In a Nature Physics report published in late September 2024[1],a team of scientists and engineers at Sandia National Laboratories(Albuquerque,NM,USA)described the results of a laboratory experiment showing that a nucl...In a Nature Physics report published in late September 2024[1],a team of scientists and engineers at Sandia National Laboratories(Albuquerque,NM,USA)described the results of a laboratory experiment showing that a nuclear blast could create a burst of X-rays powerful enough to change the path of a large asteroid that might one day be on a collision course with Earth.展开更多
The surface particle size and distribution characteristics of celestial bodies (e.g.,the Moon,asteroids,etc.) will affect the interpretation of hyperspectral remote sensing data and the implementation of sampling miss...The surface particle size and distribution characteristics of celestial bodies (e.g.,the Moon,asteroids,etc.) will affect the interpretation of hyperspectral remote sensing data and the implementation of sampling missions.Currently,the estimation of the surface particle sizes is mainly focusing on interpreting the thermal inertia with the infrared spectral data from ground-based or space telescopes,but this method show distinct errors compared with the imaging results of the orbiter.By analyzing some thermal infrared spectral data,a relationship between the particle sizes of the main rockforming minerals (e.g.pyroxene,feldspar,olivine) and the slopes of their thermal infrared spectrum was found.Based on this relationship,a preliminary model for estimating the grain sizes (~30–300μm) of lunar or S-type asteroids’surfaces which are silicate minerals dominated was established,and the correlation coefficients (R^(2)) for most of the rock-forming minerals were better than 90%.Six observational datasets of natural lunar and terrestrial samples are used to validate the model,and the results show a systematical overestimation of the ground-truth particle sizes,the potential causes are analyzed and an additional correction is used to eliminate the overestimation of the particle size prediction.These results are expected to provide guidance for interpretation of lunar and S-type asteroid surface sampling and spectral data.展开更多
Flexible lander,composed of multiple nodes connected by flexible material,can reducethe bouncing and overturning during the asteroid landing.To satisfy the complex constraints inthe node cooperation of the flexible la...Flexible lander,composed of multiple nodes connected by flexible material,can reducethe bouncing and overturning during the asteroid landing.To satisfy the complex constraints inthe node cooperation of the flexible landing,an intelligent cooperative guidance method is pro-posed.The method consists of a double-layer cooperative guidance structure,a guidance parameterdetermination approach,and an action priority strategy.The double-layer contains a basic guid-ance used to satisfy the terminal state constraints,and a compensatory guidance used to satisfythe lander's attitude constraint.For the compensatory guidance,the parameters are determinedby multi-agent system,which are trained according to the performance index of flexible landing tra-jectories.The action priority strategy is used to reduce the detrimental effect of parameter inconsis-tency on the node cooperation.The simulation of flexible landing shows that the cooperativeguidance method is effective in improving the landing accuracy while satisfying the constraints.Meanwhile,the method is robust to the disturbance in the navigation and control.展开更多
At the end of the Cretaceous period,66 million years ago,the 7−19 km diameter Chicxulub asteroid hit the Yucatan Peninsula in Mexico,triggering global catastrophic environmental changes and mass extinction.The contrib...At the end of the Cretaceous period,66 million years ago,the 7−19 km diameter Chicxulub asteroid hit the Yucatan Peninsula in Mexico,triggering global catastrophic environmental changes and mass extinction.The contributions of this event towards changes in plate and plume geodynamics are not fully understood.Here we present a range of geological observations indicating that the impact marked a tectonic turning point in the behavior of mantle plume and plate motion in the Caribbean region and worldwide.At a regional scale,the impact coincides with the termination of seafloor spreading in the Caribbean Ridge.Shortly after the Cretaceous-Paleogene transition,magmatism associated with the Caribbean Large Igneous Province waned,and intensive Paleogene volcanism was initiated.These events happened synchronously with anomalously high mid-ocean ridge magmatism worldwide and an abrupt change in the relative motion of the South American and North American tectonic plates.The evidence for such abrupt changes in plate kinematics and plume behavior raises the possibility that the Chicxulub impact triggered a chain of effects that modified melt reservoirs,subducting plates,mantle flows,and lithospheric deformation.To explain how an asteroid impact could modify tectonic behavior,we discuss two end-member mechanisms:quasi-static and dynamic triggering mechanisms.We designed a numerical model to investigate the strain field and the relative plate motion before and after the impact.The model predicts an enhanced deformation associated with the impact,which surficially tapers off∼500 km from the crater.The impact modifies the subjacent mantle flow field,contributing to long-term mantle-driven dynamic changes.Additionally,deformation associated with seismic effects may have contributed to far-field effects and global changes.We conclude that large asteroid impacts,such as the Chicxulub collision,could trigger cascading effects sufficient to disrupt and significantly modify plate geodynamics.展开更多
Near-Earth Asteroids posed a threat to human civilization,making their monitoring crucial.As the demand for asteroid detection technology increased,precise detection of these celestial bodies became an urgent task to ...Near-Earth Asteroids posed a threat to human civilization,making their monitoring crucial.As the demand for asteroid detection technology increased,precise detection of these celestial bodies became an urgent task to understand their characteristics and assess potential impact risks.To improve asteroid detection accuracy and efficiency,we proposed an advanced image processing method and a deep learning network for automatic asteroid detection.Specifically,we aligned star clusters and overlaid images to exploit asteroid motion rates,transforming them into object-like trajectories and improving the signal-to-noise ratio.This approach created the Asteroid Trajectory Image Data set under various conditions.We modified CenterNet2 network to develop AstroCenterNet by integrating Multi-channel Histogram Truncation for feature enhancement,using the SimAM attention mechanism to expand contextual information and suppress noise,and refining Feature Pyramid Network to improve low-level feature detection.Our results demonstrated a detection accuracy of 98.4%,a recall of 97.6%,a mean Average Precision of 94.01%,a false alarm rate of 1.6%,and a processing speed of approximately 17.86 frames per second,indicating that our method achieves high precision and efficiency.展开更多
Implementing the flyby to Near-Earth Asteroids (NEAs) with the potential impact risks to the Earth allows for obtaining detailed physical parameters, thereby supporting the high-precision orbit prediction and planetar...Implementing the flyby to Near-Earth Asteroids (NEAs) with the potential impact risks to the Earth allows for obtaining detailed physical parameters, thereby supporting the high-precision orbit prediction and planetary defense strategy. Different from those conducted asteroid flyby missions, in the 12th China Trajectory Optimization Competition (CTOC-12), a NEAs flyby trajectory design problem using reusable probes that depart from a Lunar Distant Retrograde Orbit (DRO) station in the cislunar space was released. The objective was flyby to as many NEAs as possible using up to 20 probes within a total of 10 years. The ∑ team proposed a solution that can explore 47 NEAs using 11 probes, ranking the first in the competition. In this paper, the methods and results from the winning team are introduced, including mission analysis and preliminary design, and low-energy transfer trajectory optimization. In particular, a round-trip trajectory is divided into three phases: deep space transfer, indirect transfer between the Earth to DRO, and DRO phasing and rendezvous. With the combination of global optimization and local optimization algorithms, the required velocity increments to change the orbital planes are effectively reduced, thus increasing the number of the explored NEAs. The final solution of our team is presented and the results are compared with those of the top three teams. The competition demonstrates that the regularization of flyby missions from the cislunar space to explore NEAs with the potential impact risks to the Earth is the feasible and promising.展开更多
Sent out at 1:31am GMT+8 on May 29 by a Long March-3B carrier rocket from the Xichang Satellite Launch Center in Sichuan province,China,Tianwen-2,the second mission of China’s Planetary Exploration Program,correctly ...Sent out at 1:31am GMT+8 on May 29 by a Long March-3B carrier rocket from the Xichang Satellite Launch Center in Sichuan province,China,Tianwen-2,the second mission of China’s Planetary Exploration Program,correctly entered the transfer trajectory toward an asteroid named 2016HO3 after flying for 18 minutes.Its solar wings unfolded properly,signaling a successful start,and primed for the next stage of its mission.展开更多
The SiTian project,with its vast field of view,will become an ideal platform for scientific research on asteroids.In this study,we develop a pipeline to analyze the photometry of asteroids and derive their periods fro...The SiTian project,with its vast field of view,will become an ideal platform for scientific research on asteroids.In this study,we develop a pipeline to analyze the photometry of asteroids and derive their periods from the data collected by the SiTian pathfinder project Mini-SiTian(MST).The pipeline is applied to the MST f02 region,an MST test region with a sky area of 2°.29×1°.53.Rotation periods of 22 asteroids are derived by the obtained light curve analysis.Among them,there are eight asteroids available in the Asteroid Lightcurve Photometry Database(ALCDEF),and six of them with more photometric points(>200)that have similar period parameters as the ones in ALCDEF.Additionally,the periods for 14 of these asteroids are newly obtained and are not listed in ALCDEF.This study demonstrates the feasibility of asteroid photometric research by the SiTian project.It shows that future observations from the SiTian project will provide even more photometry of asteroids,significantly increasing the number of available light curves.The potential vast photometric data on asteroids will help us to further understand the physics of asteroids,their material composition,and the formation and evolution of the solar system.展开更多
The perihelion of long-period comets places them near the Sun so they may exhibit activity.Before 2013 LU28 reached its perihelion,we performed a continuous observation to detect possible activity.Using the Lijiang 2....The perihelion of long-period comets places them near the Sun so they may exhibit activity.Before 2013 LU28 reached its perihelion,we performed a continuous observation to detect possible activity.Using the Lijiang 2.4 m telescope with a Johnson R filter,we measured the brightness of 2013 LU28 from 2024 January 3 to April 13.The instrumental magnitudes were subsequently transformed into the Pan-STARRS r system.Due to the noticeable descending trend in the absolute magnitude,we verified the cometary activity and constrained some photometric properties of 2013 LU28.Consequently,the increased cross-sectional area had a rate of 42.8 km^(2)day^(−1),and the corresponding mass-loss rate was 2.64 kg s^(−1)with the assumption of a dust-particle size a=10 mm and the densityρ=400 kg m^(−3).We estimated the nucleus radius as 0.11■r_(n)■0.21 km for CO sublimation and 0.20■r_(n)■0.71 km for CO_(2)sublimation and the grain size of 2013 LU28 was ac;117.95μm for CO and ac■7.57μm for CO_(2).The long-term observations provided in this paper will offer significant value for investigating the mechanisms driving the activity of 2013 LU28.展开更多
Magnetite-ilmenite pairs in meteorites serve as reliable thermometers and oxygen fugacity (fO_(2)) indicators for constraining both nebular conditions and thermal metamorphic histories.While CK and CV chondrites exhib...Magnetite-ilmenite pairs in meteorites serve as reliable thermometers and oxygen fugacity (fO_(2)) indicators for constraining both nebular conditions and thermal metamorphic histories.While CK and CV chondrites exhibit nearly identical petrological characteristics and oxygen isotope compositions,our analysis of NWA 16813 reveals it records the highest fO_(2)(log fO_(2)=-20.51 (589.34°C)-log fO_(2)=-14.21 (608.63°C))yet measured among these meteorites.This finding provides critical evidence that CK and CV chondrites experienced fundamentally different redox conditions during their formation.The fO_(2)data from NWA16813,combined with its distinct petrological and mineralogical features,strongly suggest that CK and CV chondrites originated from chemically separate reservoirs in the protoplanetary disk despite their apparen similarities.展开更多
The shapes and rotation states(periods and pole orientations)of main-belt asteroids are important for understanding their formation and evolution.In order to obtain sufficient photometric data covering different appar...The shapes and rotation states(periods and pole orientations)of main-belt asteroids are important for understanding their formation and evolution.In order to obtain sufficient photometric data covering different apparitions for asteroid(81)Terpsichore,ground-based photometric observations in 2020 and 2021 were carried out.By combining published and newly obtained photometric data,we calculated the shape and spin parameters for(81)Terpsichore using the convex inversion method.With this method,we have derived a best fitted pole orientation—(22.2±_(3.1)^(3.3°),17.5±_(5.5)^(10.8°))with a spin period of 10.94±_(0.01)^(0.01)h.Based on the derived convex shape of(81)Terpsichore,we have fitted the H,G+1,G_(2)phase function using the calibrated TESS data and Gaia data after accounting for the lightcurve amplitude correction.As a result,we have derived its absolute magnitude H=8.68±_(0.19)^(0.22)mag with corresponding phase function parameters G_(1)=0.82±_(0.10)^(0.09)and G_(2)=0.02±_(0.02)^(0.03).展开更多
As the second of Earth's Trojan asteroids, 2020 XL_(5) is worthy of rendezvous and even sample return missions in many aspects. In this paper, a rendezvous mission to Earth's second Trojan asteroid 2020 XL_(5)...As the second of Earth's Trojan asteroids, 2020 XL_(5) is worthy of rendezvous and even sample return missions in many aspects. In this paper, a rendezvous mission to Earth's second Trojan asteroid 2020 XL_(5) is proposed.However, due to its high inclination and large eccentricity, direct impulsive transfer requires large amounts of fuel consumption. To address this challenge, we explore the benefits of electric propulsion and multi-gravity assist techniques for interplanetary missions. These two techniques are integrated in this mission design. The design of a low-thrust gravity-assist(LTGA) trajectory in multi-body dynamics is thoroughly investigated,which is a complex process. A comprehensive framework including three steps is presented here for optimization of LTGA trajectories in multi-body dynamics. The rendezvous mission to 2020 XL_(5) is designed with this three-step approach. The most effective transfer sequence among the outcomes involves Earth–Venus–Earth–Venus-2020 XL_(5). Numerical results indicate that the combination of electric propulsion and multi-gravity assists can greatly reduce the fuel consumption, with fuel consumption of 9.03%, making it a highly favorable choice for this rendezvous mission.展开更多
Determining asteroid properties provides valuable physical insights but inverting them from photometric lightcurves remains computationally intensive.This paper presents a new approach that combines a simplified Celli...Determining asteroid properties provides valuable physical insights but inverting them from photometric lightcurves remains computationally intensive.This paper presents a new approach that combines a simplified Cellinoid shape model with the Parallel Differential Evolution(PDE)algorithm to accelerate inversion.The PDE algorithm is more efficient than the Differential Evolution algorithm,achieving an extraordinary speedup of 37.983 with 64 workers on multicore CPUs.The PDE algorithm accurately derives period and pole values from simulated data.The analysis of real asteroid lightcurves validates the method’s reliability:in comparison with results published elsewhere,the PDE algorithm accurately recovers the rotational periods and,given adequate viewing geometries,closely matches the pole orientations.The PDE approach converges to solutions within 20,000 iterations and under one hour,demonstrating its potential for large-scale data analysis.This work provides a promising new tool for unveiling asteroid physical properties by overcoming key computational bottlenecks.展开更多
In history,the Earth has encountered frequent and massive impacts.Until today,it is still a collided target for Potentially Hazardous Objects(PHOs),gradually making planetary defense a concerned and important research...In history,the Earth has encountered frequent and massive impacts.Until today,it is still a collided target for Potentially Hazardous Objects(PHOs),gradually making planetary defense a concerned and important research topic in the field of aerospace science.Against this background,this work clarifies and discusses some important scientific issues and various critical technologies of planetary defense.First,the current status of planetary defense research is summarized.Subsequently,the classification and characteristics of PHOs are introduced,focusing on their potential impact on planetary defense and related scientific research issues.For the purpose of protecting the Earth and maintaining space safety,the monitoring and characterization,deflection,and mitigation of PHOs have basically occupied all the attention of planetary defense researchers.Therefore,the critical technologies in planetary defense are discussed from these three aspects,and are also compared and analyzed in depth.Based on the current research progress in planetary defense,the challenges for planetary defense are discussed,and future development directions are also analyzed.Finally,a summary of the entire study is provided.展开更多
The characteristics of asteroids are vital parameters for planning asteroid exploration missions.These characteristics have been explored in close range for some typical asteroids,and are summarized in the article.Thi...The characteristics of asteroids are vital parameters for planning asteroid exploration missions.These characteristics have been explored in close range for some typical asteroids,and are summarized in the article.This allows estimates of the characteristics of asteroid 2016HO_(3),the target of the first Chinese asteroid exploration mission,Tianwen 2.We obtain 80 characteristic parameters in 9 categories and analyze their impacts on the mission.By comparing three close-range exploration modes,we provide advantages and disadvantages of each,and propose suitable methods for the exploration of 2016HO_(3).Owing to the weak gravity and small size of 2016HO_(3),a combination of multiple hovering positions and active orbiting is recommended for scientific exploration.展开更多
A compilation of many different kinds of natural scientific investigations and their interrelations as well as their collective interpretation are necessary to understand past, presence and future of the Earth’s syst...A compilation of many different kinds of natural scientific investigations and their interrelations as well as their collective interpretation are necessary to understand past, presence and future of the Earth’s system adequately. This has been tried with somehow surprising results in this paper. Milky Way related cycles on Earth of 150 Myr duration as observed for the Phanerozoic Eon are obviously not dominant in the Proterozoic Eon. Only a very weak galactic signal due to periodic occurrences of phosphorous may be present that has entered the Earth from exploding stars. The Phanerozoic can be defined as an eon with very sensitive geophysical, geological, meteorological and biological reactions. The accelerated reactions from a 400 Myr to a 300 Myr cycle of mineral ages and continental tectonics include a generally high surface temperature with glacial interruptions, high oxygen and ozone values in the atmosphere, increase of the strength of the magnetic field and the rise of the asteroid impact rate witness those sensitives. It cannot be excluded after analyzing all related data that 1) Asteroid impacts stabilized and strengthened the Earth’s magnetic field, 2) apparently the acceleration of geodynamic processes on Earth after weakening of the dynamics of Earth’s core (geodynamo) is Milky Way supported, 3) the life spending biologically produced oxygen and its ozone derivative can influence Earth’s climate significantly, and 4) somehow time coordinated events like asteroid impacts, Earth’s core dynamics, nearby exploding stars, solar system pathway through dusty spiral arms, plate tectonics, a speculative companion of the Sun (or something else) and oxygen production via photosynthesis were essential ingredients for the remarkable success of life on Earth.展开更多
BACKGROUND Systemic lupus erythematosus(SLE)patients are extremely susceptible to opportunistic infections due to glucocorticoid and immunosuppressive treatments,which often occur in the respiratory system,the urinary...BACKGROUND Systemic lupus erythematosus(SLE)patients are extremely susceptible to opportunistic infections due to glucocorticoid and immunosuppressive treatments,which often occur in the respiratory system,the urinary system and the skin.However,multiple cerebral infections are rarely reported and their treatment is not standardized,especially when induced by a rare pathogen.CASE SUMMARY A 46-year-old woman was treated with glucocorticoid and immunosuppressant for SLE involving the hematologic system and kidneys(class IV-G lupus nephritis)for more than one year.She was admitted to hospital due to headache and fever,and was diagnosed with multiple cerebral abscesses.Brain enhanced magnetic resonance imaging showed multiple nodular abnormal signals in both frontal lobes,left parietal and temporal lobes,left masseteric space(left temporalis and masseter region).The initial surgical plan was only to remove the large abscesses in the left parietal lobe and right frontal lobe.After surgery,based on the drug susceptibility test results(a rare pathogen Nocardia asteroides was found)and taking into consideration the patient’s renal dysfunction,a multi-antibiotic regimen was selected for the treatment.The immunosuppressant mycophenolate mofetil was discontinued on admission and the dose of prednisone was reduced from 20 mg/d to 10 mg/d.Re-examination at 3 mo post-surgery showed that the intracranial lesions were reduced,the edema around the lesions was absorbed and dissipated,and her neurological symptoms had disappeared.The patient had no headaches or other neurological symptoms and lupus nephritis was stable during the 2-year follow-up period.CONCLUSION In this report,we provide reasonable indications for immunosuppression,anti-infective therapy and individualized surgery for an SLE patient complicated with multiple cerebral abscesses caused by a rare pathogen,which may help improve the diagnosis and treatment of similar cases.展开更多
Most cases of nocardiosis are seen in immunocompromised patients. Primary lymphocutaneous is a relatively uncommon presentation of this disease that may also occurs in normal hosts. Diagnosing this infection requires ...Most cases of nocardiosis are seen in immunocompromised patients. Primary lymphocutaneous is a relatively uncommon presentation of this disease that may also occurs in normal hosts. Diagnosing this infection requires a high index of suspicion since cultures can take several days to exhibit growth. The microbiology laboratory must therefore be notified about cases in which this pathogen is suspected. We report four cases of primary lymphocutaneous norcardiosis. Of particular interest is the association of three of these cases with gardening.展开更多
Grove Mountains (GRV) 99018 is a new eucrite (0.23 g), consisting mainly of pyroxene (50.5 vol%) and plagioclase (37.2 vol%) with minor silica minerals (7.0 Vol%) and opaque minerals (5.2 vol%). It was intensely shock...Grove Mountains (GRV) 99018 is a new eucrite (0.23 g), consisting mainly of pyroxene (50.5 vol%) and plagioclase (37.2 vol%) with minor silica minerals (7.0 Vol%) and opaque minerals (5.2 vol%). It was intensely shocked, leading to partial melting, formation of abundant tiny inclusions in pyroxenes and plagioclase, and heavy brecciation. Exsolution of most pyroxenes (1-3μm in width of the lamellae), recrystallization of the shpck-induced melt pockets and veins (5-20μm in size), and homogeneous compositions of pyroxenes of various occurrences suggest the intense thermal metamorphism of GRV 99018 in the asteroidal body Vesta. This new eucrite will bring additional constraints on the chemical composition and multi-stage thermal and shock history of Vesta.展开更多
文摘In a Nature Physics report published in late September 2024[1],a team of scientists and engineers at Sandia National Laboratories(Albuquerque,NM,USA)described the results of a laboratory experiment showing that a nuclear blast could create a burst of X-rays powerful enough to change the path of a large asteroid that might one day be on a collision course with Earth.
基金supported by China’s first Asteroid exploration program and China National Space Administration(CNSA)was also funded by the National Natural Science Foundation of China (NSFC,Grant No.12373068)。
文摘The surface particle size and distribution characteristics of celestial bodies (e.g.,the Moon,asteroids,etc.) will affect the interpretation of hyperspectral remote sensing data and the implementation of sampling missions.Currently,the estimation of the surface particle sizes is mainly focusing on interpreting the thermal inertia with the infrared spectral data from ground-based or space telescopes,but this method show distinct errors compared with the imaging results of the orbiter.By analyzing some thermal infrared spectral data,a relationship between the particle sizes of the main rockforming minerals (e.g.pyroxene,feldspar,olivine) and the slopes of their thermal infrared spectrum was found.Based on this relationship,a preliminary model for estimating the grain sizes (~30–300μm) of lunar or S-type asteroids’surfaces which are silicate minerals dominated was established,and the correlation coefficients (R^(2)) for most of the rock-forming minerals were better than 90%.Six observational datasets of natural lunar and terrestrial samples are used to validate the model,and the results show a systematical overestimation of the ground-truth particle sizes,the potential causes are analyzed and an additional correction is used to eliminate the overestimation of the particle size prediction.These results are expected to provide guidance for interpretation of lunar and S-type asteroid surface sampling and spectral data.
基金supported by the National Key Research and Development Program of China(No.2019YFA0706500)。
文摘Flexible lander,composed of multiple nodes connected by flexible material,can reducethe bouncing and overturning during the asteroid landing.To satisfy the complex constraints inthe node cooperation of the flexible landing,an intelligent cooperative guidance method is pro-posed.The method consists of a double-layer cooperative guidance structure,a guidance parameterdetermination approach,and an action priority strategy.The double-layer contains a basic guid-ance used to satisfy the terminal state constraints,and a compensatory guidance used to satisfythe lander's attitude constraint.For the compensatory guidance,the parameters are determinedby multi-agent system,which are trained according to the performance index of flexible landing tra-jectories.The action priority strategy is used to reduce the detrimental effect of parameter inconsis-tency on the node cooperation.The simulation of flexible landing shows that the cooperativeguidance method is effective in improving the landing accuracy while satisfying the constraints.Meanwhile,the method is robust to the disturbance in the navigation and control.
文摘At the end of the Cretaceous period,66 million years ago,the 7−19 km diameter Chicxulub asteroid hit the Yucatan Peninsula in Mexico,triggering global catastrophic environmental changes and mass extinction.The contributions of this event towards changes in plate and plume geodynamics are not fully understood.Here we present a range of geological observations indicating that the impact marked a tectonic turning point in the behavior of mantle plume and plate motion in the Caribbean region and worldwide.At a regional scale,the impact coincides with the termination of seafloor spreading in the Caribbean Ridge.Shortly after the Cretaceous-Paleogene transition,magmatism associated with the Caribbean Large Igneous Province waned,and intensive Paleogene volcanism was initiated.These events happened synchronously with anomalously high mid-ocean ridge magmatism worldwide and an abrupt change in the relative motion of the South American and North American tectonic plates.The evidence for such abrupt changes in plate kinematics and plume behavior raises the possibility that the Chicxulub impact triggered a chain of effects that modified melt reservoirs,subducting plates,mantle flows,and lithospheric deformation.To explain how an asteroid impact could modify tectonic behavior,we discuss two end-member mechanisms:quasi-static and dynamic triggering mechanisms.We designed a numerical model to investigate the strain field and the relative plate motion before and after the impact.The model predicts an enhanced deformation associated with the impact,which surficially tapers off∼500 km from the crater.The impact modifies the subjacent mantle flow field,contributing to long-term mantle-driven dynamic changes.Additionally,deformation associated with seismic effects may have contributed to far-field effects and global changes.We conclude that large asteroid impacts,such as the Chicxulub collision,could trigger cascading effects sufficient to disrupt and significantly modify plate geodynamics.
基金funded by the National Science and Technology Major Project(2022ZD0117401)the National Defense Science and Technology Innovation Special Zone Project Foundation of China(grant No.19-163-21-TS-001-067-01)support was provided by the Chinese Academy of Sciences(CAS)“Light of West China”Program(No.2020-XBQNXZ-016 and No.2022-XBQNXZ-016).
文摘Near-Earth Asteroids posed a threat to human civilization,making their monitoring crucial.As the demand for asteroid detection technology increased,precise detection of these celestial bodies became an urgent task to understand their characteristics and assess potential impact risks.To improve asteroid detection accuracy and efficiency,we proposed an advanced image processing method and a deep learning network for automatic asteroid detection.Specifically,we aligned star clusters and overlaid images to exploit asteroid motion rates,transforming them into object-like trajectories and improving the signal-to-noise ratio.This approach created the Asteroid Trajectory Image Data set under various conditions.We modified CenterNet2 network to develop AstroCenterNet by integrating Multi-channel Histogram Truncation for feature enhancement,using the SimAM attention mechanism to expand contextual information and suppress noise,and refining Feature Pyramid Network to improve low-level feature detection.Our results demonstrated a detection accuracy of 98.4%,a recall of 97.6%,a mean Average Precision of 94.01%,a false alarm rate of 1.6%,and a processing speed of approximately 17.86 frames per second,indicating that our method achieves high precision and efficiency.
基金supported by the Special Funding Project for Space Debris and Near-Earth Asteroids Defense Research, China (No. KJSP2023020303)Beijing Municipal Science and Technology Commission, China (No. Z181100002918004)the Youth Innovation Promotion Association, Chinese Academy of Sciences (No. 2022146)
文摘Implementing the flyby to Near-Earth Asteroids (NEAs) with the potential impact risks to the Earth allows for obtaining detailed physical parameters, thereby supporting the high-precision orbit prediction and planetary defense strategy. Different from those conducted asteroid flyby missions, in the 12th China Trajectory Optimization Competition (CTOC-12), a NEAs flyby trajectory design problem using reusable probes that depart from a Lunar Distant Retrograde Orbit (DRO) station in the cislunar space was released. The objective was flyby to as many NEAs as possible using up to 20 probes within a total of 10 years. The ∑ team proposed a solution that can explore 47 NEAs using 11 probes, ranking the first in the competition. In this paper, the methods and results from the winning team are introduced, including mission analysis and preliminary design, and low-energy transfer trajectory optimization. In particular, a round-trip trajectory is divided into three phases: deep space transfer, indirect transfer between the Earth to DRO, and DRO phasing and rendezvous. With the combination of global optimization and local optimization algorithms, the required velocity increments to change the orbital planes are effectively reduced, thus increasing the number of the explored NEAs. The final solution of our team is presented and the results are compared with those of the top three teams. The competition demonstrates that the regularization of flyby missions from the cislunar space to explore NEAs with the potential impact risks to the Earth is the feasible and promising.
文摘Sent out at 1:31am GMT+8 on May 29 by a Long March-3B carrier rocket from the Xichang Satellite Launch Center in Sichuan province,China,Tianwen-2,the second mission of China’s Planetary Exploration Program,correctly entered the transfer trajectory toward an asteroid named 2016HO3 after flying for 18 minutes.Its solar wings unfolded properly,signaling a successful start,and primed for the next stage of its mission.
基金supports from the National Natural Science Foundation of China(NSFC,grant Nos.12203002 and 11973015)supports from the National Key Basic R&D Program of China via 2023YFA1608303 and the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB0550103)+6 种基金supports from the National Natural Science Foundation of China(NSFCgrant No.12373015)supports from the National Natural Science Foundation of China(NSFCgrant Nos.12120101003 and 12373010)National Key R&D Program of China(grant Nos.2023YFA1607800,2023YFA1607804,2022YFA1602902)Beijing Municipal Natural Science Foundation(grant No.1222028)Strategic Priority Research Program of the Chinese Academy of Science(grant Nos.XDB0550100 and XDB0550000).
文摘The SiTian project,with its vast field of view,will become an ideal platform for scientific research on asteroids.In this study,we develop a pipeline to analyze the photometry of asteroids and derive their periods from the data collected by the SiTian pathfinder project Mini-SiTian(MST).The pipeline is applied to the MST f02 region,an MST test region with a sky area of 2°.29×1°.53.Rotation periods of 22 asteroids are derived by the obtained light curve analysis.Among them,there are eight asteroids available in the Asteroid Lightcurve Photometry Database(ALCDEF),and six of them with more photometric points(>200)that have similar period parameters as the ones in ALCDEF.Additionally,the periods for 14 of these asteroids are newly obtained and are not listed in ALCDEF.This study demonstrates the feasibility of asteroid photometric research by the SiTian project.It shows that future observations from the SiTian project will provide even more photometry of asteroids,significantly increasing the number of available light curves.The potential vast photometric data on asteroids will help us to further understand the physics of asteroids,their material composition,and the formation and evolution of the solar system.
基金Funding for the telescope has been provided by CAS and the People’s Government of Yunnan Provincefunded by the Civil Aerospace pre-research project D020302+2 种基金National Natural Science Foundation of China (U12150009,12150009)the CAS Light of West China Programthe science research grants from the China Manned Space Project with NO.CMS-CSST-2021-B10
文摘The perihelion of long-period comets places them near the Sun so they may exhibit activity.Before 2013 LU28 reached its perihelion,we performed a continuous observation to detect possible activity.Using the Lijiang 2.4 m telescope with a Johnson R filter,we measured the brightness of 2013 LU28 from 2024 January 3 to April 13.The instrumental magnitudes were subsequently transformed into the Pan-STARRS r system.Due to the noticeable descending trend in the absolute magnitude,we verified the cometary activity and constrained some photometric properties of 2013 LU28.Consequently,the increased cross-sectional area had a rate of 42.8 km^(2)day^(−1),and the corresponding mass-loss rate was 2.64 kg s^(−1)with the assumption of a dust-particle size a=10 mm and the densityρ=400 kg m^(−3).We estimated the nucleus radius as 0.11■r_(n)■0.21 km for CO sublimation and 0.20■r_(n)■0.71 km for CO_(2)sublimation and the grain size of 2013 LU28 was ac;117.95μm for CO and ac■7.57μm for CO_(2).The long-term observations provided in this paper will offer significant value for investigating the mechanisms driving the activity of 2013 LU28.
基金supported by the Science and Technology Development Fund of Macao (FDCT)(grant 002/2024/SKL)。
文摘Magnetite-ilmenite pairs in meteorites serve as reliable thermometers and oxygen fugacity (fO_(2)) indicators for constraining both nebular conditions and thermal metamorphic histories.While CK and CV chondrites exhibit nearly identical petrological characteristics and oxygen isotope compositions,our analysis of NWA 16813 reveals it records the highest fO_(2)(log fO_(2)=-20.51 (589.34°C)-log fO_(2)=-14.21 (608.63°C))yet measured among these meteorites.This finding provides critical evidence that CK and CV chondrites experienced fundamentally different redox conditions during their formation.The fO_(2)data from NWA16813,combined with its distinct petrological and mineralogical features,strongly suggest that CK and CV chondrites originated from chemically separate reservoirs in the protoplanetary disk despite their apparen similarities.
基金financial support from the Science Research Foundation of Yunnan Education Department of China(grant 2020J0649)the Natural Science Foundation of Yunnan Province(grant 202101AU070010)the financial support from the Hundred Talents Program of Yuxi(grant 2019-003)。
文摘The shapes and rotation states(periods and pole orientations)of main-belt asteroids are important for understanding their formation and evolution.In order to obtain sufficient photometric data covering different apparitions for asteroid(81)Terpsichore,ground-based photometric observations in 2020 and 2021 were carried out.By combining published and newly obtained photometric data,we calculated the shape and spin parameters for(81)Terpsichore using the convex inversion method.With this method,we have derived a best fitted pole orientation—(22.2±_(3.1)^(3.3°),17.5±_(5.5)^(10.8°))with a spin period of 10.94±_(0.01)^(0.01)h.Based on the derived convex shape of(81)Terpsichore,we have fitted the H,G+1,G_(2)phase function using the calibrated TESS data and Gaia data after accounting for the lightcurve amplitude correction.As a result,we have derived its absolute magnitude H=8.68±_(0.19)^(0.22)mag with corresponding phase function parameters G_(1)=0.82±_(0.10)^(0.09)and G_(2)=0.02±_(0.02)^(0.03).
基金supported by Basic Research Project of China(grant No:JCKY2020110C096)the National Key R&D Program of China (grant No:2020YFC2201202)。
文摘As the second of Earth's Trojan asteroids, 2020 XL_(5) is worthy of rendezvous and even sample return missions in many aspects. In this paper, a rendezvous mission to Earth's second Trojan asteroid 2020 XL_(5) is proposed.However, due to its high inclination and large eccentricity, direct impulsive transfer requires large amounts of fuel consumption. To address this challenge, we explore the benefits of electric propulsion and multi-gravity assist techniques for interplanetary missions. These two techniques are integrated in this mission design. The design of a low-thrust gravity-assist(LTGA) trajectory in multi-body dynamics is thoroughly investigated,which is a complex process. A comprehensive framework including three steps is presented here for optimization of LTGA trajectories in multi-body dynamics. The rendezvous mission to 2020 XL_(5) is designed with this three-step approach. The most effective transfer sequence among the outcomes involves Earth–Venus–Earth–Venus-2020 XL_(5). Numerical results indicate that the combination of electric propulsion and multi-gravity assists can greatly reduce the fuel consumption, with fuel consumption of 9.03%, making it a highly favorable choice for this rendezvous mission.
基金supported by the Characteristic innovation project of Guangdong Provincial Department of Education(No.2023KTSCX195)Scientific Computing Research Innovation Team of Guangdong Province(No.2021KCXTD052)+2 种基金Guangdong Key Construction Discipline Research Capacity Enhancement Project(No.2022ZD JS049)Technology Planning Project of Shaoguan(No.230330108034184)Science and Technology Development Fund,Macao SAR(No.0096/2022/A)。
文摘Determining asteroid properties provides valuable physical insights but inverting them from photometric lightcurves remains computationally intensive.This paper presents a new approach that combines a simplified Cellinoid shape model with the Parallel Differential Evolution(PDE)algorithm to accelerate inversion.The PDE algorithm is more efficient than the Differential Evolution algorithm,achieving an extraordinary speedup of 37.983 with 64 workers on multicore CPUs.The PDE algorithm accurately derives period and pole values from simulated data.The analysis of real asteroid lightcurves validates the method’s reliability:in comparison with results published elsewhere,the PDE algorithm accurately recovers the rotational periods and,given adequate viewing geometries,closely matches the pole orientations.The PDE approach converges to solutions within 20,000 iterations and under one hour,demonstrating its potential for large-scale data analysis.This work provides a promising new tool for unveiling asteroid physical properties by overcoming key computational bottlenecks.
基金supported by the Strategic Priority Research Program on Space Science,the Chinese Academy of Sciences(No.XDA1502030505)。
文摘In history,the Earth has encountered frequent and massive impacts.Until today,it is still a collided target for Potentially Hazardous Objects(PHOs),gradually making planetary defense a concerned and important research topic in the field of aerospace science.Against this background,this work clarifies and discusses some important scientific issues and various critical technologies of planetary defense.First,the current status of planetary defense research is summarized.Subsequently,the classification and characteristics of PHOs are introduced,focusing on their potential impact on planetary defense and related scientific research issues.For the purpose of protecting the Earth and maintaining space safety,the monitoring and characterization,deflection,and mitigation of PHOs have basically occupied all the attention of planetary defense researchers.Therefore,the critical technologies in planetary defense are discussed from these three aspects,and are also compared and analyzed in depth.Based on the current research progress in planetary defense,the challenges for planetary defense are discussed,and future development directions are also analyzed.Finally,a summary of the entire study is provided.
文摘The characteristics of asteroids are vital parameters for planning asteroid exploration missions.These characteristics have been explored in close range for some typical asteroids,and are summarized in the article.This allows estimates of the characteristics of asteroid 2016HO_(3),the target of the first Chinese asteroid exploration mission,Tianwen 2.We obtain 80 characteristic parameters in 9 categories and analyze their impacts on the mission.By comparing three close-range exploration modes,we provide advantages and disadvantages of each,and propose suitable methods for the exploration of 2016HO_(3).Owing to the weak gravity and small size of 2016HO_(3),a combination of multiple hovering positions and active orbiting is recommended for scientific exploration.
文摘A compilation of many different kinds of natural scientific investigations and their interrelations as well as their collective interpretation are necessary to understand past, presence and future of the Earth’s system adequately. This has been tried with somehow surprising results in this paper. Milky Way related cycles on Earth of 150 Myr duration as observed for the Phanerozoic Eon are obviously not dominant in the Proterozoic Eon. Only a very weak galactic signal due to periodic occurrences of phosphorous may be present that has entered the Earth from exploding stars. The Phanerozoic can be defined as an eon with very sensitive geophysical, geological, meteorological and biological reactions. The accelerated reactions from a 400 Myr to a 300 Myr cycle of mineral ages and continental tectonics include a generally high surface temperature with glacial interruptions, high oxygen and ozone values in the atmosphere, increase of the strength of the magnetic field and the rise of the asteroid impact rate witness those sensitives. It cannot be excluded after analyzing all related data that 1) Asteroid impacts stabilized and strengthened the Earth’s magnetic field, 2) apparently the acceleration of geodynamic processes on Earth after weakening of the dynamics of Earth’s core (geodynamo) is Milky Way supported, 3) the life spending biologically produced oxygen and its ozone derivative can influence Earth’s climate significantly, and 4) somehow time coordinated events like asteroid impacts, Earth’s core dynamics, nearby exploding stars, solar system pathway through dusty spiral arms, plate tectonics, a speculative companion of the Sun (or something else) and oxygen production via photosynthesis were essential ingredients for the remarkable success of life on Earth.
文摘BACKGROUND Systemic lupus erythematosus(SLE)patients are extremely susceptible to opportunistic infections due to glucocorticoid and immunosuppressive treatments,which often occur in the respiratory system,the urinary system and the skin.However,multiple cerebral infections are rarely reported and their treatment is not standardized,especially when induced by a rare pathogen.CASE SUMMARY A 46-year-old woman was treated with glucocorticoid and immunosuppressant for SLE involving the hematologic system and kidneys(class IV-G lupus nephritis)for more than one year.She was admitted to hospital due to headache and fever,and was diagnosed with multiple cerebral abscesses.Brain enhanced magnetic resonance imaging showed multiple nodular abnormal signals in both frontal lobes,left parietal and temporal lobes,left masseteric space(left temporalis and masseter region).The initial surgical plan was only to remove the large abscesses in the left parietal lobe and right frontal lobe.After surgery,based on the drug susceptibility test results(a rare pathogen Nocardia asteroides was found)and taking into consideration the patient’s renal dysfunction,a multi-antibiotic regimen was selected for the treatment.The immunosuppressant mycophenolate mofetil was discontinued on admission and the dose of prednisone was reduced from 20 mg/d to 10 mg/d.Re-examination at 3 mo post-surgery showed that the intracranial lesions were reduced,the edema around the lesions was absorbed and dissipated,and her neurological symptoms had disappeared.The patient had no headaches or other neurological symptoms and lupus nephritis was stable during the 2-year follow-up period.CONCLUSION In this report,we provide reasonable indications for immunosuppression,anti-infective therapy and individualized surgery for an SLE patient complicated with multiple cerebral abscesses caused by a rare pathogen,which may help improve the diagnosis and treatment of similar cases.
文摘Most cases of nocardiosis are seen in immunocompromised patients. Primary lymphocutaneous is a relatively uncommon presentation of this disease that may also occurs in normal hosts. Diagnosing this infection requires a high index of suspicion since cultures can take several days to exhibit growth. The microbiology laboratory must therefore be notified about cases in which this pathogen is suspected. We report four cases of primary lymphocutaneous norcardiosis. Of particular interest is the association of three of these cases with gardening.
基金We are grateful to Drs Guan Yunbin and Xu Ping for their assistance in laboratories This study is supported by the National Natural Science Foundation of China(Grant No.40232026)the pilot project of knowledge-innovation program of the Chinese Academy of Sciences(Grant No.KZCX3-SW-l23).
文摘Grove Mountains (GRV) 99018 is a new eucrite (0.23 g), consisting mainly of pyroxene (50.5 vol%) and plagioclase (37.2 vol%) with minor silica minerals (7.0 Vol%) and opaque minerals (5.2 vol%). It was intensely shocked, leading to partial melting, formation of abundant tiny inclusions in pyroxenes and plagioclase, and heavy brecciation. Exsolution of most pyroxenes (1-3μm in width of the lamellae), recrystallization of the shpck-induced melt pockets and veins (5-20μm in size), and homogeneous compositions of pyroxenes of various occurrences suggest the intense thermal metamorphism of GRV 99018 in the asteroidal body Vesta. This new eucrite will bring additional constraints on the chemical composition and multi-stage thermal and shock history of Vesta.
