a substantial underestimation of number density and thermal pressure compared to SWIA measurements. Addressing this challenge necessitates a sophisticated approach that fully accommodates the FOV constraints to derive accurate values for these parameters. Moreover, our comprehensive investigation into the noise origins traced it back to electronic noise within MINPA's circuitry. This study confirms MINPA's operational efficacy and potential to yield dependable plasma parameters with further procedures and contributes valuable insights for the design of future scientific instruments. [ABSTRACT FROM AUTHOR]

The Chinese Mars rover Zhurong successfully landed in southern Utopia Planitia on Mars in May 2021. Previous research suggested a Hesperian ocean may have existed in the northern lowland on Mars. Recent research observed water-related features at the Zhurong landing site from in situ data. In this study, we conducted a comprehensive geomorphological analysis of the landing area using remote sensing data, supplemented by in situ observations, and unveiled features consistent with the existence of a nearshore zone in southern Utopia. Different types of water-related geomorphological features were separated by specific topographic contours, suggesting different types of marine environments. The area was subdivided into a foreshore highland-lowland transition unit, a shallow marine unit and a deep marine unit. In situ observations including sedimentary deposit rocks, water-related lamination features, and subsurface sedimentary layers, also indicate past water activities. Results suggested an evolution scenario of the nearshore zone in southern Utopia: (1) Flooding of the Utopia Planitia in Late Noachian around 3.65–3.68 Ga reached the foreshore unit; (2) formation of the shallow and deep marine units after the flooding was completed by about 3.5 Ga and 3.42 Ga in Early Hesperian, respectively; (3) gradual loss of subsurface volatiles during the Amazonian epoch. [ABSTRACT FROM AUTHOR]

The Martian bow shock has been extensively studied through magnetic field and plasma instrument observations from various Mars space missions. However, prior investigations primarily involve statistical analyses based on single spacecraft crossings, leaving the asymmetry of the Martian bow shock unstudied through simultaneous two‐spacecraft observations. In this study, utilizing simultaneous observations from Tianwen‐1 and MAVEN, we examine the instantaneous asymmetry of the Martian bow shock. We present the asymmetry of the Martian bow shock in the Mars‐Solar‐Electric and Mars‐Solar‐Orbital reference frames, possibly influenced by the solar wind motional electric field and Martian crustal magnetic field, respectively. Moreover, we suggest that the bow shock exhibits increased asymmetry under stronger solar wind motional electric field conditions. This study highlights how a two‐point observation approach offers valuable insights into the dynamic behavior of the Martian induced magnetosphere. Plain Language Summary: Scientists have been studying the Martian bow shock, which slows down the solar wind from supersonic to subsonic, using instruments on different Mars missions. But most studies only use data from one spacecraft, so we don't know much about how the bow shock varies in different places at the same time. In this study, we looked at data from two spacecraft, Tianwen‐1 and MAVEN, at the same time to see if we could find any differences. We found that the bow shock is different in the northern and southern parts of Mars in different reference frames, and this might be because of the solar wind electric field and the Martian crustal field. We also noticed that the bow shock is more different when the solar wind electric field is stronger. Such two‐spacecraft observations helps us understand more about how the magnetic environment around Mars works. Key Points: We investigated the asymmetry of Martian bow shock utilizing two‐spacecraft observations at distinct locationsThe dayside Martian crustal field may induce the north‐south asymmetry of the bow shockThe solar wind electric field may cause bow shock asymmetry in the Mars‐Solar‐Electric frame, with stronger fields increasing the effect [ABSTRACT FROM AUTHOR]

Crater detection is useful for research into dating a planetary surface's age and geological mapping. The high-resolution imaging camera (HiRIC) carried by the Tianwen-1 rover provides digital image model (DIM) datasets with a resolution of 0.7 m/pixel, which are suitable for detecting meter-scale craters. The existing deep-learning-based automatic crater detection algorithms require a large number of crater annotation datasets for training. However, there is currently a lack of datasets of optical images of small-sized craters. In this study, we propose a model based on the Segment Anything Model (SAM) to detect craters in Tianwen-1's landing area and perform statistical analysis. The SAM network was used to obtain a segmentation mask of the craters from the DIM images. Then non-circular filtering was used to filter out irregular craters. Finally, deduplication and removal of false positives were performed to obtain accurate circular craters, and their center's position and diameter were obtained through circular fitting analysis. We extracted 841,727 craters in total, with diameters ranging from 1.57 m to 7910.47 m. These data are useful for further Martian crater catalogs and crater datasets. Additionally, the crater size–frequency distribution (CSFD) was also analyzed, indicating that the surface ages of the Tianwen-1 landing area are ~3.25 billion years, with subsequent surface resurfacing events occurring ~1.67 billion years ago. [ABSTRACT FROM AUTHOR]

Transverse aeolian ridges (TARs) are enigmatic landforms found across Mars, whose formation mechanism remains largely unknown. China's Tianwen-1 mission, which landed on Mars in 2021, provided extensive data aiding in-depth investigations of TARs. However, manually identifying TARs across large regions of Mars is time-consuming and labor-intensive, making it impossible to complete the entire region's TAR identification. To solve this issue, we propose the AiTARs-Net, an automatic arbitrary-oriented TRA detection network. This model begins by extracting TAR features using an enhanced dimension-aware global-local attention module, which focuses on interactions between spatial and channel features to capture discriminative features of TARs. After that, we employ an anchor-free proposal generation network to produce TAR candidates with arbitrary orientations. The proposal generation network uses a nonaxis-aligned two-variable Gaussian function to model the target as an oriented center heatmap. Then, the oriented bounding box and category information are predicted at the corresponding center position. Finally, we introduce the rotated region-based convolutional neural network to refine the proposals to obtain more accurate TARs' locations and orientations. To assess the efficacy of our proposed method, we built the Martian TARs dataset (M-TARset), an compilation of TARs labeled in six different topographical and morphological types, containing various shapes and illumination scales, to facilitate training and prediction of potential TARs. The experimental results obtained on a Martian TARs dataset and a large-scale TARs extraction at the Zhurong landing site confirm that the proposed framework outperforms the leading generic object extraction methods in accuracy, demonstrating its strong generalization abilities for large-scale TAR detection. The source code and M-TARset are available at https://github.com/PlanetaryScience3510/M-TARset. [Display omitted] • We proposed a novel AiTARs-Net framework for large-scale TARs automatic extraction. • We proposed enhanced global-local feature extraction module for capture TAR features. • We introduced anchor-free network for generating TAR proposal. • We created a Martian TARs dataset to train and test TAR detection model. [ABSTRACT FROM AUTHOR]

This study delves into a Pick‐Up Ion (PUI) event captured by the Mars Ion and Neutral Particle Analyzer aboard Tianwen‐1, revealing a faster acceleration than expected within the Martian magnetosheath. This event suggests the presence of a convection electric field considerably stronger than that typically observed in the solar wind. Through Magnetohydrodynamic simulation, we identified two regions of intensified convection electric fields within the inner magnetosheath, prominently manifested at mid to high solar zenith angles (SZA = 40°–70°) in the X‐Z plane of the Mars Solar Electric field coordinates. Tianwen‐1 observed that the peak of the electric field strength, up to five times of that in the solar wind, is located at the upper edge or within the Magnetic Pileup Boundary. Further study by test particle simulations showed acceleration by the electric field effectively doubles the energy gain of PUIs, in comparison to scenarios absent of this extra acceleration. It is revealed that the presence of such electric field regions within the Martian magnetosheath is a prevailing feature, shaped by the solar wind's interaction with Mars and modulated by the planet's rotating crustal magnetic fields. Plain Language Summary: The interaction between planets and their upstream solar wind holds great significance for the long‐time climate evolution of planets. Mars lacks a global dipole magnetic field, which makes it easier for these planetary ions to escape through acceleration by the solar wind convection electric field. The observations of Tianwen‐1 and Mars Atmosphere and Volatile Evolution satellites provide a great opportunity to study the acceleration of planetary ions by this electric field. Through a case study involving observation and simulation, we confirm that there are two regions in the Martian magnetosheath, where the convection electric field is stronger than in the solar wind. This electric field may rapidly energize the ions and possibly result in intensified ion escape. Key Points: In the Martian magnetosheath, joint effects of the plasma flow around Mars and the interplanetary magnetic field pileup result in enhanced convection electric fieldThe strong E field envelops a large part of the Magnetic Pileup Boundary (MPB), with the maximum at the med‐high solar zenith angles, at the upper edge or within the MPBThe crustal magnetic fields modulate the distribution of the strong E field, leading to hemispheric asymmetry [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The radio occultation method, one of the methods used to provide planetary atmospheric profiles with high vertical resolution, was applied to China's first Mars mission, Tianwen-1. We carried out observations based on the Chinese Deep Space Network, and one-way, two-way, and three-way modes were used for Doppler observations from the Tianwen-1 spacecraft. We successfully obtained effective observations from Tianwen-1 on 22 and 25 March 2022. An inversion system developed for Tianwen-1 radio occultation observations enabled the derivation of neutral atmospheric density, pressure, temperature, and electron density profiles of Mars. Utilizing one-way tracking data, Martian ionospheric electron density profiles were retrieved at latitudes between 68.7 and 70.7 degrees (N). However, the presence of strong random walk noise in one-way tracking data led to poor inversion results. Meanwhile, Martian ionospheric electron density and neutral atmosphere profiles were extracted from two-way and three-way tracking data at latitudes between 55.1 and 57.0 degrees (S) on 22 March and at latitudes between 62.8 and 63.4 degrees (S) on 25 March. Importantly, our inversion results from Tianwen-1 maintained consistency with results from the Mars Express and the Chapman theory (mainly in the M2 layer). Through two days' observation experiments, we established and verified the occultation solution system and prepared for the follow-up occultation plans. [ABSTRACT FROM AUTHOR]

Pitted cones are cone-shaped structures, spanning from meters to kilometers in size, characterized by summit depressions. They are widely distributed on the surface of Mars with various origins, such as rootless cones, mud volcanoes, cinder or scoria cones, tuff rings or cones, pingos, and dirt cones. If the pitted cones identified in southern Utopia Planitia are mud volcanoes, as is speculated, they could be of particular interest due to the fact that mud volcanoes on Earth bring sediments from a depth of meters to kilometers to the surface. In this study, we have investigated the pitted cones near Zhurong rover's landing site in southern Utopia Planitia, utilizing recent images and digital elevation models obtained from the High Resolution Imaging Camera instrument onboard China's Tianwen-1 orbiter. By leveraging the high-resolution images and digital elevation models, we have conducted a geometric measurement to distinguish the origin of pitted cones in the vicinity of the Zhurong rover. The morphological characteristics of these pitted cones indicate an explosive mud volcano origin. These explosive mud volcanoes could have formed by the violent eruption of subsurface overpressurized sediments generated from the combined effect of overburden pressure and anomalous high heat flow. The sediments forming the pitted cones in the northern plains could be the remnants of an ancient ocean. With future in-situ observations of these pitted cones, we hope to gain further insights into the sediments of the putative northern ocean, as well as the physical and chemical properties of the Martian subsurface during the formation of the pitted cones. [ABSTRACT FROM AUTHOR]

Decades of research using remotely sensed data have extracted evidence for the presence of an ocean in the northern lowlands of Mars in the Hesperian (∼3.3 Ga), but these claims have remained controversial due to the lack of in situ analysis of the associated geologic unit, the Vastitas Borealis Formation (VBF). The Tianwen-1/Zhurong rover was targeted to land within the VBF near its southern margin and has traversed almost 2 km southward toward the interpreted shoreline. We report here on the first in situ analysis of the VBF that reveals sedimentary structures and features in surface rocks that suggest that the VBF was deposited in a marine environment, providing direct support for the existence of an ancient (Hesperian) ocean on Mars. [ABSTRACT FROM AUTHOR]

China’s first Mars exploration mission, Tianwen-1, successfully landed in southern Utopia Planitia on Mars on May 15, 2021. This work presents a detailed investigation of the geologic context of the landing area surface for this mission based on orbital remote-sensing data. We constructed a geomorphologic map for the Tianwen-1 landing area. Results of our detailed geomorphologic map show several major landforms within the landing area, including rampart craters, mesas, troughs, cones, and ridges. Analysis of materials on the landing area surface indicates that most of the landing area is covered by Martian dust. Transverse aeolian ridges are widely distributed within the landing area, indicating the surface contexts were (and still are) modified by regional winds. In addition, a crater counting analysis indicates the landing area has an absolute model age of ~3.3 Ga and that a later resurfacing event occurred at ~1.6 Ga. Finally, we outline four formational scenarios to test the formation mechanisms for the geomorphologic features on the landing area surface. The most likely interpretation to explain the existence of the observed surface features can be summarized as follows: A thermal influence may have played an important role in the formation of the surface geomorphologic features; thus, igneous-related processes may have occurred in the landing area. Water ice may also have been involved in the construction of the primordial surface configuration. Subsequent resurfacing events and aeolian processes buried and modified the primordial surface.

The plume–surface interaction (PSI) is a common phenomenon that describes the environment surrounding the landers resulting from the impingement of hot rocket exhaust on the regolith of planetary bodies. The PSI will cause obscuration, erosion of the planetary surface, and high-speed spreading of dust or high-energy ejecta streams, which will induce risks to a safe landing and cause damage to payloads on the landers or to nearby assets. Safe landings and the subsequent scientific goals of deep-space exploration in China call for a comprehensive understanding of the PSI process, including the plume flow mechanics, erosion mechanism, and ejecta dynamics. In addition, the landing crater caused by the plume provides a unique and insightful perspective on the understanding of PSI. In particular, the PSI can be used directly to constrain the composition, structure, and mechanical properties of the surface and subsurface soil. In this study, we conducted a systematic review of the phenomenology and terrestrial tests of PSI: we analyzed the critical factors in the PSI process and compared the differences in PSI phenomena between lunar and Martian conditions; we also reviewed the main erosion mechanisms and the evolution and development of terrestrial tests on PSI. We discuss the problems with PSI, challenges of terrestrial tests, and prospects of PSI, and we show the preliminary results obtained from the landing crater caused by the PSI of Tianwen-1. From analysis of the camera images and digital elevation model reconstructions, we concluded that the landing of Tianwen-1 caused the deepest crater (depth > 40 cm) on a planetary surface reported to date and revealed stratigraphic layers in the subsurface of Martian soil. We further constrained the lower bounds of the mechanical properties of Martian soil by a slope stability analysis of the Tianwen-1 landing crater. The PSI may offer promising opportunities to obtain greater insights into planetary science, including the subsurface structure, mineral composition, and properties of soil.

Ground calibration experiments of the Mars orbiter magnetometer (MOMAG) onboard the orbiter of Tianwen-1 were performed to determine the sensitivity, misalignment angle, and offset of the sensors. The linearity of the applied calibrated magnetic fields and the output from the sensors were confirmed to be better than 10−4, and the sensor axes were orthogonal to each other within 0.5 degrees. The temperature dependencies of the sensitivity and misalignment angle were examined, but no clear signatures of temperature dependencies could be seen. Sensor offset and the stability of sensor offset drift with a temperature change were also determined by the rotation method. The stability of the sensor offset drift was less than 0.01 nT/°C. The ground calibration of MOMAG determines all the calibration parameters of the sensors for accurate magnetic field measurements in orbit with the appropriate corrections.

The Mars Surface Composition Detector (MarSCoDe) is a remote sensing instrument mounted on the front deck of the Zhurong rover in China's Tianwen-1 mission. The MarSCoDe adopts Laser-Induced Breakdown Spectroscopy (LIBS), along with Short Wave Infrared Spectroscopy (SWIR) and a telescopic micro-imager, to perform in situ detection of the chemical composition of soils, rocks, and minerals on the Martian surface. Since the MarSCoDe LIBS system works in extraterrestrial environments, it is important to equip the system with a set of onboard calibration targets, which are used for assessing the real-time performance of the instrument under various environmental conditions and conducting instrumental response calibration. Twelve dedicated LIBS reference samples were embedded as the MarSCoDe calibration target (MCCT) set, which plays a critical role in LIBS calibration before conducting LIBS analysis. This paper elaborates on the selection, development, characterization and testing of the MCCT set. The underlying scientific reasons and technical requirements that determine the selection of MCCT samples are introduced. The development procedures and mechanical performance test of both the calibration samples and the assembly holder are presented. Then, a comparison of the MCCTs and the characterization and scientific testing are described. The LIBS spectra of the MCCTs collected in three different atmospheric scenarios, namely laboratory-simulated Martian, normal terrestrial, and in situ Martian atmosphere, were investigated. The laboratory results and in situ behaviour show that the MarSCoDe instrument and the MCCT set can soundly adapt to the Martian environment with sufficient performance, as indicated by the fact that the spectral lines of the main elements in the calibration targets can be well identified and distinguished, including Ti, Si, Al, Fe, Mg, P, Ca, Na, K, O, C, H, S, etc. The MCCT samples provide a good reference for analysing Martian surface material composition and formulating the transfer relationship between the LIBS spectra measured in different atmospheric environments. [ABSTRACT FROM AUTHOR]

China's first Mars probe, the Tianwen-1, successfully landed on the Martian Utopia Plain on May 15, 2021. The multi-functional obstacle avoidance sensor (MOAS) has been the key navigation equipment for the entry, descent, and landing (EDL) operation of Tianwen-1. The MOAS integrates a landing camera and a laser imaging module and can acquire sequential optical images of the landing process of Tianwen-1 and high-resolution topography of the Martian surface. As a navigation sensor, the MOAS plays a key role in the processes of back cover avoidance, coarse obstacle avoidance, and hovering fine obstacle avoidance from the height of 10 km to landing. The MOAS's laser imaging module uses a new-generation scanning component, a two-dimensional MEMS scanning mirror, which is a unique feature compared to other space lidars. In this paper, optical and electronic designs of the MOAS are analyzed in detail. Based on the open-loop control feature of a MEMS scanning mirror, an online training and calibration method is proposed to increase the accuracy of optical angle control to 0.02°. In addition, the ground performance validation and the space environment testing of MOAS are described in detail. The inflight performance of MOAS is evaluated based on the sequential camera images and 3D point cloud data. In addition, the MOAS combines the attributes of a scientific instrument. The images obtained by the sensor can reconstruct the descending trajectory of Tianwen-1, determine accurate landing coordinates, and acquire information on the topography, surface reflectivity, and sand and dust of Mars. [ABSTRACT FROM AUTHOR]

Mars orbiter magnetometer (MOMAG) is one of seven science payloads onboard Tianwen-1's orbiter. Unlike most of the satellites, Tianwen-1's orbiter is not magnetically cleaned, and the boom where placed the magnetometer's sensors is not long enough. These pose many challenges to the magnetic field data processing. In this study, we introduce the in-flight calibration process of the Tianwen-1/MOMAG. The magnetic interference including spacecraft generated dynamic field and the slowly-changing zero offsets are cleaned in sequence. Then the calibrated magnetic field data are compared with the data from the Mars atmosphere and volatile EvolutioN (MAVEN). We find that some physical structures in the solar wind are consistent between the two data sets, and the distributions of the magnetic field strength in the solar wind are very similar. These results suggest that the in-flight calibration of the MOMAG is successful and the MOMAG provides reliable data for scientific research. [ABSTRACT FROM AUTHOR]

As one of the prominent landforms in the Zhurong landing region, mesas are geological features with flat tops and steep marginal cliffs. The mesas are widely distributed along the dichotomy boundary. There are various interpreted origins proposed for the mesas, such as the erosion of sedimentary layers, tuyas eruptions, or surface collapse due to the catastrophic release of groundwater. We investigate the detailed morphological characteristics of the mesas on the Late Hesperian Lowland unit within the Utopia Planitia. We observe morphological evidence for both the ice-bearing interior mesas and the sedimentary origin, including (1) small pits on the crater wall and mesa cliff formed by the release of volatiles like ice; (2) lobate flows at the base of mesas formed by the melting of subsurface ice; (3) layered mesas indicating sedimentary origin; (4) grooves on the top surface of mesas formed by the volumetric compaction of sedimentary deposits. The results indicate that the mesas in the study area are formed by the erosion of sedimentary layers and representative of the Noachian oceanic sediments. We propose an evolutionary model for the mesas. This study will provide some insights into future research of ancient ocean hypothesis of Mars and interesting targets for the exploration of the Zhurong rover. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Martian regolith is one of the primary science objectives of Mars exploration missions. The Rover Penetrating Radar carried by Zhurong rover allows for high-resolution subsurface imaging and in-situ measurements of Martian regolith dielectric properties, which are crucial to advance our understanding of Martian geology and hydrological evolution. While earlier studies have derived dielectric constants for the shallow subsurface, further characterization of subsurface materials requires the determination of attenuation properties. In this study, we applied the centroid-frequency shift method to explore the attenuation property of the Martian regolith in the frequency domain. Lateral attenuation variation was analyzed in detail by integrating subsurface radargram and navigation terrain images. The results show that, within a depth of ∼4 m, the attenuation of radar signal for Zhurong subsurface material is equal to a loss tangent of 0.0079, with a standard deviation of 0.001. Based on the loss tangent value, dielectric permittivity and ground characterization, we preclude the possibility that the regolith is predominantly igneous materials. The lateral variation of the attenuation property could likely be attributed to changes in the proportion of duricrusts, which are heterogeneously distributed along the rover traverse. Our findings offer valuable information for understanding the Martian regolith and its evolution, serving as a important reference for future Mars sample return missions. • We used the centroid-frequency shift method to estimate the loss tangent of Martian regolith. • We compared the estimated results using CFS method and time-domain based method. • The regolith's origin was analyzed based on dielectric properties and ground characterization. • The heterogeneity of regolith was attributed to the distribution of subsurface rocks. [ABSTRACT FROM AUTHOR]

The morphology and surface characteristics of Transverse Aeolian Ridges (TARs) reflect the recent and current environmental evolution of Mars. This study investigates the influence of typical Martian non-aeolian landforms impacted on the distribution and morphology of TARs using multi-source high-resolution orbiter images in the Zhurong rover's landing region at the south of Utopian Plain. This study proposes an automatic and effective approach for extracting TARs, while classifying their types and estimating their geometric parameters, including length, width, height, and angle. The obtained results confirm the effectiveness of the proposed method. In the Zhurong rover's landing region, TARs in flat areas have a sparse distribution and simple morphology. However, TARs are more concentrated and diverse in morphology around typical non-aeolian landforms such as cones and troughs. The orientation of TARs is determined by wind direction, and their width is affected by sediment richness. The morphology and distribution of TARs are also influenced by typical non-aeolian landforms, which modify local wind fields and sediments. • An automatic extraction process is developed to extract the characteristics of TARs and to classify their types. • The impact of non-aeolian landforms on the distribution and morphology of TARs is discussed. • Non-aeolian landforms can increase the geometric parameter range of TARs up to twice in the HiRISE coverage area. [ABSTRACT FROM AUTHOR]

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The Rover-mounted Subsurface Penetrating Radar (RoSPR) is one of the scientific payloads onboard China's first independent Mars exploration mission, Tianwen-1. The radar aims to characterize the thickness of the upper Martian soil and investigate the subsurface stratigraphy by collecting and processing the data. This article is mainly divided into two parts, the introduction of data pre-processing and analysis of pre-processed radar signals, aiming at helping scientists make more effective use of radar data. The first part describes the operating principle of the RoSPR and the procedure of radar data pre-processing at all levels. Data pre-processing is mainly designed to transfer the raw data format to a common PDS (Planetary Data System) and eliminate the influence of the instrument. In the signal analysis part, the performances of both self-check signals and echo signals of low- and high-frequency channels are analyzed, which indicate a stable radar system and are useful for background removal. Phase and time calibration is of great importance for improving data quality and making the radar data more accurate. Moreover, further processing is required to obtain clear radar images, such as filtering, background removal and gain setting. [ABSTRACT FROM AUTHOR]

Aiming at the problem of rover positioning in Chinese Mars exploration mission Tianwen-1, the related research and accuracy analysis have been carried out. Methods: According to the existing measurement and control system and considering that the rover has no ground ranging data, we proposed a method to locate the rover using same-beam very long baseline interferometry (SBI) data of the orbiter and rover. Since it is not possible to determine the ambiguity using SBI and ranging data while deter‐ mining the orbit and positioning the rover at the same time, the proposed method which only uses SBI data for the rover positioning under the fixed orbital situation is analyzed. Results: The results show that the rover positioning error decreases with the increase of orbital accuracy. If the orbital accuracy is increased from 1 km to 100 m or 10 m,the rover positioning error using 6-hour SBI data can be reduced to hundreds of meters. Conclusions: More data can further reduce the positioning error and the positioning accuracy can be improved obviously with an elevation constraint. [ABSTRACT FROM AUTHOR]

Objectives: Tianwen-1 is the first independent interplanetary mission of China, and it was launched on 23 July 2020 and delivered directly into the Earth-Mars transfer orbit, which arrived at Mars in February 2021. It will complete orbiting, landing, and roving tasks in one operation. Exploiting tracking da‐ ta from gathered during this science exploration and extended mission, this paper explores possible ways to improve the Mars gravity field model by simulation. Methods: We designed two types of orbits, including the polar orbits with near zero eccentricity and the near equatorial orbit with large eccentricity. Based on these two types of orbits, we recovered six gravity solutions considering various error sources, such as measurement noise, solar pressure error, rotation model error, and tracking time length. We used the power spectrum method to analyze and evaluate these recovered gravity models. Results: We find that a month of tracking data from the polar orbit or the combined polar and near equatorial orbit could be used to properly reconstruct the Mars gravity field model with orders and degrees of 42 under the 0.1 mm/s measurement noise. When 10% solar pressure error is added, the gravity model solution only suffers a slight influence showing in the power spectrum analysis. Furthermore, when Mars rotation model error is added, the degree variances of gravity models are affected only after the 35-order and degree. Conclusions: The results show that considering the influence of comprehensive error, the accuracy of gravity field solutions of the two types of orbits is similar. Nevertheless, the orbit with large eccentricity near the equator has a slightly stronger constraint on more than 35-order and degree coefficients. Besides, when the track tracking data collected from the near equatorial orbit phase are added in the recovering of Mars gravity model, the pro‐ posed model can improve the precise orbit determination accuracy of a spacecraft with near-equatorial orbit. [ABSTRACT FROM AUTHOR]

The Mars Surface Composition Detector (MarSCoDe) carried by the Zhurong rover of China's Tianwen-1 mission uses Laser-Induced Breakdown Spectroscopy (LIBS) to detect and analyze the material composition on Martian surfaces. As one extraterrestrial remote LIBS system, it is necessary to adopt effective and reliable preprocessing methods to correct the spectral drift caused by the changes in environmental conditions, to ensure the analysis accuracy of LIBS scientific data. This paper focuses on the initial spectral drift correction and estimates the accuracy of on-board wavelength calibration on the LIBS calibration target measured by the MarSCoDe LIBS. There may be two cases during the instrument launch and landing, as well as the long-term operation: (a) the initial wavelength calibration relationship can still apply to the on-board LIBS measurement; and (b) the initial wavelength calibration relationship has been changed, and a new on-board calibration is needed to establish the current relationship. An approach of matching based on global iterative registration (MGR) is presented in respect to case (a). It is also compared with the approach of particle swarm optimization (PSO) for case (b). Furthermore, their accuracy is estimated with the comparison to the National Institute of Standards and Technology (NIST) database. The experimental results show that the proposed approach can effectively correct the drift of the on-board LIBS spectrum. The the root-mean-square error (RMSE) of the internal accord accuracy for three channels is 0.292, 0.223 and 0.247 pixels, respectively, compared with the corrected Ti-alloy spectrum and the NIST database, and the RMSE of the external accord accuracy is 0.232, 0.316 and 0.229 pixels, respectively, for other samples. The overall correction accuracy of the three channels is better than one-third of the sampling interval. [ABSTRACT FROM AUTHOR]

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.

A Mars Surface Composition Detector (MarSCoDe) instrument mounted on Zhurong rover of Tianwen-1, adopts Laser-Induced Breakdown Spectroscopy (LIBS), with no sample preparation or dust and coatings ablation required, to conduct rapid multi-elemental analysis and characterization of minerals, rocks and soils on the surface of Mars. To test the capability of MarSCoDe LIBS measurement and quantitative analysis, some methods of multivariate analysis on olivine samples with gradient concentrations were inspected based on the spectra acquired in a Mars-simulated environment before the rover launch in 2020. Firstly, LIBS spectra need preprocessing, including background subtraction, random signal denoising, continuum baseline removal, spectral drift correction and wavelength calibration, radiation calibration, and multi-channel spectra subset merging. Then, the quantitative analysis with univariate linear regression (ULR) and multivariate linear regression (MLR) are performed on the characteristic lines, while principal component regression (PCR), partial least square regression (PLSR), ridge, least-absolute-shrinkage-and-selection-operator (LASSO) and elastic net, and nonlinear analysis with back-propagation (BP) are conducted on the entire spectral information. Finally, the performance on the quantitative olivine analyzed by MarSCoDe LIBS is compared with the mean spectrum and all spectra for each sample and evaluated by some statistical indicators. The results show that: (1) the calibration curve of ULR constructed by the characteristic line of magnesium and iron indicates the linear relationship between the spectral signal and the element concentration, and the limits of detection of forsterite and fayalite is 0.9943 and 2.0536 (c%) analyzed by mean spectra, and 2.3354 and 3.8883 (c%) analyzed by all spectra; (2) the R2 value on the calibration and validation of all the methods is close to 1, and the predicted concentration estimated by these calibration models is close to the true concentration; (3) the shrinkage or regularization technique of ridge, LASSO and elastic net perform better than the ULR and MLR, except for ridge overfitting on the testing sample; the best results can be obtained by the dimension reduction technique of PCR and PLSR, especially with PLSR; and BP is more applicable for the sample measured with larger spectral dataset. [ABSTRACT FROM AUTHOR]

As an important part of China’s first Mars exploration mission, the Tianwen-1 relay communication system is responsible for providing efficient and reliable communication services between the lander-rover and orbiter, and supporting the completion of exploration mission during the entry, descent and landing (EDL)phase and on Mars’ surface. The relay communication scheme of Tianwen-1 probe with ultra high requency (UHF) band is introduced. The composition, specifications and design method of the critical part of the relay communication system are given. The results of on-orbit flight data are analyzed. The flight verification results show that the newly developed relay communication system of Tianwen-1 probe successfully achieves the exploration mission objectives. Its design, implementation and application also provide technical reference for the subsequent development of China’s deep space relay communication system. [ABSTRACT FROM AUTHOR]

Mars Orbiter Subsurface Investigation Radar (MOSIR) is carried by China's first Mars probe, Tianwen‐1 orbiter, investigating the Martian subsurface stratification. Surface clutter from topography off‐nadir will overlap with the subsurface echoes, which affects the recognition of Martian subsurface reflections. Surface clutter simulation can effectively distinguish the nadir and off‐nadir radar echoes. In this paper, we choose the facet method to model the Mars surface topography and combine the roughness parameter with the radar backscatter function. We also provide an analytic expression of the echo phase considering the distance variation in the whole facet. The Chinese first Mars landing site is on Utopia Planitia, which is also one of the key investigating regions of MOSIR. Therefore, we also carried on surface clutter simulation of this region and generated simulation radargram with the Chirp Scaling algorithm. Furthermore, we use the contrast method to compensate for ionospheric error introduced by the NeMars Mars ionosphere model. Our surface clutter simulation program will significantly support MOSIR subsurface investigation, and provide a chance to verify the related data processing. Key Points: Wavelength‐scale surface roughness is introduced into the proposed surface clutter simulation methodThe proposed surface clutter simulation method is applied to verify the ionospheric error correction approachEcho peak power simulated by the proposed method is in good agreement with MRO SHARAD radargram [ABSTRACT FROM AUTHOR]

Delta-Differential One-Way Ranging (DeltaDOR) is widely used in deep spacecraft navigation, and cross support could enhance navigation accuracy with more interferometry baselines and longer baseline. In China Mars mission Tianwen-1, formal joint cross-support interferometry tracking between China Satellite Launch and TT&C General (CLTC) and European Space Operations Center (ESOC) under commercial contract was conducted around the critical stages of the mission, such as Mars orbit insertion. Cross-support interferometry is a new challenge to CLTC, as the correlator for routine DeltaDOR measurements do not fit for cross support, because of observable definition, blind station clock searching, and so on. This paper discusses the new method and algorithm adopted in joint cross support, especially for spacecraft tone signal processing and clock estimation when correlating with the data of two stations from different agencies. Results of the cross-support interferometry tracking activities are also analyzed. Observables from CLTC and ESOC are consistent with each other, and the difference in observables is in the order of tens of ps. All the baselines are induced to evaluate the accuracy of the spacecraft orbit determined and predicted by CLTC, and the DeltaDOR residuals have a root-mean-square (RMS) better than 0.5 ns (the goal is 1 ns), which could enhance the confidence of the orbit accuracy and the effectiveness of control parameters during critical orbit operation. [ABSTRACT FROM AUTHOR]

The high-resolution imaging camera (HiRIC) onboard China’s Tianwen-1 Mars probe aims to acquire detailed imagery of the Martian surface to comprehensively investigate its topography and geomorphology. The HiRIC is a pushbroom camera comprising three CCDs to simultaneously achieve submeter resolution and a large swath. However, processing HiRIC images using the conventional photogrammetric workflow is difficult due to the large shifts and narrow overlapping among the CCD lines. This article presents a novel approach for photogrammetric processing of HiRIC images for precision topographic mapping that incorporates: 1) the fitting of the initial rational polynomial coefficients (RPCs) of images from the HiRIC position and pointing data; 2) a deep-learning-based method for tie-point matching between adjacent CCD images and cross-orbit images; 3) the bundle adjustment of multiple CCD images for tripled-epipolar image generation to ensure inner orbit consistency; 4) the block adjustment of multiple orbit images to ensure cross-orbit consistency; and 5) dense image matching and space intersection based on the refined RPCs to generate digital elevation models (DEMs). Experimental analyses were conducted using HiRIC images covering the landing region of the Zhurong rover. The results revealed that subpixel accuracy was achieved for image residuals among multiple-CCD or multiple-orbit images. Comparison with the reference data (HiRISE and MOLA DEMs) revealed a mean deviation of less than 7 m in terms of the geometric accuracy and the subtle topographic details of the HiRIC DEM. The presented approach offers a reliable solution for using the new dataset of HiRIC imagery for Mars topographic mapping. [ABSTRACT FROM AUTHOR]

The radio-occultation technique can provide vertical profiles of planetary ionospheric and atmospheric parameters, which merit the planetary-climate and space-weather scientific research so far. The Tianwen-1 one-way single-frequency radio-occultation technique was developed to retrieve Mars ionospheric and atmospheric parameters. The first radio-occultation event observation experiment was conducted on 5 August 2021. The retrieved excess Doppler frequency, bending angle, refractivity, electron density, neutral mass density, pressure and temperature profiles are presented. The Mars ionosphere M1 (M2) layer peak height is at 140 km (105 km) with a peak density of about 3.7 × 1010 el/m3 (5.3 × 1010 el/m3) in the retrieved electron-density profile. A planetary boundary layer (−2.35 km~5 km), a troposphere (temperature decreases with height) and a stratosphere (24 km–40 km) clearly appear in the retrieved temperature profile below 50 km. Results show that Tianwen-1 radio occultation data are scientifically reliable and useful for further Mars climate and space-weather studies. [ABSTRACT FROM AUTHOR]

On 15 May 2021, the Zhurong rover of China's first Mars mission, Tianwen-1 (TW-1), successfully landed in southern Utopia Planitia on Mars. Various landforms were present in the landing area, and this area recorded a complex geological history. Cones are one of the typical landforms in the landing area and Utopia Planitia, and they have a great significance to the local geological processes due to the diversity of their origins. Using High-Resolution Imaging Camera (HiRIC) images collected by the TW-1 orbiter, we identified a total of 272 well-preserved circular cones in the landing area. Detailed surveys of their spatial distribution, morphological characteristics, and morphometric parameters were conducted. A preliminary analysis of the surface characteristics of these cones also provides additional information to strengthen our understanding of them. The results of the high-resolution topographic analysis show that the cone heights are in the range of 10.5–90.8 m and their basal diameters range from 178.9–1206.6 m. We compared the morphometric parameters of the cones in the landing area with terrestrial and Martian analogous features and found that our measured cones are consistent with the ranges of mud volcanoes and also a small subset of igneous origin cones. However, the result of spatial analysis is more favorable to mud volcanoes, and the lower thermal inertia of the cones in the landing area compared to their surrounding materials is also a typical characteristic of mud volcanoes. Based on current evidence and analysis, we favor interpreting the cones in the TW-1 landing area as mud volcanoes. [ABSTRACT FROM AUTHOR]

The spatial and temporal distribution of dust devils (DDs) in the two pre-selected landing regions (ZA and ZB) of the Tianwen-1 mission in southern Utopia Planitia have been investigated by using images from the Context Camera (CTX) of the Mars Reconnaissance Orbiter (MRO). From the images of the regions in 8 Martian years, no DD was found in ZA, while 77 DDs were found in ZB. The observed DDs are mainly distributed in the northeastern part of ZB. The temporal variation in the observed DDs shows a prominent two-peak pattern in their local early spring and late summer. The size and height of the observed DDs have also been evaluated from the images, and they show a similar temporal variation as the occurrence. To investigate the possible conditions pertinent to these observed patterns of DD distribution, some analysis based on the thermodynamic theory of heat engines was performed using the output of the Mars climate model, MarsWRF. The spatial and temporal distribution of the simulated DDs are generally consistent with the observation, with significantly more DDs in ZB. Analysis of the model results suggests that the spatial distributions of the predicted DDs are mainly related to the distribution of sensible heat flux, which, in turn, is mainly determined by the surface-to-air temperature difference. The difference in DDs between ZA and ZB (more DDs in ZB) is dominated by the difference in sensible heat flux, which, in turn, is mainly related to the spatial variation of surface albedo. [ABSTRACT FROM AUTHOR]

On the great journey to Mars, China's first planetary exploration mission, the Tianwen-1 came within 26 million kilometers of Mars from 31 October 2020 to 25 January 2021 and was getting closer to its destination, the red planet, in search of answers to the cataclysmic climate change that occurred in Martian history. Both the escape of the Martian atmosphere and the loss of surface water were firmly influenced by solar activities. Tianwen-1 provided a unique chance to depict the solar wind streams between Earth and Mars during the minimum of Solar Cycle 25. During the three-month cruise phase of Tianwen-1, the solar wind flows were successively observed at Earth, Tianwen-1, and Mars. After the field of view correction and noise reduction, the solar wind velocity and density measured by Tianwen-1 show good agreement with those at Earth and Mars. The results indicate that the performance of the ion analyzer onboard the Tianwen-1 orbiter is reliable and stable. It is worth looking forward to the joint observations of ion escape with other Mars probes in the following Martian years. [ABSTRACT FROM AUTHOR]

The Chinese Mars rover Zhurong onboard the Tianwen‐1 probe successfully landed on Mars in May 2021. Here, we report our efforts in selecting a landing site for Zhurong within a pre‐identified landing region in southern Utopia Planitia. Using the high‐resolution images collected by a camera onboard the Tianwen‐1 orbiter, the landing region was analyzed in detail in terms of surface slopes, crater densities and rock abundances, which enabled the optimized determination of a landing ellipse (56 × 22 km for the major and minor axes) with minimum hazards and assisted the successful landing of the Zhurong rover. We also characterized the landing site and region after landing. Surface images captured by a camera onboard the Zhurong rover revealed a low rock abundance of approximately 4% at the landing site, similar to the rock measurements from orbital data before landing. Images of the surface features and a hole excavated by the pulsed retrorockets beneath the lander suggested a shallow regolith structure with a surficial layer of dust and sand over a layer of duricrust, and brecciated/fragmented rocks and bedrocks beneath. Crater size‐frequency distribution analysis indicated that the landing region might have experienced multiple episodes of resurfacing. Plain Language Summary: The Chinese Mars rover Zhurong onboard the Tianwen‐1 probe successfully landed on Mars in May 2021. Here, we report our efforts in selecting a landing site for Zhurong within a pre‐identified landing region in southern Utopia Planitia. Using the high‐resolution images collected by a camera onboard the Tianwen‐1 orbiter, the landing region was analyzed in detail in terms of surface slopes, crater densities and rock abundances, which enabled the optimized determination of a landing site with minimum hazards and assisted the successful landing of the Zhurong rover. We also characterized the landing site and region after landing. Surface images captured by a camera onboard the Zhurong rover revealed a low rock abundance at the landing site. Images of the surface features and a hole excavated by the pulsed retrorockets beneath the lander suggest a shallow regolith structure with a surficial layer of dust and sand over a layer of duricrust, and fragmented rocks and bedrocks beneath. Crater size‐frequency distribution analysis suggested that the landing region might have experienced multiple episodes of resurfacing. Key Points: Landing site selection for the Zhurong rover within a pre‐identified landing region in southern Utopia PlanitiaSurface and shallow subsurface properties at the Zhurong landing siteMultiple episodes of resurfacing at the landing region from crater size‐frequency distribution analysis [ABSTRACT FROM AUTHOR]

China’s first Mars probe Tianwen-1 has successfully landed on the southern Utopia Planitia of Mars on May 15, 2021. The Zhurong rover is first equipped with a full-polarimetric Mars Rover Penetrating Radar (FP-RoPeR) system, aiming to map the subsurface fine structure and to find the potential underground water ice. However, different from the previous water ice detection of orbital radar, the FP-RoPeR signals will be affected by the induced field rotation (IFR) if electromagnetic (EM) waves propagate through rough interfaces. Therefore, in this article, we assess the IFR effects from rough interfaces on the circular polarization ratio (CPR) response of FP-RoPeR data, which is a significant parameter for water ice detection. The theoretical computation and numerical validation indicate that the depth, the number of rough interfaces, and relative permittivity are three vital parameters that affect the IFR effects; depth plays a more important role than the other two for FP-RoPeR system. The CPR estimation result will be with greater error in the shallow region (0–1 m). The relative error in the region of depth greater than 1 m can be guaranteed to be under 10%. [ABSTRACT FROM AUTHOR]

The background and scientific objectives of the Mars Climate Station (MCS) for Tianwen-1 are introduced, accompanied by a comparative review of the status of related meteorological observation missions and of advanced sensing technologies. As one of the China Tianwen-1 Mission’s principal scientific payloads, the MCS contains four measurement sensors and one electronic processing unit that are specially designed to measure local temperature, pressure, wind, and sound on the Martian surface. The MCS’s measurement principles, technical schemes, ground calibration techniques, and adaptability evaluation to the Mars surface environment of MCS are introduced in details. The conclusion presents measurement performance specifications of the MCS, based on ground test results, that will provide guidance to future research based on data from the Tianwen-1 and later Mars missions.

The first Mars exploration mission of China (Tianwen-1) is scheduled to be launched in 2020; a charged particle telescope, the Mars Energetic Particle Analyzer (MEPA), is carried as one of the payloads on the orbiter. The MEPA is designed to measure solar energetic particles (SEPs) and galactic cosmic rays (GCRs) in the near-Mars space and in the transfer orbit from Earth to Mars. Before the launch, the MEPA was calibrated in ground experiments with radioactive sources, electronic pulses, and accelerator beams. The calibration parameters, such as energy conversion constants, threshold values for the triggers, and particle identification criteria, were determined and have been stored for onboard use. The validity of the calibration parameters has been verified with radioactive sources and beams. The calibration results indicate that the MEPA can measure charged particles reliably, as designed, and that it can satisfy the requirements of the Tianwen-1 mission.

As one of the seven scientific payloads on board the Tianwen-1 orbiter, the Mars Orbiter Magnetometer (MOMAG) will measure the magnetic fields of and surrounding Mars to study its space environment and the interaction with the solar wind. The instrument consists of two identical triaxial fluxgate magnetometer sensors, mounted on a 3.19 meter-long boom with a seperation of about 90 cm. The dual-magnetometers configuration will help eliminate the magnetic field interference generated by the spacecraft platform and payloads. The sensors are controlled by an electric box mounted inside the orbiter. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 10,000 nT per axis) with a resolution of 1.19 pT. Both magnetometers sample the ambient magnetic field at an intrinsic frequency of 128 Hz, but will operate in a model with alternating frequency between 1 and 32 Hz to meet telemetry allocations.

Tianwen-1 is China's first deep space probe to explore Mars with the goal of orbiting, landing and roving. This paper presents the orbit determination process and result of the probe in the phase of Earth-Mars trajectory in detail. Orbit determination is carried out based on the tracking data obtained by CDSN (Chinese Deep Space Network) and CVN (Chinese VLBI Network). The results show that the residual RMS of range, Doppler, VLBI delay and delay rate data are about 0.28 m, 0.10 mm/s, 0.12 ns and 0.34 ps/s, respectively. Compared with the previous missions in Chinese Lunar Exploration Program (CLEP), the accuracy of VLBI data is significantly improved. The analysis shows that the prediction error of EOP (Earth Orientation Parameter) and the planetary ephemerides lead to the difference of orbit solution. With the increasing distance between the spacecraft and Earth, the EOP prediction error has a certain influence to the orbit determination accuracy. The difference in orbit solutions due to EOPs' prediction error before MOI (Mars Orbit Insertion) is about 300 m. Moreover, the orbit difference is about 200 m using different planetary ephemerides (DE421/DE436). Orbit overlapping results show the position and velocity error of Tianwen-1 are less than 2 km and 1 cm/s, respectively. During the approaching phase, the error ellipse in B-plane shows that σ SMAA = 389.40 m, σ SMIA = 140.88 m (1σ). [ABSTRACT FROM AUTHOR]

We used imaging, laser altimeter and thermal infrared data to map a 0.5 by 0.5° area containing the landing site of the Zhurong rover of the Tianwen‐1 mission. We analyzed the regional topography and thermophysical characteristics, and identified and characterized cones, impact craters, polygonal troughs, ridges and aeolian bedforms. An absolute model age of 757 ± 66 Ma was obtained for the major unit dominating the study area, younger than previous geological mapping results. We propose several targets of high scientific interest for Zhurong and a stratigraphic model composed of five layers (from bottom to top: Noachian basement, Early Hesperian volcanic ridged plains, Vastitas Borealis Formation materials, rocky materials and loose materials). The geomorphic features identified, the proposed stratigraphy and the regional geological evolution scenario set the stage for the Zhurong rover to continue to carry out its exploration of Mars. Plain Language Summary: Tianwen‐1 is China's first independent Mars mission. It consists of an orbiter and a lander and a rover (Zhurong). The Zhurong rover successfully touched down on the surface of Mars on May 15, 2021. The landing site lies in southern Utopia Planitia, in the northern lowlands of Mars. We identified various geomorphologic features within an area of 0.5 by 0.5° centered around the landing site of the Zhurong rover using image, elevation and temperature remote sensing data. We propose a history and geological evolution of the region to set the stage for the Zhurong rover exploration and analysis. Key Points: We conducted detailed geological mapping of the Zhurong landing region on MarsHigh scientific interest targets for Zhurong rover including cones, pitted‐wall craters, aeolian bedforms, polygons, and ridges are proposedA middle Amazonian surface age is suggested and a five‐layer stratigraphic model of the Zhurong landing region is proposed [ABSTRACT FROM AUTHOR]