We analyze MESSENGER reflectance measurements covering the northern polar region of Mercury,the least studied region of the northern mercurian hemisphere.We use observations from the Mercury Dual Imaging System Wide-A...We analyze MESSENGER reflectance measurements covering the northern polar region of Mercury,the least studied region of the northern mercurian hemisphere.We use observations from the Mercury Dual Imaging System Wide-Angle Camera(MDIS/WAC)and the Mercury Atmospheric and Surface Composition Spectrometer(MASCS/VIRS)to study the spectral dependence of the surface reflectance.The results obtained from the observations made by both instruments are remarkably consistent.We find that a second degree polynomial description of the measured reflectance spectra gives very good fits to the data and that the information that they carry can best be characterized by two parameters,the mean reflectance and the mean relative spectral slope,averaged over the explored range of wavelengths.The properties of the four main types of terrains known to form Mercury’s regolith in the northern region,smooth plains(SPs),heavily cratered terrain(HCT),fresh ejecta/materials and red pitted ground(RPG),are examined in terms of these two parameters.The results are compared,and found consistent with those obtained by earlier studies in spite of difficulties met in obtaining accurate reflectance measurements under the large incidence angle condition characteristic of polar regions.These results will help with the preparation of the BepiColombo mission and with supporting its observational strategy.展开更多
Transit Timing Variation(TTV)of hot Jupiters provides direct observational evidence of planet tidal dissipation.Detecting tidal dissipation through TTV needs high precision transit timings and long timing baselines.In...Transit Timing Variation(TTV)of hot Jupiters provides direct observational evidence of planet tidal dissipation.Detecting tidal dissipation through TTV needs high precision transit timings and long timing baselines.In this work,we predict and discuss the potential scientific contribution of the SiTian Survey in detecting and analyzing exoplanet TTV.We develop a tidal dissipation detection pipeline for the SiTian Survey that aims at time-domain astronomy with 721 m optical telescopes.The pipeline includes the modules of light curve deblending,transit timing acquisition and TTV modeling.SiTian is capable of detecting more than 25,000 exoplanets among which we expect~50 sources to show evidence of tidal dissipation.We present detection and analysis of tidal dissipating targets,based on simulated SiTian light curves of XO-3b and WASP-161 b.The transit light curve modeling gives consistent results within 1σto input values of simulated light curves.Also,the parameter uncertainties predicted by Markov Chain Monte Carlo are consistent with the distribution obtained from simulating and modeling the light curve 1000 times.The timing precision of SiTian observations is~0.5 minutes with one transit visit.We show that differences between TTV origins,e.g.,tidal dissipation,apsidal precession and multiple planets,would be significant,considering the timing precision and baseline.The detection rate of tidal dissipating hot Jupiters would answer a crucial question of whether the planet migrates at an early formation stage or random stages due to perturbations,e.g.,planet scattering or secular interaction.SiTian identified targets would be constructive given that the sample would extend tenfold.展开更多
基金Financial support from Centre National E.Etudes Spatiales(CNES),USTH is gratefully acknowledged.
文摘We analyze MESSENGER reflectance measurements covering the northern polar region of Mercury,the least studied region of the northern mercurian hemisphere.We use observations from the Mercury Dual Imaging System Wide-Angle Camera(MDIS/WAC)and the Mercury Atmospheric and Surface Composition Spectrometer(MASCS/VIRS)to study the spectral dependence of the surface reflectance.The results obtained from the observations made by both instruments are remarkably consistent.We find that a second degree polynomial description of the measured reflectance spectra gives very good fits to the data and that the information that they carry can best be characterized by two parameters,the mean reflectance and the mean relative spectral slope,averaged over the explored range of wavelengths.The properties of the four main types of terrains known to form Mercury’s regolith in the northern region,smooth plains(SPs),heavily cratered terrain(HCT),fresh ejecta/materials and red pitted ground(RPG),are examined in terms of these two parameters.The results are compared,and found consistent with those obtained by earlier studies in spite of difficulties met in obtaining accurate reflectance measurements under the large incidence angle condition characteristic of polar regions.These results will help with the preparation of the BepiColombo mission and with supporting its observational strategy.
基金supported by funding from the Cultivation Project for LAMOST Scientific Payoff and Research Achievement of CAMS-CASthe National Natural Science Foundation of China(NSFC+4 种基金No.11872246,12041301)the Beijing Natural Science Foundation(No.1202015)supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11988101 and 42075123)the National Key RD Program of China No.2019YFA0405102the science research grants from the China Manned Space Project with NO.CMS-CSST-2021-B12。
文摘Transit Timing Variation(TTV)of hot Jupiters provides direct observational evidence of planet tidal dissipation.Detecting tidal dissipation through TTV needs high precision transit timings and long timing baselines.In this work,we predict and discuss the potential scientific contribution of the SiTian Survey in detecting and analyzing exoplanet TTV.We develop a tidal dissipation detection pipeline for the SiTian Survey that aims at time-domain astronomy with 721 m optical telescopes.The pipeline includes the modules of light curve deblending,transit timing acquisition and TTV modeling.SiTian is capable of detecting more than 25,000 exoplanets among which we expect~50 sources to show evidence of tidal dissipation.We present detection and analysis of tidal dissipating targets,based on simulated SiTian light curves of XO-3b and WASP-161 b.The transit light curve modeling gives consistent results within 1σto input values of simulated light curves.Also,the parameter uncertainties predicted by Markov Chain Monte Carlo are consistent with the distribution obtained from simulating and modeling the light curve 1000 times.The timing precision of SiTian observations is~0.5 minutes with one transit visit.We show that differences between TTV origins,e.g.,tidal dissipation,apsidal precession and multiple planets,would be significant,considering the timing precision and baseline.The detection rate of tidal dissipating hot Jupiters would answer a crucial question of whether the planet migrates at an early formation stage or random stages due to perturbations,e.g.,planet scattering or secular interaction.SiTian identified targets would be constructive given that the sample would extend tenfold.
