Comets are small celestial bodies orbiting around the Sun.They are remnants left over from the formation of the solar system;their interiors store original material of the planetary disk within the solar system.They a...Comets are small celestial bodies orbiting around the Sun.They are remnants left over from the formation of the solar system;their interiors store original material of the planetary disk within the solar system.They are thus"fossils"for studying the early solar system.According to their orbital periods,comets are classified as long-period comets(orbital period P>200 years)and short-period comets(P<200 years).Long-period comets originate from the Oort Cloud.Compared to short-period comets,they enter the inner solar system less frequently and contain more primitive materials.Studying long-period comets helps us understand the origin of the solar system and reveals characteristics of the Oort Cloud.This paper begins with a summary of our extensive survey of the literature regarding methods of observing comets and foci of comet studies.We introduce systematically the main parameters currently used to assess the activity of long-period comets,including gas production rate,dust production rate,dust properties,morphological characteristics,etc.Subsequently,we discuss in depth the activity mechanisms of long-period comets,covering not only the water ice sublimation-driven mechanism(similar to that of short-period comets)but also various mechanisms that may dominate the activity of long-period comets in the low-temperature environment at the aphelion.These mechanisms include the sublimation of CO or CO_(2) gas ice,the polymerization reaction of cyanides,the crystallization of amorphous water ice,the annealing process of amorphous water ice,the thermal decomposition effect,and the electrostatic supercharge phenomenon.We then summarize the evolving activity of long-period comets as they travel from the Oort Cloud to the vicinity of their perihelions.We analyze unique properties of long-period comets,including such special phenomena as changes in dust color,coma structure,and tail structure.Finally,we summarize currently unresolved scientific questions,and then the entire paper.展开更多
In this work,we report observations of three comets:38P/Stephan-Oterma,64P/Swift-Gehrels,and C/2017 M4(ATLAS),conducted with the Nanshan one-meter wide-field telescope in 2018 August and November,and 2019January.We ex...In this work,we report observations of three comets:38P/Stephan-Oterma,64P/Swift-Gehrels,and C/2017 M4(ATLAS),conducted with the Nanshan one-meter wide-field telescope in 2018 August and November,and 2019January.We extracted morphological features through image enhancement techniques and calculated the dust activity parameter,Afρ,along with dust mass loss rates and coma color indices using broadband photometric data.Our morphological analysis uncovered a spectrum of dust characteristics among the observed comets,ranging from a significant twisted structure in comet 38P/Stephan-Oterma’s coma to the regular coma envelope surrounding comet 64P/Swift-Gehrels.The Afρvalues varied between 148.8±0.3 cm for 64P/Swift-Gehrels and1118.5±6.2 cm for C/2017 M4(ATLAS)(measured within a reference aperture radius ofρ=6″),indicating a range from moderate to high activity levels.Dust mass loss rates were estimated from 328.1 kg s^(-1)for comet 64P/Swift-Gehrels to 1395.5 kg s^(-1)for comet C/2017 M4(ATLAS).The color indices of comets 38P/Stephan-Oterma and C/2017 M4(ATLAS)closely resemble the average colors of active short-period comets and active longperiod comets,respectively.In contrast,64P/Swift-Gehrels exhibits a significantly bluer hue than typical Jupiter family comets.展开更多
Objective A new technique of transthoracic lung ultrasonography(TLS) has emerged and demonstrated promising results in acute heart failure diagnosis at an early stage. However, the diagnostic value of ultrasound lung ...Objective A new technique of transthoracic lung ultrasonography(TLS) has emerged and demonstrated promising results in acute heart failure diagnosis at an early stage. However, the diagnostic value of ultrasound lung comets(ULCs) for acute heart failure(AHF) performed in busy emergency department(ED) is uncertain. The present meta-analysis aimed to assess the diagnostic efficiency of ULCs in AHF. Methods We conducted a search on online journal databases to collect the data on TLS performed for diagnosing AHF published up to the end of July 2017. The sensitivity, specificity, positive likelihood ratio(PLR), negative likelihood ratio(NLR), and summary receiver operating characteristic(SROC) curve were calculated. The post-test probability of AHF was calculated by using Bayes analysis. Results We enrolled a total of 15 studies involving 3,309 patients. The value of sensitivity, specificity, PLR, NLR, DOR, area under the SROC curve, and Q* index was 85%, 91%, 8.94, 0.14, 67.24, 0.9587, and 0.9026, respectively. We detected significant heterogeneity among included studies, and therefore, all these results were analyzed under the random-effect model. We also explored possible sources of heterogeneity among the studies by using meta-regression analysis. Results suggest that the time interval between patient’s admission to bedside TLS examination was closely related to TLS accuracy. Conclusion This meta-analysis demonstrated that detecting ULCs is a convenient bedside tool and has high accuracy for early AHF diagnosis in ED. TLS could be recommended to be applied for early diagnosis of AHF in ED.展开更多
We used the Five-hundred-meter Aperture Spherical radio Telescope(FAST)to search for the molecular emissions in the L-band between 1.0 and 1.5 GHz toward four comets,C/2020 F3(NEOWISE),C/2020 R4(ATLAS),C/2021 A1(Leona...We used the Five-hundred-meter Aperture Spherical radio Telescope(FAST)to search for the molecular emissions in the L-band between 1.0 and 1.5 GHz toward four comets,C/2020 F3(NEOWISE),C/2020 R4(ATLAS),C/2021 A1(Leonard),and 67P/Churyumov-Gerasimenko during or after their perihelion passages.Thousands of molecular transition lines fall in this low-frequency range,many attributed to complex organic or prebiotic molecules.We conducted a blind search for the possible molecular lines in this frequency range in those comets and could not identify clear signals of molecular emissions in the data.Although several molecules have been detected at high frequencies of greater than100 GHz in comets,our results confirm that it is challenging to detect molecular transitions in the L-band frequency ranges.The non-detection of L-band molecular lines in the cometary environment could rule out the possibility of unusually strong lines,which could be caused by the masers or non-LTE effects.Although the line strengths are predicted to be weak,for FAST,using the ultra-wide bandwidth receiver and improving the radio frequency interference environments would enhance the detectability of those molecular transitions at low frequencies in the future.展开更多
We present simulation results on evolution development of orbital motion of short-period comets with the revolution period not exceeding 6-7 years, namely comets 21P/Giacobini-Zinner, 26P/Grigg- Skjellerup and 7P/Pons...We present simulation results on evolution development of orbital motion of short-period comets with the revolution period not exceeding 6-7 years, namely comets 21P/Giacobini-Zinner, 26P/Grigg- Skjellerup and 7P/Pons-Winnecke. The calculations cover the range from the date of the object＇s discovery to 2100. Variations in the objects＇ orbital elements under the action of gravity disturbances, taking Earth＇s gravitational potential into account when the small body approaches, are analyzed. Corrected dates of peri- helion passages can be used for scheduling observations.展开更多
SUISEI is a suite of computational tools that has been developed over the past three decades and successfully applied to comets;including ComChem, a global, multi-fluid gas dynamics simulation with detailed chemical k...SUISEI is a suite of computational tools that has been developed over the past three decades and successfully applied to comets;including ComChem, a global, multi-fluid gas dynamics simulation with detailed chemical kinetics of the cometary coma;ComDust, a model of comet dust evolution and interaction with gas;and ComNuc, a 3-D simulation of gas and heat flow within the comet nucleus porous subsurface layers. The combination of these tools have resulted in an improved knowledge of chemical species in the comet’s coma and their relationship to native molecules in the nucleus ices by analyzing space- and ground-based observations and in situ measurements from spacecraft missions. A review of SUISEI is presented and applications are made to two cases: chemical recycling of HCN in comets and the physical conditions of the near-Sun object, 3200 Phaethon.展开更多
Since the concept of Nongravitational Force (hereafter NF) was first proposed a century and a half ago, different models of it have been suggested and being modified. Its effect on the orbital motions of comets has be...Since the concept of Nongravitational Force (hereafter NF) was first proposed a century and a half ago, different models of it have been suggested and being modified. Its effect on the orbital motions of comets has been studied. Especially, some researchers have attempted to draw some inclues of the physical nature of the cometary nucleus from the NF parameters. In this paper, we try to give a concise review about the different models of NF and their effects on orbit computation. And then, we will try to detect whether there is nongravitational effect on Comet Hale-Bopp’s orbital motion using Style II NF model.展开更多
Although people have studied comets for a long time and used spacecraft to detect comets in a short distance,the formation time and causes of comets are still unresolved.Therefore,according to the formation and evolut...Although people have studied comets for a long time and used spacecraft to detect comets in a short distance,the formation time and causes of comets are still unresolved.Therefore,according to the formation and evolution law of planets and the dynamic mechanism,the author thoroughly revealed the formation and evolution of comets:A powerful storm cyclone on Neptune,such as the Great Dark Spot,can involve a large number of clouds.These clouds are gradually cooled and compressed in the process of rapidly sinking along the spiral path,and then condense into huge water ice crystals at the bottom of the cyclone;When such a crystal falls into a deep hole filled with liquid hydrogen,it is easy to collide violently with the boulders in the hole,and instantly ignite the liquid hydrogen in the hole.Under the strong push of high-pressure gas,some fragments of the ice crystal can quickly reach a very high initial speed.Especially when the jet direction of the Great Dark Spot is consistent with the direction of Neptune’s revolution speed,such fragments can quickly reach Neptune’s escape speed of 23.56 km/s.Therefore,the fragments can break away from Neptune and enter an elliptical orbit around the sun,becoming a comet.Similarly,when the metal hydrogen at the bottom of a Great Red Spot on Jupiter explodes in a series,the fragments ejected from the Great Red Spot can reach the escape speed of Jupiter of 60 km/s,therefore,such fragments can break away from Jupiter and enter the elliptical orbit around the sun to become comets.Many of these comets can become asteroids in the asteroid belt,which is the formation principle of the asteroid belt.展开更多
The historical records of astronomical phenomena may play a significant role in comet identification.Getting an accurate result is based on many factors,of which the calculation of orbital elements is the most importa...The historical records of astronomical phenomena may play a significant role in comet identification.Getting an accurate result is based on many factors,of which the calculation of orbital elements is the most important.This paper presents a "Cross Reference" method in which the perturbation of Jupiter is the only considered factor used to attempt an efficient way of comet identification with ancient Chinese historical records.In this method,the records before and after the calculated result from orbital determination within the error range are compared with the historical records to find the correlated perihelion time,and then,with five other orbital elements at the perihelion time,the ephemeris is calculated.If the calculated ephemeris matches the historical records,it is concluded that the comet determined by orbital calculation is the same as the one recorded in history.With this method,three comets with four historical records have already been found.展开更多
If you happen to gaze up in the sky at just the right time in the year 2061,you might get to see one of the most famous comets of all.It's called Halley's Comet,and people get a chance to see it every 76years ...If you happen to gaze up in the sky at just the right time in the year 2061,you might get to see one of the most famous comets of all.It's called Halley's Comet,and people get a chance to see it every 76years when the comets orbit brings it close to the Earth.展开更多
基金supported by the Operation,Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments,budgeted from the Ministry of Finance of China(MOF)and administrated by the Chinese Academy of Sciences(CAS)the National Natural Science Foundation of China(grant Nos.12173093)science research grants from the China Manned Space Project with No.CMS-CSST-2021-B08.
文摘Comets are small celestial bodies orbiting around the Sun.They are remnants left over from the formation of the solar system;their interiors store original material of the planetary disk within the solar system.They are thus"fossils"for studying the early solar system.According to their orbital periods,comets are classified as long-period comets(orbital period P>200 years)and short-period comets(P<200 years).Long-period comets originate from the Oort Cloud.Compared to short-period comets,they enter the inner solar system less frequently and contain more primitive materials.Studying long-period comets helps us understand the origin of the solar system and reveals characteristics of the Oort Cloud.This paper begins with a summary of our extensive survey of the literature regarding methods of observing comets and foci of comet studies.We introduce systematically the main parameters currently used to assess the activity of long-period comets,including gas production rate,dust production rate,dust properties,morphological characteristics,etc.Subsequently,we discuss in depth the activity mechanisms of long-period comets,covering not only the water ice sublimation-driven mechanism(similar to that of short-period comets)but also various mechanisms that may dominate the activity of long-period comets in the low-temperature environment at the aphelion.These mechanisms include the sublimation of CO or CO_(2) gas ice,the polymerization reaction of cyanides,the crystallization of amorphous water ice,the annealing process of amorphous water ice,the thermal decomposition effect,and the electrostatic supercharge phenomenon.We then summarize the evolving activity of long-period comets as they travel from the Oort Cloud to the vicinity of their perihelions.We analyze unique properties of long-period comets,including such special phenomena as changes in dust color,coma structure,and tail structure.Finally,we summarize currently unresolved scientific questions,and then the entire paper.
基金supported by the Natural Science Foundation of Xinjiang Uygur Autonomous Region of China(grant No.2021D01B112)Tianshan Talent Training Program through the grant 2023TSYCCX0101。
文摘In this work,we report observations of three comets:38P/Stephan-Oterma,64P/Swift-Gehrels,and C/2017 M4(ATLAS),conducted with the Nanshan one-meter wide-field telescope in 2018 August and November,and 2019January.We extracted morphological features through image enhancement techniques and calculated the dust activity parameter,Afρ,along with dust mass loss rates and coma color indices using broadband photometric data.Our morphological analysis uncovered a spectrum of dust characteristics among the observed comets,ranging from a significant twisted structure in comet 38P/Stephan-Oterma’s coma to the regular coma envelope surrounding comet 64P/Swift-Gehrels.The Afρvalues varied between 148.8±0.3 cm for 64P/Swift-Gehrels and1118.5±6.2 cm for C/2017 M4(ATLAS)(measured within a reference aperture radius ofρ=6″),indicating a range from moderate to high activity levels.Dust mass loss rates were estimated from 328.1 kg s^(-1)for comet 64P/Swift-Gehrels to 1395.5 kg s^(-1)for comet C/2017 M4(ATLAS).The color indices of comets 38P/Stephan-Oterma and C/2017 M4(ATLAS)closely resemble the average colors of active short-period comets and active longperiod comets,respectively.In contrast,64P/Swift-Gehrels exhibits a significantly bluer hue than typical Jupiter family comets.
基金supported by the capital characteristic clinic project of China [Z151100004015071]National Natural Science Foundation of China [51573211]ruiyi emergency medical research fund of China [R2017013]
文摘Objective A new technique of transthoracic lung ultrasonography(TLS) has emerged and demonstrated promising results in acute heart failure diagnosis at an early stage. However, the diagnostic value of ultrasound lung comets(ULCs) for acute heart failure(AHF) performed in busy emergency department(ED) is uncertain. The present meta-analysis aimed to assess the diagnostic efficiency of ULCs in AHF. Methods We conducted a search on online journal databases to collect the data on TLS performed for diagnosing AHF published up to the end of July 2017. The sensitivity, specificity, positive likelihood ratio(PLR), negative likelihood ratio(NLR), and summary receiver operating characteristic(SROC) curve were calculated. The post-test probability of AHF was calculated by using Bayes analysis. Results We enrolled a total of 15 studies involving 3,309 patients. The value of sensitivity, specificity, PLR, NLR, DOR, area under the SROC curve, and Q* index was 85%, 91%, 8.94, 0.14, 67.24, 0.9587, and 0.9026, respectively. We detected significant heterogeneity among included studies, and therefore, all these results were analyzed under the random-effect model. We also explored possible sources of heterogeneity among the studies by using meta-regression analysis. Results suggest that the time interval between patient’s admission to bedside TLS examination was closely related to TLS accuracy. Conclusion This meta-analysis demonstrated that detecting ULCs is a convenient bedside tool and has high accuracy for early AHF diagnosis in ED. TLS could be recommended to be applied for early diagnosis of AHF in ED.
基金supported by a grant from the National Natural Science Foundation of China(NSFC)No.11988101by the NSFC grant Nos.11703047,11773041,U2031119,12173052,12173053,12373032,and 11963002+6 种基金support from the China Postdoctoral Science Foundation grant No.2023M733271the Foundation of Education Bureau of Guizhou Province,China(grant No.KY(2020)003)supported by the International Partnership Program of the Chinese Academy of Sciences,program No.114A11KYSB20210010the Youth Innovation Promotion Association of the Chinese Academy of Sciences(ID Nos.2023064,2018075,and Y2022027)the support from the National Key R&D Program of China grant Nos.2022YFC2205202 and 2020SKA0120100supported by the CAS“Light of West China”Programthe support by the NSFC grant No.12373026。
文摘We used the Five-hundred-meter Aperture Spherical radio Telescope(FAST)to search for the molecular emissions in the L-band between 1.0 and 1.5 GHz toward four comets,C/2020 F3(NEOWISE),C/2020 R4(ATLAS),C/2021 A1(Leonard),and 67P/Churyumov-Gerasimenko during or after their perihelion passages.Thousands of molecular transition lines fall in this low-frequency range,many attributed to complex organic or prebiotic molecules.We conducted a blind search for the possible molecular lines in this frequency range in those comets and could not identify clear signals of molecular emissions in the data.Although several molecules have been detected at high frequencies of greater than100 GHz in comets,our results confirm that it is challenging to detect molecular transitions in the L-band frequency ranges.The non-detection of L-band molecular lines in the cometary environment could rule out the possibility of unusually strong lines,which could be caused by the masers or non-LTE effects.Although the line strengths are predicted to be weak,for FAST,using the ultra-wide bandwidth receiver and improving the radio frequency interference environments would enhance the detectability of those molecular transitions at low frequencies in the future.
文摘We present simulation results on evolution development of orbital motion of short-period comets with the revolution period not exceeding 6-7 years, namely comets 21P/Giacobini-Zinner, 26P/Grigg- Skjellerup and 7P/Pons-Winnecke. The calculations cover the range from the date of the object＇s discovery to 2100. Variations in the objects＇ orbital elements under the action of gravity disturbances, taking Earth＇s gravitational potential into account when the small body approaches, are analyzed. Corrected dates of peri- helion passages can be used for scheduling observations.
文摘SUISEI is a suite of computational tools that has been developed over the past three decades and successfully applied to comets;including ComChem, a global, multi-fluid gas dynamics simulation with detailed chemical kinetics of the cometary coma;ComDust, a model of comet dust evolution and interaction with gas;and ComNuc, a 3-D simulation of gas and heat flow within the comet nucleus porous subsurface layers. The combination of these tools have resulted in an improved knowledge of chemical species in the comet’s coma and their relationship to native molecules in the nucleus ices by analyzing space- and ground-based observations and in situ measurements from spacecraft missions. A review of SUISEI is presented and applications are made to two cases: chemical recycling of HCN in comets and the physical conditions of the near-Sun object, 3200 Phaethon.
文摘Since the concept of Nongravitational Force (hereafter NF) was first proposed a century and a half ago, different models of it have been suggested and being modified. Its effect on the orbital motions of comets has been studied. Especially, some researchers have attempted to draw some inclues of the physical nature of the cometary nucleus from the NF parameters. In this paper, we try to give a concise review about the different models of NF and their effects on orbit computation. And then, we will try to detect whether there is nongravitational effect on Comet Hale-Bopp’s orbital motion using Style II NF model.
文摘Although people have studied comets for a long time and used spacecraft to detect comets in a short distance,the formation time and causes of comets are still unresolved.Therefore,according to the formation and evolution law of planets and the dynamic mechanism,the author thoroughly revealed the formation and evolution of comets:A powerful storm cyclone on Neptune,such as the Great Dark Spot,can involve a large number of clouds.These clouds are gradually cooled and compressed in the process of rapidly sinking along the spiral path,and then condense into huge water ice crystals at the bottom of the cyclone;When such a crystal falls into a deep hole filled with liquid hydrogen,it is easy to collide violently with the boulders in the hole,and instantly ignite the liquid hydrogen in the hole.Under the strong push of high-pressure gas,some fragments of the ice crystal can quickly reach a very high initial speed.Especially when the jet direction of the Great Dark Spot is consistent with the direction of Neptune’s revolution speed,such fragments can quickly reach Neptune’s escape speed of 23.56 km/s.Therefore,the fragments can break away from Neptune and enter an elliptical orbit around the sun,becoming a comet.Similarly,when the metal hydrogen at the bottom of a Great Red Spot on Jupiter explodes in a series,the fragments ejected from the Great Red Spot can reach the escape speed of Jupiter of 60 km/s,therefore,such fragments can break away from Jupiter and enter the elliptical orbit around the sun to become comets.Many of these comets can become asteroids in the asteroid belt,which is the formation principle of the asteroid belt.
基金supported by theNational Natural Science Foundation of China (Grant No.10821061)the National Basic Research Program of China (Grant No.2007CB815103)
文摘The historical records of astronomical phenomena may play a significant role in comet identification.Getting an accurate result is based on many factors,of which the calculation of orbital elements is the most important.This paper presents a "Cross Reference" method in which the perturbation of Jupiter is the only considered factor used to attempt an efficient way of comet identification with ancient Chinese historical records.In this method,the records before and after the calculated result from orbital determination within the error range are compared with the historical records to find the correlated perihelion time,and then,with five other orbital elements at the perihelion time,the ephemeris is calculated.If the calculated ephemeris matches the historical records,it is concluded that the comet determined by orbital calculation is the same as the one recorded in history.With this method,three comets with four historical records have already been found.
文摘If you happen to gaze up in the sky at just the right time in the year 2061,you might get to see one of the most famous comets of all.It's called Halley's Comet,and people get a chance to see it every 76years when the comets orbit brings it close to the Earth.
