Contrary to the solar system,most exoplanet systems detected hitherto are close-in and compact.One typical system is TRAPPIST-1,which has seven nearly co-planar terrestrial planets all within the orbit of Mercury,incl...Contrary to the solar system,most exoplanet systems detected hitherto are close-in and compact.One typical system is TRAPPIST-1,which has seven nearly co-planar terrestrial planets all within the orbit of Mercury,including three in the habitable zone.To evaluate the differences in developing sophisticated gravity theories from the solar system,we use N-body integrations to simulate ephemeris and reproduce some important astronomy phenomena observed on the potentially habitable planet TRAPPIST-1e.Retrograde motions of other planets last 1-2 orders of magnitude shorter than in the solar system,but occur much more frequently.Transit events of all inner planets can be observed steadily.Except for Kepler's first law,which is hard to notice for low eccentricities of planets,the other two laws can then be precisely verified in 102 days,because the areas swept by planets vary by0.01%and the observed semimajor axes and periods result in constants with theoretical and observation accuracies both2%.However,the mean motion correlation implies that the Great Inequality is not always apparent between one pair of planets like Jupiter and Saturn.Furthermore,general relativity can hardly be discovered because it gives rise to perihelion precession of inner planets only~0.1%of gravity precession,dozens of times smaller than Mercury.Our results support the possibility of developing part of gravity theories by potential exo-civilizations in compact systems like TRAPPIST-1.展开更多
The astrometry method has great advantages in searching for exoplanets in the habitable zone around solar-like stars. However, the presence of multiple planets may cause a problem with degeneracy when trying to comput...The astrometry method has great advantages in searching for exoplanets in the habitable zone around solar-like stars. However, the presence of multiple planets may cause a problem with degeneracy when trying to compute accurate planet parameters from observation data and reduce detectability. The degeneracy problem is extremely critical, especially in a space mission which has limited observation time and cadence. In this series of papers, we study the detectability of habitable Earth-mass planets in different types of multi-planet systems, aiming to find the most favorable targets for the potential space mission–Habitable ExoPlanet Survey(HEPS). In the first paper, we present an algorithm to find planets in the habitable zone around solar-like stars using astrometry. We find the detectability can be well described by planets' signal-to-noise ratio(SNR) and a defined parameter S = M2/(T1-T2)2, where M2 and T2are the mass and period of the second planet, respectively. T1 is the period of the planet in the habitable zone. The parameter S represents the influence of planetary architectures. We fit the detectability as a function of both the SNR of the planet in the habitable zone and the parameter S. An Earth-like planet in a habitable zone is harder to detect(with detectability PHP< 80%) in a system with a hot Jupiter or warm Jupiter(within2 AU), in which the parameter S is large. These results can be used in target selections and to determine the priority of target stars for HEPS, especially when we select and rank nearby planet hosts with a single planet.展开更多
In January, 2008 the Chinese Small Telescope ARray （CSTAR） was suc-cessfully deployed at Dome A, Antarctica. Because CSTAR consists of four static14.5 cm telescopes pointing at the same 4.5° x 4.5° field a...In January, 2008 the Chinese Small Telescope ARray （CSTAR） was suc-cessfully deployed at Dome A, Antarctica. Because CSTAR consists of four static14.5 cm telescopes pointing at the same 4.5° x 4.5° field around the south celestialpole, diurnal motion can be seen in its field of view. The stars are centered at differentpositions in different exposure frames. During four months of continuous observationsduring the polar night of 2008, about 0.3 million/-band images were obtained. In thelatest version of the released photometric catalog, the effects of diurnal motion of thestars on the static CSTAR optical system can be obviously found. In this work, weupdate the CSTAR catalog by carefully analyzing and correcting the systematic errorscaused by diurnal motion of stars on imperfectly flat-fielded frames.展开更多
HEPS(Habitable ExoPlanet Survey) is a planning astrometry satellite that aims to find Earth-like planets in the solar neighbourhood. In this paper, we selected 140 planet harboring stars within 30 pc of the solar syst...HEPS(Habitable ExoPlanet Survey) is a planning astrometry satellite that aims to find Earth-like planets in the solar neighbourhood. In this paper, we selected 140 planet harboring stars within 30 pc of the solar system to be potential targets for HEPS. We calculate the detection probability of the planet in habitable zone(HZ) for each system using the simulated data of astrometry measurements. For those host stars without planets in HZ, we inject an additional planet of 10 M⊕ in their HZs and check the stability of the systems. Considering five observation modes of different sampling cadence and total observation time, we obtain a table containing the total detection probability of the planets in HZs for all of the 140 selected systems. This paper provides a potential ranked list of target stars for HEPS, or other astrometric mission to detect Earth-like planets in the future. We also calculate an empirical fitted expression of the detection probability as a function of both sampling cadence and total observation time. We conclude a quantitative method to estimate the detection probability for certain planet hosts and observation modes via the empirical expression. We show the minimum requirements of both sampling cadence and observation time for Proxima Centauri, HD 189733 and HD 102365, if the detection probability of habitable-zone planets of these three systems needs to be 90%.展开更多
We present the results of our recent study on the interactions between a giant planet and a self-gravitating gas disk. We investigate how the disk＇s self-gravity affects the gap formation process and the migration of...We present the results of our recent study on the interactions between a giant planet and a self-gravitating gas disk. We investigate how the disk＇s self-gravity affects the gap formation process and the migration of the giant planet. Two series of 1-D and 2-D hydrodynamic simulations are performed. We select several surface densities and focus on the gravitationally stable region. To obtain more reliable gravity torques exerted on the planet, a refined treatment of the disk＇s gravity is adopted in the vicinity of the planet. Our results indicate that the net effect of the disk＇s self- gravity on the gap formation process depends on the surface density of the disk. We notice that there are two critical values, ∑I and ∑n. When the surface density of the disk is lower than the first one,∑0 〈 ∑I, the effect of self-gravity suppresses the formation of a gap. When ∑0 〉 ∑I, the self-gravity of the gas tends to benefit the gap formation process and enlarges the width/depth of the gap. According to our 1-D and 2-D simulations, we estimate the first critical surface density to be ∑I ≈ 0.8 MMSN. This effect increases until the surface density reaches the second critical value ∑n- When ∑0 〉 ∑n, the gravitational turbulence in the disk becomes dominant and the gap formation process is suppressed again. Our 2-D simulations show that this critical surface density is around 3.5 MMSN. We also study the associated orbital evolution of a giant planet. Under the effect of the disk＇s self-gravity, the migration rate of the giant planet increases when the disk is dominated by gravitational turbulence. We show that the migration timescale correlates with the effective viscosity and can be up to 104 yr.展开更多
基金supported by the National Key R&D Program of China(2019YFA0706601)the National Natural Science Foundation of China(grant Nos.11973028,11933001,1803012,12150009,and 42005045)+3 种基金Science and Technology Foundation of Zhejiang Ocean University(No.2021C21021)Key Laboratory of Modern Astronomy and Astrophysics(Nanjing University),Ministry of Educationthe science research grants from the Civil Aerospace Technology Research Project(D010102)as well as the China Manned Space Project with NO.CMS-CSST-2021-B12 and CMSCSST-2021-B09.
文摘Contrary to the solar system,most exoplanet systems detected hitherto are close-in and compact.One typical system is TRAPPIST-1,which has seven nearly co-planar terrestrial planets all within the orbit of Mercury,including three in the habitable zone.To evaluate the differences in developing sophisticated gravity theories from the solar system,we use N-body integrations to simulate ephemeris and reproduce some important astronomy phenomena observed on the potentially habitable planet TRAPPIST-1e.Retrograde motions of other planets last 1-2 orders of magnitude shorter than in the solar system,but occur much more frequently.Transit events of all inner planets can be observed steadily.Except for Kepler's first law,which is hard to notice for low eccentricities of planets,the other two laws can then be precisely verified in 102 days,because the areas swept by planets vary by0.01%and the observed semimajor axes and periods result in constants with theoretical and observation accuracies both2%.However,the mean motion correlation implies that the Great Inequality is not always apparent between one pair of planets like Jupiter and Saturn.Furthermore,general relativity can hardly be discovered because it gives rise to perihelion precession of inner planets only~0.1%of gravity precession,dozens of times smaller than Mercury.Our results support the possibility of developing part of gravity theories by potential exo-civilizations in compact systems like TRAPPIST-1.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11503009, 11333002 and 11673011)the Heising-Simons Foundation+1 种基金the Fundamental Research Funds for the Central Universities (Nos. 14380018 and 14380023)the Technology of Space Telescope Detecting Exoplanet and Life supported by the National Defense Science and Engineering Bureau civil spaceflight advanced research project D030201
文摘The astrometry method has great advantages in searching for exoplanets in the habitable zone around solar-like stars. However, the presence of multiple planets may cause a problem with degeneracy when trying to compute accurate planet parameters from observation data and reduce detectability. The degeneracy problem is extremely critical, especially in a space mission which has limited observation time and cadence. In this series of papers, we study the detectability of habitable Earth-mass planets in different types of multi-planet systems, aiming to find the most favorable targets for the potential space mission–Habitable ExoPlanet Survey(HEPS). In the first paper, we present an algorithm to find planets in the habitable zone around solar-like stars using astrometry. We find the detectability can be well described by planets' signal-to-noise ratio(SNR) and a defined parameter S = M2/(T1-T2)2, where M2 and T2are the mass and period of the second planet, respectively. T1 is the period of the planet in the habitable zone. The parameter S represents the influence of planetary architectures. We fit the detectability as a function of both the SNR of the planet in the habitable zone and the parameter S. An Earth-like planet in a habitable zone is harder to detect(with detectability PHP< 80%) in a system with a hot Jupiter or warm Jupiter(within2 AU), in which the parameter S is large. These results can be used in target selections and to determine the priority of target stars for HEPS, especially when we select and rank nearby planet hosts with a single planet.
基金Supported by the National Natural Science Foundation of China
文摘In January, 2008 the Chinese Small Telescope ARray （CSTAR） was suc-cessfully deployed at Dome A, Antarctica. Because CSTAR consists of four static14.5 cm telescopes pointing at the same 4.5° x 4.5° field around the south celestialpole, diurnal motion can be seen in its field of view. The stars are centered at differentpositions in different exposure frames. During four months of continuous observationsduring the polar night of 2008, about 0.3 million/-band images were obtained. In thelatest version of the released photometric catalog, the effects of diurnal motion of thestars on the static CSTAR optical system can be obviously found. In this work, weupdate the CSTAR catalog by carefully analyzing and correcting the systematic errorscaused by diurnal motion of stars on imperfectly flat-fielded frames.
基金supported by the National Natural Science Foundation of China(Grant Nos.11503009,11973028,11933001,11673011 and11803012)supported by the National Defense Science and Engineering Bureau civil spaceflight advanced research project D030201support of Program A for Outstanding PhD candidates of Nanjing University.
文摘HEPS(Habitable ExoPlanet Survey) is a planning astrometry satellite that aims to find Earth-like planets in the solar neighbourhood. In this paper, we selected 140 planet harboring stars within 30 pc of the solar system to be potential targets for HEPS. We calculate the detection probability of the planet in habitable zone(HZ) for each system using the simulated data of astrometry measurements. For those host stars without planets in HZ, we inject an additional planet of 10 M⊕ in their HZs and check the stability of the systems. Considering five observation modes of different sampling cadence and total observation time, we obtain a table containing the total detection probability of the planets in HZs for all of the 140 selected systems. This paper provides a potential ranked list of target stars for HEPS, or other astrometric mission to detect Earth-like planets in the future. We also calculate an empirical fitted expression of the detection probability as a function of both sampling cadence and total observation time. We conclude a quantitative method to estimate the detection probability for certain planet hosts and observation modes via the empirical expression. We show the minimum requirements of both sampling cadence and observation time for Proxima Centauri, HD 189733 and HD 102365, if the detection probability of habitable-zone planets of these three systems needs to be 90%.
基金Supported by the National Natural Science Foundation of China
文摘We present the results of our recent study on the interactions between a giant planet and a self-gravitating gas disk. We investigate how the disk＇s self-gravity affects the gap formation process and the migration of the giant planet. Two series of 1-D and 2-D hydrodynamic simulations are performed. We select several surface densities and focus on the gravitationally stable region. To obtain more reliable gravity torques exerted on the planet, a refined treatment of the disk＇s gravity is adopted in the vicinity of the planet. Our results indicate that the net effect of the disk＇s self- gravity on the gap formation process depends on the surface density of the disk. We notice that there are two critical values, ∑I and ∑n. When the surface density of the disk is lower than the first one,∑0 〈 ∑I, the effect of self-gravity suppresses the formation of a gap. When ∑0 〉 ∑I, the self-gravity of the gas tends to benefit the gap formation process and enlarges the width/depth of the gap. According to our 1-D and 2-D simulations, we estimate the first critical surface density to be ∑I ≈ 0.8 MMSN. This effect increases until the surface density reaches the second critical value ∑n- When ∑0 〉 ∑n, the gravitational turbulence in the disk becomes dominant and the gap formation process is suppressed again. Our 2-D simulations show that this critical surface density is around 3.5 MMSN. We also study the associated orbital evolution of a giant planet. Under the effect of the disk＇s self-gravity, the migration rate of the giant planet increases when the disk is dominated by gravitational turbulence. We show that the migration timescale correlates with the effective viscosity and can be up to 104 yr.
