Hubble WFC3 Spectroscopy of the Terrestrial Planets L 98–59c and d:No Evidence for a Clear Hydrogen Dominated Primary Atmosphere

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.

Relation between Mass and Radius of Exoplanets Distinguished by their Density

The formation of the solar system has been studied since the 18th century and received a boost in 1995 with the discovery of the first exoplanet,51 Pegasi b.The investigations increased the number of confirmed planets to about5400 to date.The possible internal structure and composition of these planets can be inferred from the relationship between planet mass and radius,M-R.We have analyzed the M-R relation of a selected sample of iron-rock and ice-gas planets using a fractal approach to their densities.The application of fractal theory is particularly useful to define the physical meaning of the proportionality constant and the exponent in an empirical M-R power law in exoplanets,but this does not necessarily mean that they have an internal fractal structure.The M-R relations based on this sample are M=(1.46±0.08)R^(2.6±0.2)for the rocky population(3.6≤ρ≤14.3 g cm^(-3)),with 1.5≤M≤39M_(⊕),and M=(0.27±0.04)R^(2.7±0.2)for ice-gas planets(0.3≤ρ≤2.1 g cm^(-3))with 5.1≤M≤639 M_(⊕)(or■2 M_(J))and orbital periods greater than 10 days.Both M-R relations have in their density range a great predictive power for the determination of the mass of exoplanets and even for the largest icy moons of the solar system.The average fractal dimension of these planets is D=2.6±0.1,indicating that these objects likely have a similar degree of heterogeneity in their densities and a nearly similar composition in each sample.The M-R diagram shows a"gap"between ice-gas and iron-rock planets.This gap is a direct consequence of the density range of these two samples.We empirically propose an upper mass limit of about 100 M_(⊕),so that an M-R relation for ice-gas planets in a narrow density range is defined by M∝R^(3).

Confirmation of a Sub-Saturn-size Transiting Exoplanet Orbiting a G Dwarf:TOI-1194 b and a Very Low Mass Companion Star: TOI-1251 B from TESS

We report the confirmation of a sub-Saturn-size exoplanet,TOI-1194 b,with a mass of about 0.456+0.055-0.051M_(J),and a very low mass companion star with a mass of about 96.5±1.5 MJ,TOI-1251 B.Exoplanet candidates provided by the Transiting Exoplanet Survey Satellite(TESS)are suitable for further follow-up observations by ground-based telescopes with small and medium apertures.The analysis is performed based on data from several telescopes worldwide,including telescopes in the Sino-German multiband photometric campaign,which aimed at confirming TESS Objects of Interest(TOIs)using ground-based small-aperture and medium-aperture telescopes,especially for long-period targets.TOI-1194 b is confirmed based on the consistent periodic transit depths from the multiband photometric data.We measure an orbital period of 2.310644±0.000001 days,the radius is 0.767+0.045-0.041RJ and the amplitude of the RV curve is 69.4_(-7.3)^(+7.9)m s^(-1).TOI-1251 B is confirmed based on the multiband photometric and high-resolution spectroscopic data,whose orbital period is 5.963054+0.000002-0.000001days,radius is 0.947+0.035-0.033 R_(J) and amplitude of the RV curve is 9849_(-40)^(+42)ms^(-1).

Atmospheric regimes and trends on exoplanets and brown dwarfs

A planetary atmosphere is the outer gas layer of a planet. Besides its scientific significance among the first and most accessible planetary layers observed from space, it is closely connected with planetary formation and evolution, surface and interior processes, and habitability of planets. Current theories of planetary atmospheres were primarily obtained through the studies of eight large planets, Pluto and three large moons(Io, Titan, and Triton) in the Solar System. Outside the Solar System, more than four thousand extrasolar planets(exoplanets) and two thousand brown dwarfs have been confirmed in our Galaxy, and their population is rapidly growing. The rich information from these exotic bodies offers a database to test, in a statistical sense, the fundamental theories of planetary climates. Here we review the current knowledge on atmospheres of exoplanets and brown dwarfs from recent observations and theories. This review highlights important regimes and statistical trends in an ensemble of atmospheres as an initial step towards fully characterizing diverse substellar atmospheres, that illustrates the underlying principles and critical problems.Insights are obtained through analysis of the dependence of atmospheric characteristics on basic planetary parameters. Dominant processes that influence atmospheric stability, energy transport, temperature, composition and flow pattern are discussed and elaborated with simple scaling laws. We dedicate this review to Dr. Adam P. Showman(1968–2020) in recognition of his fundamental contribution to the understanding of atmospheric dynamics on giant planets, exoplanets and brown dwarfs.

The snowline in the protoplanetary disk and extrasolar planets

We investigate the behavior of the snowline in a protoplanetary disk and the relationship between the radius of the snowline and properties of molecular cloud cores.In our disk model,we consider mass influx from the gravitational collapse of a molecular cloud core,irradiation from the central star,and thermal radiation from the ambient molecular cloud gas.As the protoplanetary disk evolves,the radius of the snowline increases first to a maximum value Rmax,and then decreases in the late stage of evolution of the protoplanetary disk.The value of Rmaxis dependent on the properties of molecular cloud cores(mass M;,angular velocity ω and temperature T;).Many previous works found that solid material tends to accumulate at the location of the snowline,which suggests that the snowline is the preferred location for giant planet formation.With these conclusions,we compare the values of R;with semimajor axes of giant planets in extrasolar systems,and find that Rmaxmay provide an upper limit for the locations of the formation of giant planets which are formed by the core accretion model.

Eclipses and Occultations of Galilean Satellites Observed at Yunnan Observatory in 2003

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.

An Independent Degree-eight Mars Gravity Field Model and the Expected Results from the Tianwen-1 Mission

Tianwen-1 is China's first independent interplanetary exploration mission,targeting Mars,and includes orbiting,landing,and rover phases.Similar to previous Mars missions,the Tianwen-1 orbiter was designed for polar orbits during the scientific mission period but has an exceptional eccentricity of approximately 0.59.We provide the first independent eight-degree Martian gravity field model in this paper,which was developed exclusively by a team working in China with our independent software as well,based on about two months of radiometric Doppler and range data from only the Tianwen-1 mission.This model is independent from the models created by the groups at NASA Jet Propulsion Laboratory and Goddard Space Flight Center in the United States,as well as the Centre National d'Etudes Spatiales in France.Furthermore,in order to optimize the engineering and scientific benefits,we proposed a number of potential orbits for the extended Tianwen-1 mission.In order to solve a higher-degree independent Mars gravity field model,the viability of modifying the perigee height was investigated,with the priority considerations of fuel savings and implementation hazards being controlled.

A Search for Exoplanets in Open Clusters and Young Associations based on TESS Objects of Interest

We report the results of our search for planet candidates in open clusters and young stellar associations based on the Transiting Exoplanet Survey Satellite(TESS) Objects of Interest Catalog.We find one confirmed planet,one promising candidate,one brown dwarf and three unverified planet candidates in a sample of 1229 open clusters from the second Gaia data release.We discuss individual planet-star systems based on their basic parameters,membership probability and the observation notes from the ExoFOP-TESS website.We also find ten planet candidates(P> 95%) in young stellar associations by using the BANYAN ∑ Multivariate Bayesian Algorithm.Among the ten candidates,five are known planetary systems.We estimate the rotation periods of the host stars using the TESS light curves and estimate their ages based on gyrochronology.Two candidates with periodic variations are likely to be young planets,but their exact memberships to young stellar associations remain unknown.

Delay of planet formation at large radius and the outward decrease in mass and gas content of Jovian planets

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.

Detection of TiO and VO in the Atmosphere of WASP-121b and Evidence For its Temporal Variation

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.

A tale of planet formation: from dust to planets

The characterization of exoplanets and their birth protoplanetary disks has enormously advanced in the last decade.Benefitting from that,our global understanding of the planet formation processes has been substantially improved.In this review,we first summarize the cutting-edge states of the exoplanet and disk observations.We further present a comprehensive panoptic view of modern core accretion planet formation scenarios,including dust growth and radial drift,planetesimal formation by the streaming instability,core growth by planetesimal accretion and pebble accretion.We discuss the key concepts and physical processes in each growth stage and elaborate on the connections between theoretical studies and observational revelations.Finally,we point out the critical questions and future directions of planet formation studies.

Mapping of Compositional Diversity and Chronological Ages of Lunar Farside Multiring Mare Moscoviense Basin:Implications to the Middle Imbrian Mare Basalts

The Mare Moscoviense is an astonishing rare flatland multi-ring basin and one of the recognizable mare regions on the Moon's farside.The mineralogical,chronological,topographical and morphological studies of the maria surface of the Moon provide a primary understanding of the origin and evolution of the mare provinces.In this study,the Chandrayaan-1 M^(3)data have been employed to prepare optical maturity index,FeO and TiO^(2)concentration,and standard band ratio map to detect the mafic indexes like olivine and pyroxene minerals.The crater size frequency distribution method has been applied to LROC WAC data to obtain the absolute model ages of the Moscoviense basin.The four geological unit ages were observed as 3.57 Ga(U-2),3.65 Ga(U-1),3.8 Ga(U-3)and 3.92 Ga(U-4),which could have been formed between the Imbrian and Nectarian epochs.The M^(3)imaging and reflectance spectral parameters were used to reveal the minerals like pyroxene,olivine,ilmenite,plagioclase,orthopyroxene-olivine-spinel lithology,and olivine-pyroxene mixtures present in the gabbroic basalt,anorthositic and massive ilmenite rocks,and validated with the existing database.The results show that the Moscoviense basin is dominated by intermediate TiO^(2)basalts that derived from olivine-ilmenite-pyroxene cumulate depths ranging from 200 to 500 km between 3.5 Ga and 3.6 Ga.

The Q Values of the Galilean Satellites and their Tidal Contributions to the Deceleration of Jupiter's Rotation

The relationship between the k2/Q of the Galilean satellites and the k2J/QJ 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.

Detecting and Monitoring Tidal Dissipation of Hot Jupiters in the Era of SiTian

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.

Detection and Classification of Potential Caves on the Flank of Elysium Mons,Mars

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.

CHES: A Space-borne Astrometric Mission for the Detection of Habitable Planets of the Nearby Solar-type Stars

The Closeby Habitable Exoplanet Survey(CHES) mission is proposed to discover habitable-zone Earth-like planets of nearby solar-type stars(~10 pc away from our solar system) via microarcsecond relative astrometry.The major scientific objectives of CHES are:to search for Earth Twins or terrestrial planets in habitable zones orbiting100 FGK nearby stars;further to conduct a comprehensive survey and extensively characterize nearby planetary systems.The primary payload is a high-quality,low-distortion,high-stability telescope.The optical subsystem is a coaxial three-mirror anastigmat(TMA) with a 1.2 m-aperture,0°.44 × 0°.44 field of view and 500 nm-900 nm working wave band.The camera focal plane is composed of a mosaic of 81 scientific CMOS detectors each with4 k × 4 k pixels.The heterodyne laser interferometric calibration technology is employed to ensure microarcsecond level(1 μas) relative astrometry precision to meet the requirements for detection of Earth-like planets.The CHES satellite operates at the Sun-Earth L2 point and observes all the target stars for 5 yr.CHES will offer the first direct measurements of true masses and inclinations of Earth Twins and super-Earths orbiting our neighbor stars based on microarcsecond astrometry from space.This will definitely enhance our understanding of the formation of diverse nearby planetary systems and the emergence of other worlds for solar-type stars,and finally provide insights to the evolution of our own solar system.

Simulating the Escaping Atmosphere of GJ 436 b with Two-fluid Magnetohydrodynamic Models

Observations of transmission spectra reveal that hot Jupiters and Neptunes are likely to possess escaping atmospheres driven by stellar radiation.Numerous models predict that magnetic fields may exert significant influences on the atmospheres of hot planets.Generally,the escaping atmospheres are not entirely ionized,and magnetic fields only directly affect the escape of ionized components within them.Considering the chemical reactions between ionized components and neutral atoms,as well as collision processes,magnetic fields indirectly impact the escape of neutral atoms,thereby influencing the detection signals of planetary atmospheres in transmission spectra.In order to simulate this process,we developed a magnetohydrodynamic multi-fluid model based on MHD code PLUTO.As an initial exploration,we investigated the impact of magnetic fields on the decoupling of H^(+)and H in the escaping atmosphere of the hot Neptune GJ436b.Due to the strong resonant interactions between H and H^(+),the coupling between them is tight even if the magnetic field is strong.Of course,alternatively,our work also suggests that merging H and H^(+)into a single flow can be a reasonable assumption in MHD simulations of escaping atmospheres.However,our simulation results indicate that under the influence of magnetic fields,there are noticeable regional differences in the decoupling of H^(+)and H.With the increase of magnetic field strength,the degree of decoupling also increases.For heavier particles such as O,the decoupling between O and H^(+)is more pronounced.Our findings provide important insights for future studies on the decoupling processes of heavy atoms in the escaping atmospheres of hot Jupiters and hot Neptunes under the influence of magnetic fields.

Strong Spatial Aggregation of Martian Surface Temperature Shaped by Spatial and Seasonal Variations in Meteorological and Environmental Factors

Spatio-temporal variation in the Martian surface temperature(MST)is an indicator of ground level thermal processes and hence a building block for climate models.However,the distribution of MST exhibits different levels of spatial aggregation or heterogeneity,and varies in space and time.Furthermore,the effect of regional differences in meteorological or environmental factors on the MST is not well understood.Thus,we investigated the degree of spatial autocorrelation of MST across the surface of Mars globally by Moran’s I,and identified the hot spots by GetisOrd G;*.We also estimated the regional differences in the influence of seasonally dominant factors including thermal inertia(TI),albedo,surface pressure,latitude,dust and slope on MST by a geographically weighted regression model.The results indicate(1)that MST is spatially aggregated and hot and cold spots varied over time and space.(2)Hemispheric differences in topography,surface TI and albedo were primarily responsible for the hemispheric asymmetry of hot spots.(3)The dominant factors varied by geographical locations and seasons.For example,the seasonal Hadley circulation dominates at the low-latitudes and CO;circulation at the high-latitudes.(4)Regions with extreme variations in topography and low TI were sensitive to meteorological and environmental factors such as dust and CO_(2)ice.We conclude that the spatial autocorrelation of MST and the spatial and seasonal heterogeneity of influencing factors must be considered when simulating Martian climate models.This work provides a reference for further exploration of Martian climatic processes.

A physical interpretation of the Titius-Bode rule and its connection to the closed orbits of Bertrand's theorem

We consider the geometric Titius-Bode rule for the semimajor axes of planetary orbits. We derive an equivalent rule for the midpoints of the segments between consecutive orbits along the radial direction and we interpret it physically in terms of the work done in the gravitational field of the Sun by particles whose orbits are perturbed around each planetary orbit. On such energetic grounds, it is not surprising that some exoplanets in multiple-planet extrasolar systems obey the same relation. However,it is surprising that this simple interpretation of the Titius-Bode rule also reveals new properties of the bound closed orbits predicted by Bertrand’s theorem, which has been known since 1873.

From Solar System to Exoplanets:What can we learn from Planetary Spectroscopy?

The purpose of this paper is to address the question:Using our knowledge of infrared planetary spectroscopy,what can we learn about the atmospheres of exoplanets?In a first part,a simplified classification of exoplanets,assuming thermochemical equilibrium,is presented,based on their masses and their equilibrium temperatures,in order to propose some possible estimations about their atmospheric composition.In the second part,infrared spectra of planets are discussed,in order to see what lessons can be drawn for exoplanetary spectroscopy.In the last part,we consider the solar system as it would appear from a star located in the ecliptic plane.It first appears that the solar system(except in a few specific cases)would not be seen as a multiple system,because,contrary to many exoplanetary systems,the planets are too far from the Sun and the inclinations of their orbits with respect to the ecliptic plane are too high.Primary transit synthetic spectra of solar system planets are used to discuss the relative merits of transmission and direct emission spectroscopy for probing exoplanetary atmospheres.