Exoplanets number in their thousands, and the number is ever increasing with the advent of new surveys and improved instrumentation. One of the most surprising things we have learnt from these discoveries is not that small-rocky planets in their stars habitable zones are likely common, but that the most typical size of exoplanet is that not seen in our solar system - radii between that of Neptune and the Earth dubbed mini-Neptunes and super-Earths. In fact, a transiting exoplanet is four times as likely to be in this size regime than that of any giant planet in our solar system. Investigations into the atmospheres of giant hydrogen/helium dominated exoplanets has pushed down to Neptune and mini-Neptune sized worlds revealing molecular absorption from water, scattering and opacity from clouds, and measurements of atmospheric abundances. However, unlike measurements of Jupiter, or even Saturn sized worlds, the smaller giants lack a ground truth on what to expect or interpret from their measurements. How did these sized worlds form and evolve and was it different from their larger counterparts? What is their internal composition and how does that impact their atmosphere? What informs the energy budget of these distant worlds? In this we discuss what characteristics we can measure for exoplanets, and why a mission to the ice giants in our solar system is the logical next step for understanding exoplanets.
Habitability of exoplanet's deepest oceans could be limited by the presence of high-pressure ices at their base. New work demonstrates that efficient chemical transport within deep planetary ice mantles is possible through significant salt incorporation within the high-pressure ice.
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…
A Recommendation Algorithm to Predict Giant Exoplanet Host Stars Using Stellar Elemental Abundances
恒星中某些元素的存在，以及其行星的存在，强烈影响着行星系的形成和演化。主恒星的铁含量与巨型系外行星的存在之间的正相关性已经得到证实;然而，其他元素在预测巨型行星出现方面的重要性却不那么确定，尽管它们在塑造行星内部结构方面发挥着核心作用。我们设计了一种机器学习算法，并将其应用于Hypatia目录（Hinkel et a. 2014年）分析已知宿主恒星的恒星丰度模式，以确定那些对识别潜在的巨型系外行星宿主恒星很重要的元素。我们分析了各种不同的元素组合，即挥发物，亲石，亲铁，和铁。我们发现，除了铁之外，氧，碳和钠的相对丰度是巨行星存在的有影响力的指标。我们通过分析具有已知巨行星的恒星来展示我们算法的预测能力，并发现它们的预测得分中值为75%。我们提出了一个列表，其中有350颗恒星目前还没有发现行星，它们有$\geq$ 90%的预测概率可能拥有一颗巨大的系外行星。我们研究了档案HARPS数据，发现HIP 62345，HIP 71803和HIP 10278主机长周期巨行星的同伴估计最小$M_p\sin(i)$值分别为3.7，6.8和8.5 M $_{J}$的显着趋势。我们预计，我们的发现将彻底改变未来的目标选择，元素在巨行星形成中的作用，以及巨行星内部结构模型的确定。
Photochemical Production of CS2 in Temperate-to-Warm Gas Giant Exoplanet Atmospheres
University of Chicago（芝加哥大学）；Arizona State University（亚利桑那州立大学）；University of California, Santa Cruz（加州大学圣克鲁兹分校）；Carnegie Institution for Science（卡内基科学机构）
A Search for Exoplanets around Northern Circumpolar Stars. IV. Six Planet Candidates to the K Giants, HD 44385, HD 97619, HD 106574, HD 118904, HD 164428, and HD 202432
The alkali metal sodium (Na) is one of the most commonly detected chemical species in the upper atmospheres of giant exoplanets. In this work we conducted a homogeneous survey of Na in a diverse sample of ten highly irradiated giant exoplanets using high-resolution transmission spectroscopy. Our sample includes nine planets with previous Na detections and one new detection. We confirm previous detections and assess multiple approaches for deriving Na line properties from high-resolution transmission spectra. The homogeneously measured sodium line depths were used to constrain the atmospheric h…
Ice giants are the only unexplored class of planet in our Solar System. Much that we currently know about these systems challenges our understanding of how planets, rings, satellites, and magnetospheres form and evolve. We assert that an ice giant Flagship mission with an atmospheric probe should be a priority for the decade 2023-2032.
Aims. We report the detection of long-period radial velocity (RV) variations in three giant stars, HD 19615, HD 150010, and HD 174205, using precise RV measurements. Methods. These detections are part of the Search for Exoplanets around Northern Circumpolar Stars (SENS) survey being conducted at the Bohyunsan Optical Astronomy Observatory (BOAO). The nature of the RV variations was investigated by analyzing the photometric and line shape variations. We found no variability with the RV period in these quantities and conclude that the RV variations are most likely caused by planetary companions.…
The Formation of Uranus and Neptune in Solid-Rich Feeding Zones: Connecting Chemistry and Dynamics
行星形成的核心吸积理论至少有两个基本问题来解释天王星和海王星的起源：（1）跨土星太阳星云的动力学时间很长，核心的增长可能需要超过1500万年，（2）当核心达到10个地球质量时，失控的气体吸积开始发生，这就需要在冰巨人核心达到临界质量时突然停止气体吸积。这两个问题都可以通过允许冰巨星在富含固体的供给区形成后向外迁移来解决，这些供给区的星子表面密度远高于最小质量的太阳星云。我们使用Nice模型（Gomes et al. 2005; Morbidelli et al. 2005; Tsiganis et al. 2005）的初始半长轴分布，对Dodson-Robinson et al.（2009）的富固体盘中天王星和海王星的形成进行了新的模拟，其中一个冰巨星在12 AU形成，另一个在15 AU形成。最里面的冰巨星在380万~ 400万年后达到现在的质量，最外面的冰巨星在530万~ 600万年后达到现在的质量，与以前的一维模拟相比，时间缩短了很多（例如Pollack et al. 1996）。核心质量保持亚临界状态，消除了突然停止气体吸积的需要。我们计算的碳质量分数为22%，与Podolak等人（1995）和Marley等人（1995）的冰巨星内部模型非常一致。基于形成冰巨星的微行星含有>10%质量分数的甲烷冰的要求，我们可以拒绝任何最初将天王星和海王星置于土星轨道内的太阳系形成模型。我们…
Exomoons represent a crucial missing puzzle piece in our efforts to understand extrasolar planetary systems. To address this deficiency, we here describe an exomoon survey of 70 cool, giant transiting exoplanet candidates found by Kepler. We identify only one which exhibits a moon-like signal that passes a battery of vetting tests: Kepler-1708 b. We show that Kepler-1708 b is a statistically validated Jupiter-sized planet orbiting a Sun-like quiescent star at ~1.6AU. The signal of the exomoon candidate, Kepler-1708 b-i, is a 4.8-sigma effect and is persistent across different instrumental detr…
Among exoplanets, the small-size population constitutes the dominant one, with a diversity of properties and compositions ranging from rocky to gas dominated envelope. While a large fraction of them have masses and radii similar to or smaller than Neptune, yet none share common properties in term of orbital period and insulation with our ice giants. These exoplanets belong to multi-planet systems where planets are closely packed within the first tenth of AU and often exposed to strong irradiation from their host star. Their formation process, subsequent evolution, and fate are still debated an…
We used high-precision radial velocity measurements of FGKM stars to determine the occurrence of giant planets as a function of orbital separation spanning 0.03-30 au. Giant planets are more prevalent at orbital distances of 1-10 au compared to orbits interior or exterior of this range. The increase in planet occurrence at $\sim$1 au by a factor of $\sim$4 is highly statistically significant. A fall-off in giant planet occurrence at larger orbital distances is favored over models with flat or increasing occurrence. We measure $14.1^{+2.0}_{-1.8}$ giant planets per 100 stars with semi-major axe…
Despite the severe bias of the transit method of exoplanet discovery toward short orbital periods, a modest sample of transiting exoplanets with orbital periods greater than 100 days is known. Long-term radial velocity (RV) surveys are pivotal to confirming these signals and generating a set of planetary masses and densities for planets receiving moderate to low irradiation from their host stars. Here, we conduct RV observations of Kepler-1514 from the Keck I telescope using the High Resolution Echelle Spectrometer. From these data, we measure the mass of the statistically validated giant ($1.…
