Terrestrial planets have been found orbiting Sun-like stars with extremely short periods --- some as short as 4 hours. These "ultra-short-period planets" or "hot Earths" are so strongly irradiated that any initial H/He atmosphere has probably been lost to photoevaporation. As such, the sample of hot Earths may give us a glimpse at the rocky cores that are often enshrouded by thick H/He envelopes on wider-orbiting planets. However, the mass and radius measurements of hot Earths have been derived from a hodgepodge of different modeling approaches, and include several cases of contradictory results. Here, we perform a homogeneous analysis of the complete sample of 11 known hot Earths with an insolation exceeding 650 times that of the Earth. We combine all available data for each planet, incorporate parallax information from {\it Gaia} to improve the stellar and planetary parameters, and use Gaussian Process regression to account for correlated noise in the radial-velocity data. The homogeneous analysis leads to a smaller dispersion in the apparent composition of hot Earths, although there does still appear to be some intrinsic dispersion. Most of the planets are consistent with an Earth-like composition (35\% iron and 65\% rock), but two planets (K2-141b and K2-229b) show evidence for a higher iron fraction, and one planet (55\,Cnc\,e) has either a very low iron fraction or an envelope of low-density volatiles. All of the planets are less massive than 8\,$M_\oplus$, despite the selection bias towards more massive planets, suggesting that 8\,$M_\oplus$ is the critical mass for runaway accretion.
We show that in extremely irradiated atmospheres of hot super-Earths shortwave absorption of CN can cause strong temperature inversions. We base this study on previous observations of 55 Cancri e, which lead us to believe that ultra-short-period super-Earths can sustain volatile atmospheres, rich in nitrogen and/or carbon. We compute our model atmospheres in a radiative-convective equilibrium for a variety of nitrogen-rich cases and orbital parameters. We demonstrate the effects caused by thermal inversions on the chemistry and compute low resolution synthetic emission spectra for a range of 0…
现在已知，大小介于地球（半径为R $_\oplus$）和海王星（半径约为4 R $_\oplus$）之间的行星在类太阳恒星周围很常见。大多数这样的行星都是通过凌日技术发现的，通过凌日技术，行星的大小可以从行星经过其恒星前时被行星阻挡的星光的比例来确定。测量这颗行星的质量以及它的密度（这是了解其组成的一个线索）则更为困难。大小为2-4 R $_\oplus$的行星已被证明具有广泛的密度范围，这意味着组成的多样性，但这些测量并没有延伸到像地球这样小的行星。在这里，我们报告了对地球大小的行星开普勒-78b质量的多普勒光谱测量，该行星每8.5小时绕其宿主恒星运行一次。假设半径为1.20 $\pm$ 0.09 R $_\oplus$，质量为1.69 $\pm$ 0.41 M $_\oplus$，行星的平均密度为5.3 $\pm$ 1.8 g cm $^{-3}$，与地球相似，表明它由岩石和铁组成。
At least 30\% of main sequence stars host planets with sizes of between 1 and 4 Earth radii and orbital periods of less than 100 days. We use N-body simulations including a model for gas-assisted pebble accretion and disk--planet tidal interaction to study the formation of super-Earth systems. We show that the integrated pebble mass reservoir creates a bifurcation between hot super-Earths or hot-Neptunes ($\lesssim15M_{\oplus}$) and super-massive planetary cores potentially able to become gas giant planets ($\gtrsim15M_{\oplus}$). Simulations with moderate pebble fluxes grow multiple super-Ear…
Observations have confirmed the existence of multiple-planet systems containing a hot Jupiter and smaller planetary companions. Examples include WASP-47, Kepler-730, and TOI-1130. We examine the plausibility of forming such systems in situ using $N$-body simulations that include a realistic treatment of collisions, an evolving protoplanetary disc and eccentricity/inclination damping of planetary embryos. Initial conditions are constructed using two different models for the core of the giant planet: a 'seed-model' and an 'equal-mass-model'. The former has a more massive protoplanet placed among…
最近的{ \em Kepler}观测显示，在$0.02-0.2$ AU的内部，有大量的地球大小到海王星大小的“热”行星。我们认为，这些较小的行星是大质量巨行星的残余物，它们向内迁移的速度比它们收缩的速度要快。我们表明，这种破坏自然发生在行星形成的潮汐缩小假说的框架。我们发现，这种“热破裂”发生的特征行星-恒星分离是$R \approx 0.03-0.2$ AU。这个结果与行星的胚胎质量无关，但取决于圆盘中的吸积速率。在高增长率下，$\dot M \simgt 10^{-6}\msun$ yr $^{-1}$，胚胎不能足够快地收缩并被破坏。在后期，当生长速率下降到$\dot M \simlt 10^{-8} \msun$ yr $^{-1}$时，胚胎迁移足够慢而不被破坏。这些“迟到者”也许可以解释众所周知的热木星人口。如果I型迁移机制效率低下，那么我们的模型预测，当迁移率突然从II型转换到I型时，在$R\sim 0.1$ AU处会有行星堆积。
The chemical compositions of Earth's core and mantle provide insight into the processes that led to their formation. N-body simulations, on the other hand, generally do not contain chemical information, and seek to only reproduce the masses and orbits of the terrestrial planets. These simulations can be grouped into four potentially viable scenarios of Solar System formation (Classical, Annulus, Grand Tack, and Early Instability) for which we compile a total of 433 N-body simulations. We relate the outputs of these simulations to the chemistry of Earth's core and mantle using a melt-scaling la…
The emergent spectra of close-in, giant exoplanets ("hot Jupiters") are expected to be distinct from those of self-luminous objects with similar effective temperatures because hot Jupiters are primarily heated from above by their host stars rather than internally from the release of energy from their formation. Theoretical models predict a continuum of dayside spectra for hot Jupiters as a function of irradiation level, with the coolest planets having absorption features in their spectra, intermediate-temperature planets having emission features due to thermal inversions, and the hottest plane…
Clouds in Super-Earth Atmospheres: Chemical Equilibrium Calculations
最近的研究已经明确证明了云在超级地球大气中的存在（Kreidberg et al. 2014）。在这里，我们提供了一个理论背景下形成的超级地球云，确定冷凝物可能形成的假设下的化学平衡。我们研究了不同体积成分的超级地球大气，这些大气被认为是由固体核心的南极物质放气形成的，遵循Schaefer和Fegley（2010）。我们所研究的超级地球大气层来自于由个别类型的南极陨石组成的行星核心。它们的范围从高度还原到氧化，并且具有太阳下和太阳上的碳氧比（C：O），从而跨越了适合低质量系外行星的大气成分范围。考虑到这些大气的原子组成，我们最小化了超过550种气体和冷凝物的全球吉布斯自由能，以获得350- 3000 K温度范围内大气的分子组成。在我们的计算中，云应该沿着出现凝聚物质的温度-压力边界形成。我们发现，凝结云的组成强烈地依赖于H：O和C：O的比例。对于超级地球原型GJ 1214 b，KCl和ZnS是太阳组成的主要云形成冷凝物，与先前的工作一致（Morley et al. 2013; Miller-Ricci Kempton et al. 2012）。然而，对于氧化性大气，K2 SO 4和ZnO冷凝物是有利的，而对于具有超太阳C：O比率的富碳大气，石墨云出现。对于更热的行星，云是由各种各样的岩石和金属物质形成的。
Hot and cloudy: High temperature clouds in super-Earths and sub-Neptunes
Leiden Observatory（莱顿天文台）；SRON Netherlands Institute for Space Research（荷兰空间研究所）；Tsinghua University（清华大学）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）
Aerosols are common in the atmospheres of exoplanets across a wide swath of temperatures, masses, and ages. These aerosols strongly impact observations of transmitted, reflected, and emitted light from exoplanets, obfuscating our understanding of exoplanet thermal structure and composition. Knowing the dominant aerosol composition would facilitate interpretations of exoplanet observations and theoretical understanding of their atmospheres. A variety of compositions have been proposed, including metal oxides and sulphides, iron, chromium, sulphur, and hydrocarbons. However, the relative contrib…
Impact-induced erosion of the Earth's early crust during accretion of terrestrial bodies can significantly modify the primordial chemical composition of the Bulk Silicate Earth (BSE, that is, the composition of the crust added to the present-day mantle). In particular, it can be particularly efficient in altering the abundances of elements having a strong affinity for silicate melts (i.e. incompatible elements) as the early differentiated crust was preferentially enriched in those. Here, we further develop an erosion model (EROD) to quantify the effects of collisional erosion on the final comp…
Composition and Space Weathering Characteristics of Tianwen-2 Mission's First Target Near-Earth Asteroid (469219) Kamo`oalewa
National Space Science Center, Chinese Academy of Sciences（中国科学院国家空间科学中心）；University of Chinese Academy of Science（中国科学院大学）；Sun Yat-sen University（中山大学）；Xinjiang Astronomical Observatory, Chinese Academy of Sciences（中国科学院新疆天文台）；Shandong University（山东大学）
The day and nightside temperatures of hot Jupiters are diagnostic of heat transport processes in their atmospheres. Recent observations have shown that the nightsides of hot Jupiters are a nearly constant 1100 K for a wide range of equilibrium temperatures (T$_{eq}$), lower than those predicted by 3D global circulation models. Here we investigate the impact of nightside clouds on the observed nightside temperatures of hot Jupiters using an aerosol microphysics model. We find that silicates dominate the cloud composition, forming an optically thick cloud deck on the nightsides of all hot Jupite…
Earth is depleted in volatile elements relative to chondritic meteorites, its possible building blocks. The extent of this depletion increases with decreasing condensation temperature, and is approximated by a cumulative normal distribution, unlike that in any chondrite. However, moderately volatile elements, occupying the mid-range of the distribution, have chondritic isotope ratios, contrary to that expected from loss by partial vaporisation/condensation. Here we reconcile these observations by showing, using N-body simulations, that Earth accreted stochastically from many precursor bodies w…
