We describe and analyze observations of mutual events of Galilean satellites made at the Yunnan Observatory in February 2003 from CCD imaging for the first time in China. Astrometric positions were deduced from these ...We describe and analyze observations of mutual events of Galilean satellites made at the Yunnan Observatory in February 2003 from CCD imaging for the first time in China. Astrometric positions were deduced from these photometric observations by modelling the relative motion and the photometry of the involved satellites during each event.展开更多
The relationship between the k<SUB>2</SUB>/Q of the Galilean satellites and the k<SUB>2J</SUB>/Q<SUB>J</SUB> of Jupiter is derived from energy and momentum considerations. Calculati...The relationship between the k<SUB>2</SUB>/Q of the Galilean satellites and the k<SUB>2J</SUB>/Q<SUB>J</SUB> of Jupiter is derived from energy and momentum considerations. Calculations suggest that the Galilean satellites can be divided into two classes according to their Q values: Io and Ganymede have values between 10 and 50, while Europa and Callisto have values ranging from 200 to 700. The tidal contributions of the Galilean satellites to Jupiter's rotation are estimated. The main deceleration of Jupiter, which is about 99.04% of the total, comes from Io.展开更多
The nearby bright M-dwarf star L 98–59 has three terrestrial-sized planets.One challenge remaining in characterizing atmospheres around such planets is that it is not known a priori whether they possess any atmospher...The nearby bright M-dwarf star L 98–59 has three terrestrial-sized planets.One challenge remaining in characterizing atmospheres around such planets is that it is not known a priori whether they possess any atmospheres.Here we report on study of the atmospheres of L 98–59 c and L 98–59 d using near-infrared spectral data from the G141 grism of Hubble Space Telescope(HST)/Wide Field Camera 3.We can reject the hypothesis of a clear atmosphere dominated by hydrogen and helium at a confidence level of ~3σ for both planets.Thus they could have a primary hydrogen-dominated atmosphere with an opaque cloud layer,or could have lost their primary hydrogen-dominated atmosphere and re-established a secondary thin atmosphere,or have no atmosphere at all.We cannot distinguish between these scenarios for the two planets using the current HST data.Future observations with the James Webb Space Telescope would be capable of confirming the existence of atmospheres around L 98–59 c and d and determining their compositions.展开更多
A prominent observation of the solar system is that the mass and gas content of Jovian planets decrease outward with orbital radius, except that, in terms of these properties, Neptune is almost the same as Uranus. In ...A prominent observation of the solar system is that the mass and gas content of Jovian planets decrease outward with orbital radius, except that, in terms of these properties, Neptune is almost the same as Uranus. In previous studies, the solar nebula was assumed to preexist and the formation process of the solar nebula was not considered. It was therefore assumed that planet formation at different radii started at the same time in the solar nebula. We show that planet formation at different radii does not start at the same time and is delayed at large radii. We suggest that this delay might be one of the factors that causes the outward decrease in the masses of Jovian planets. The nebula starts to form from its inner part because of the inside-out collapse of its progenitorial molecular cloud core. The nebula then expands outward due to viscosity. Material first reaches a small radius and then reaches a larger radius, so planet formation is delayed at the large radius. The later the material reaches a planet＇s location, the less time it has to gain mass and gas content. Hence, the delay tends to cause the outward decrease in mass and gas content of Jovian planets. Our nebula model shows that the material reaches Jupiter, Saturn, Uranus and Neptune at t = 0.40, 0.57, 1.50 and 6.29 × 10^6 yr, respectively. We discuss the effects of time delay on the masses of Jovian planets in the framework of the core accretion model of planet formation. Saturn＇s formation is not delayed by much time relative to Jupiter so that they both reach the rapid gas accretion phase and become gas giants. However, the delay in formation of Uranus and Neptune is long and might be one of the factors that cause them not to reach the rapid gas accretion phase before the gas nebula is dispersed. Saturn has less time to go through the rapid gas accretion, so Saturn＇s mass and gas content are significantly less than those of Jupiter.展开更多
Mars is the only extraterrestrial body which could host primitive lifeforms and also has the potential to host a human base in the near future. Towards fulfilling these objectives, several remote sensing missions and ...Mars is the only extraterrestrial body which could host primitive lifeforms and also has the potential to host a human base in the near future. Towards fulfilling these objectives, several remote sensing missions and rover based missions have been sent to Mars. Still, confirmation of existing or extinct life on this planet in any form has not been achieved and possibly human missions at selected sites in the future are the key to addressing this problem. Here, we have used remote sensing data from Mars Reconnaissance Orbiter(MRO;NASA), Mars Global Surveyor(MGS;NASA), Mars Odyssey(NASA) and Mars Express(MEX;ESA) to devise an exploration strategy for one such area known as Hebrus Valles, which is a potential site for human exploration of the surface of Mars. A geological context map of the Hebrus Valles and Hephaestus Fossae region has been prepared and a candidate landing site has been proposed in the Hebrus Valles region. Suitable rover paths have been worked out from the proposed landing site for harnessing the science and resource potential of the region. The proposed landing site is located in the equatorial region at(20?40′N, 126?23′E) and due to its proximity to the Potential Subsurface Access Candidates(PSACs) in the region, such as sinkholes and skylights and also other resources such as crater ejecta, silicate material and fluvial channels, the site is appropriate for exploration of the region.展开更多
Possible bulk compositions of the super-Earth exoplanets CoRoT-7b, Kepler-9d, and Kepler-10b are investigated by applying a commonly used silicate model and a non-standard carbon model. Their internal structures are d...Possible bulk compositions of the super-Earth exoplanets CoRoT-7b, Kepler-9d, and Kepler-10b are investigated by applying a commonly used silicate model and a non-standard carbon model. Their internal structures are deduced using a suitable equation of state for the materials. The degeneracy problems of their compo- sitions can be partly overcome, based on the fact that all three planets are extremely close to their host stars. By analyzing the numerical results, we conclude： 1） the iron core of CoRoT-7b is not more than 27% of its total mass within lc~ mass-radius error bars, so an Earth-like composition is less likely, but its carbon rich model can be com- patible with an Earth-like core/mantle mass fraction; 2） Kepler-10b is more likely to have a Mercury-like composition, with its old age implying that its high iron content may be a result of strong solar wind or giant impact; 3） the transiting-only super-Earth Kepler-9d is also discussed. Combining its possible composition with the formation theory, we can place some constraints on its mass and bulk composition.展开更多
Martian caves have revived interest in the field of subsurface exploration because they are the potential destinations for future human habitats and astrobiological research.There are many pits on Mars,but some of the...Martian caves have revived interest in the field of subsurface exploration because they are the potential destinations for future human habitats and astrobiological research.There are many pits on Mars,but some of them look like collapsed cave roofs.These special pits are formed by the collapse of surface materials into the subsurface void spaces.The signature of life is probable in a subsurface cave on Mars as the subsurface environment can protect life from the harsh and dangerous radiation environment of the surface.In a cave,there may be an abundance of minerals,fluids,and other key resources.Therefore,locating the access point of the subsurface cave is essential and crucial for formulating plans for robotic/human explorations of the Red Planet,Mars.We have used remote sensing data from Mars Reconnaissance Orbiter(MRO;NASA),Mars Global Surveyor(MGS;NASA),and Mars Odyssey(NASA)for identifying,mapping,and classifying selected special pit candidates on the flank of Elysium Mons,Mars.A total of 32 special pit candidates has been identified and classified based upon morphology and geological context.Out of these,26 are newly discovered ones.The thermal behavior of 23 special pit candidates confirms that the special pits are radiating heat energy at nighttime,similar to potential caves.Also,cave entrances have been detected in nine candidates using data from the Hi RISE camera onboard MRO.These sites could be important destinations for future robotic/human exploration and the search for life on Mars.展开更多
We report the transit observations of the ultra-hot Jupiter WASP-121b using the Goodman High Throughput Spectrograph at the 4 m ground-based Southern Astrophysical Research Telescope,covering the wavelength range502-9...We report the transit observations of the ultra-hot Jupiter WASP-121b using the Goodman High Throughput Spectrograph at the 4 m ground-based Southern Astrophysical Research Telescope,covering the wavelength range502-900 nm.By dividing the target and reference star into 19 spectroscopic passbands and applying differential spectrophotometry,we derive spectroscopic transit light curves and fit them using a Gaussian process framework to determine transit depths for every passband.The obtained optical transmission spectrum shows a steep increased slope toward the blue wavelength,which seems to be too steep to be accounted for by Rayleigh scattering alone.We note that the transmission spectrum from this work and other works differ obviously from each other,which was pointed out previously by Wilson et al.as evidence for temporal atmospheric variation.We perform a free chemistry retrieval analysis on the optical transmission spectra from this work and the literature HST/WFC3 NIR spectrum.We determine TiO,VO and H_(2)O with abundances of-5.95_(-0.42)^(+0.47)dex,-6.72_(-1.79)^(+0.51)dex and-4.13_(-0.46)^(+0.63)dex,respectively.We compare the abundances of all three of these molecules derived from this work and previous works,and find that they are not consistent with each other,indicating the chemical compositions of the terminator region may change over long timescales.Future multi-epoch and high-precision transit observations are required to further confirm this phenomenon.We note that when combining the transmission spectra in the optical and in NIR in retrieval analysis,the abundances of V and VO,the NIR-to-optical offset and the cloud deck pressure may be coupled with each other.展开更多
A model is developed to study the ionospheric ion flux distribution along magnetic force lines in Martian magnetosphere and the influence of Martian intrinsic moment on the distribution. It is discovered that the intr...A model is developed to study the ionospheric ion flux distribution along magnetic force lines in Martian magnetosphere and the influence of Martian intrinsic moment on the distribution. It is discovered that the intrinsic moment has significant influence on the O+ ion flux distribution that a lower flux in the magnetotail will be associated with a stronger intrinsic moment. According to the theoretical result and the observed data on the ion flux which is about 7.6 × 106 cm-2 s-1 in the Martian magnetotail, the deduced Martian moment is about 2×1021 G cm3. This agrees well with the most recent data obtained by MAG/ER on the Mars Global Surveyor spacecraft.展开更多
Mutual events between natural satellites include mutual occultation and mutual eclipse. Mutual eclipse is another kind of mutual occultation as viewed from the center of the Sun instead of the Earth. Two mutual eclips...Mutual events between natural satellites include mutual occultation and mutual eclipse. Mutual eclipse is another kind of mutual occultation as viewed from the center of the Sun instead of the Earth. Two mutual eclipses of J2 Europa by J1 Io （2009 Aug. 28 and Sept. 12） were observed at Yunnan Observatory during the PHEMU09 international campaign. We will calculate the astrometric data of these Galilean satellites by analyzing and fitting the light curves we obtained. The limb-darkening was considered during modeling the light intensity of eclipsed satellites in the penumbra zone, by taking the Lommel-Seeliger scattering law into account. Several dynamical quantifies, such as the relative coordinates of the eclipsing satellite from the eclipsed one △α cos δ and △δ, impact parameter and mid-time corresponding to the impact parameter and the deviations O - C of observed △α cos d and △δ relative to ephemerides, were obtained for each event respectively.展开更多
基金Supported by the National Natural Science Foundation of China.
文摘We describe and analyze observations of mutual events of Galilean satellites made at the Yunnan Observatory in February 2003 from CCD imaging for the first time in China. Astrometric positions were deduced from these photometric observations by modelling the relative motion and the photometry of the involved satellites during each event.
基金Supported by the National Natural Science Foundation of China.
文摘The relationship between the k<SUB>2</SUB>/Q of the Galilean satellites and the k<SUB>2J</SUB>/Q<SUB>J</SUB> of Jupiter is derived from energy and momentum considerations. Calculations suggest that the Galilean satellites can be divided into two classes according to their Q values: Io and Ganymede have values between 10 and 50, while Europa and Callisto have values ranging from 200 to 700. The tidal contributions of the Galilean satellites to Jupiter's rotation are estimated. The main deceleration of Jupiter, which is about 99.04% of the total, comes from Io.
基金the financial support from the National Key R&D Program of China(2020YFC2201400)National Natural Science Foundation of China(NSFC,Grant Nos.12073092,12103097,and 12103098)+5 种基金the science research grants from the China Manned Space Project(No.CMS-CSST-2021-B09,B12)Guangzhou Basic and Applied Basic Research Program(202102080371)the Strategic Priority Program on Space Science,the Chinese Academy of Sciences(Grant No.XDA15020601)China Postdoctoral Science Foundation(No.2020M672936)the Fundamental Research Funds for the Central Universities,Sun Yat-sen University,Hainan Provincial Natural Science Foundation of China under Grant No.122RC546the National Natural Science Foundation of China under grant Nos.12063001。
文摘The nearby bright M-dwarf star L 98–59 has three terrestrial-sized planets.One challenge remaining in characterizing atmospheres around such planets is that it is not known a priori whether they possess any atmospheres.Here we report on study of the atmospheres of L 98–59 c and L 98–59 d using near-infrared spectral data from the G141 grism of Hubble Space Telescope(HST)/Wide Field Camera 3.We can reject the hypothesis of a clear atmosphere dominated by hydrogen and helium at a confidence level of ~3σ for both planets.Thus they could have a primary hydrogen-dominated atmosphere with an opaque cloud layer,or could have lost their primary hydrogen-dominated atmosphere and re-established a secondary thin atmosphere,or have no atmosphere at all.We cannot distinguish between these scenarios for the two planets using the current HST data.Future observations with the James Webb Space Telescope would be capable of confirming the existence of atmospheres around L 98–59 c and d and determining their compositions.
基金supported in part by the National Natural Science Foundation of China (NSFC, Grant Nos. 11073009, 10873006, 11373019 and 10573007)by three grants from Jilin University
文摘A prominent observation of the solar system is that the mass and gas content of Jovian planets decrease outward with orbital radius, except that, in terms of these properties, Neptune is almost the same as Uranus. In previous studies, the solar nebula was assumed to preexist and the formation process of the solar nebula was not considered. It was therefore assumed that planet formation at different radii started at the same time in the solar nebula. We show that planet formation at different radii does not start at the same time and is delayed at large radii. We suggest that this delay might be one of the factors that causes the outward decrease in the masses of Jovian planets. The nebula starts to form from its inner part because of the inside-out collapse of its progenitorial molecular cloud core. The nebula then expands outward due to viscosity. Material first reaches a small radius and then reaches a larger radius, so planet formation is delayed at the large radius. The later the material reaches a planet＇s location, the less time it has to gain mass and gas content. Hence, the delay tends to cause the outward decrease in mass and gas content of Jovian planets. Our nebula model shows that the material reaches Jupiter, Saturn, Uranus and Neptune at t = 0.40, 0.57, 1.50 and 6.29 × 10^6 yr, respectively. We discuss the effects of time delay on the masses of Jovian planets in the framework of the core accretion model of planet formation. Saturn＇s formation is not delayed by much time relative to Jupiter so that they both reach the rapid gas accretion phase and become gas giants. However, the delay in formation of Uranus and Neptune is long and might be one of the factors that cause them not to reach the rapid gas accretion phase before the gas nebula is dispersed. Saturn has less time to go through the rapid gas accretion, so Saturn＇s mass and gas content are significantly less than those of Jupiter.
文摘Mars is the only extraterrestrial body which could host primitive lifeforms and also has the potential to host a human base in the near future. Towards fulfilling these objectives, several remote sensing missions and rover based missions have been sent to Mars. Still, confirmation of existing or extinct life on this planet in any form has not been achieved and possibly human missions at selected sites in the future are the key to addressing this problem. Here, we have used remote sensing data from Mars Reconnaissance Orbiter(MRO;NASA), Mars Global Surveyor(MGS;NASA), Mars Odyssey(NASA) and Mars Express(MEX;ESA) to devise an exploration strategy for one such area known as Hebrus Valles, which is a potential site for human exploration of the surface of Mars. A geological context map of the Hebrus Valles and Hephaestus Fossae region has been prepared and a candidate landing site has been proposed in the Hebrus Valles region. Suitable rover paths have been worked out from the proposed landing site for harnessing the science and resource potential of the region. The proposed landing site is located in the equatorial region at(20?40′N, 126?23′E) and due to its proximity to the Potential Subsurface Access Candidates(PSACs) in the region, such as sinkholes and skylights and also other resources such as crater ejecta, silicate material and fluvial channels, the site is appropriate for exploration of the region.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10833001 and 10925313)Ph.D traininggrant of China (20090091110002)+1 种基金Fundamental Research Funds for the Central Universities(No. 1112020102)support from the Shandong Provincial Natural Science Foundation,China (ZR2010AQ023)
文摘Possible bulk compositions of the super-Earth exoplanets CoRoT-7b, Kepler-9d, and Kepler-10b are investigated by applying a commonly used silicate model and a non-standard carbon model. Their internal structures are deduced using a suitable equation of state for the materials. The degeneracy problems of their compo- sitions can be partly overcome, based on the fact that all three planets are extremely close to their host stars. By analyzing the numerical results, we conclude： 1） the iron core of CoRoT-7b is not more than 27% of its total mass within lc~ mass-radius error bars, so an Earth-like composition is less likely, but its carbon rich model can be com- patible with an Earth-like core/mantle mass fraction; 2） Kepler-10b is more likely to have a Mercury-like composition, with its old age implying that its high iron content may be a result of strong solar wind or giant impact; 3） the transiting-only super-Earth Kepler-9d is also discussed. Combining its possible composition with the formation theory, we can place some constraints on its mass and bulk composition.
文摘Martian caves have revived interest in the field of subsurface exploration because they are the potential destinations for future human habitats and astrobiological research.There are many pits on Mars,but some of them look like collapsed cave roofs.These special pits are formed by the collapse of surface materials into the subsurface void spaces.The signature of life is probable in a subsurface cave on Mars as the subsurface environment can protect life from the harsh and dangerous radiation environment of the surface.In a cave,there may be an abundance of minerals,fluids,and other key resources.Therefore,locating the access point of the subsurface cave is essential and crucial for formulating plans for robotic/human explorations of the Red Planet,Mars.We have used remote sensing data from Mars Reconnaissance Orbiter(MRO;NASA),Mars Global Surveyor(MGS;NASA),and Mars Odyssey(NASA)for identifying,mapping,and classifying selected special pit candidates on the flank of Elysium Mons,Mars.A total of 32 special pit candidates has been identified and classified based upon morphology and geological context.Out of these,26 are newly discovered ones.The thermal behavior of 23 special pit candidates confirms that the special pits are radiating heat energy at nighttime,similar to potential caves.Also,cave entrances have been detected in nine candidates using data from the Hi RISE camera onboard MRO.These sites could be important destinations for future robotic/human exploration and the search for life on Mars.
基金supported by the National Key R&D Program of China Nos.2019YFA0405102 and 2019YFA0405502the National Natural Science Foundation of China(NSFC,Grant Nos.42075123,62127901,11988101,42005098,and 12073044)+1 种基金supported by the China Manned Space Project with No.CMS-CSST-2021-B12supported by the Chinese Academy of Sciences(CAS),through a grant to the CAS South America Center for Astronomy(CASSACA)in Santiago,Chile。
文摘We report the transit observations of the ultra-hot Jupiter WASP-121b using the Goodman High Throughput Spectrograph at the 4 m ground-based Southern Astrophysical Research Telescope,covering the wavelength range502-900 nm.By dividing the target and reference star into 19 spectroscopic passbands and applying differential spectrophotometry,we derive spectroscopic transit light curves and fit them using a Gaussian process framework to determine transit depths for every passband.The obtained optical transmission spectrum shows a steep increased slope toward the blue wavelength,which seems to be too steep to be accounted for by Rayleigh scattering alone.We note that the transmission spectrum from this work and other works differ obviously from each other,which was pointed out previously by Wilson et al.as evidence for temporal atmospheric variation.We perform a free chemistry retrieval analysis on the optical transmission spectra from this work and the literature HST/WFC3 NIR spectrum.We determine TiO,VO and H_(2)O with abundances of-5.95_(-0.42)^(+0.47)dex,-6.72_(-1.79)^(+0.51)dex and-4.13_(-0.46)^(+0.63)dex,respectively.We compare the abundances of all three of these molecules derived from this work and previous works,and find that they are not consistent with each other,indicating the chemical compositions of the terminator region may change over long timescales.Future multi-epoch and high-precision transit observations are required to further confirm this phenomenon.We note that when combining the transmission spectra in the optical and in NIR in retrieval analysis,the abundances of V and VO,the NIR-to-optical offset and the cloud deck pressure may be coupled with each other.
文摘A model is developed to study the ionospheric ion flux distribution along magnetic force lines in Martian magnetosphere and the influence of Martian intrinsic moment on the distribution. It is discovered that the intrinsic moment has significant influence on the O+ ion flux distribution that a lower flux in the magnetotail will be associated with a stronger intrinsic moment. According to the theoretical result and the observed data on the ion flux which is about 7.6 × 106 cm-2 s-1 in the Martian magnetotail, the deduced Martian moment is about 2×1021 G cm3. This agrees well with the most recent data obtained by MAG/ER on the Mars Global Surveyor spacecraft.
基金supported by the National Basic Research Program of China(973 Program Grant No. 2011CB811400)the Joint Doctoral Promotion Programme of the Chinese Academy of Science
文摘Mutual events between natural satellites include mutual occultation and mutual eclipse. Mutual eclipse is another kind of mutual occultation as viewed from the center of the Sun instead of the Earth. Two mutual eclipses of J2 Europa by J1 Io （2009 Aug. 28 and Sept. 12） were observed at Yunnan Observatory during the PHEMU09 international campaign. We will calculate the astrometric data of these Galilean satellites by analyzing and fitting the light curves we obtained. The limb-darkening was considered during modeling the light intensity of eclipsed satellites in the penumbra zone, by taking the Lommel-Seeliger scattering law into account. Several dynamical quantifies, such as the relative coordinates of the eclipsing satellite from the eclipsed one △α cos δ and △δ, impact parameter and mid-time corresponding to the impact parameter and the deviations O - C of observed △α cos d and △δ relative to ephemerides, were obtained for each event respectively.
