The best constraints on the internal structures of giant planets have historically come from measurements of their gravity fields. These gravity data are inherently mostly sensitive to a planet's outer regions, providing only loose constraints on the deep interiors of Jupiter and Saturn. This fundamental limitation stymies efforts to measure the mass and compactness of these planets' cores, crucial properties for understanding their formation pathways and evolution. However, studies of Saturn's rings have revealed waves driven by pulsation modes within Saturn, offering independent seismic probes of Saturn's interior. The observations reveal gravity mode (g mode) pulsations which indicate that a part of Saturn's interior is stably stratified by composition gradients, and the g mode frequencies directly probe the buoyancy frequency within the planet. Here, we compare structural models with gravity and seismic measurements to show that the data can only be explained by a diffuse, stably stratified core-envelope transition region in Saturn extending to approximately 60% of the planet's radius and containing approximately 17 Earth masses of ice and rock. The gradual distribution of heavy elements constrains mixing processes at work in Saturn, and it may reflect the planet's primordial structure and accretion history.
Saturn's Evolutionary History and Seismology: Survival of Deep Stably Stratified Regions in Evolutionary Models of Saturn Consistent with Ring Seismology
Princeton University（普林斯顿大学）；Canadian Institute for Theoretical Astrophysics, University of Toronto（多伦多大学加拿大理论天体物理研究所）；University of Massachusetts Amherst（马萨诸塞大学阿默斯特分校）；University of California Los Angeles（加州大学洛杉矶分校）
Excitation and Damping of Oscillation Modes in Gaseous Planets
California Institute of Technology（加州理工学院）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；New Mexico State University（新墨西哥州立大学）
Incomplete cooling down of Saturn's A ring at solar equinox: Implication for seasonal thermal inertia and internal structure of ring particles
在2009年8月的太阳分点，卡西尼号上的复合红外光谱仪（CIRS）显示了有史以来观测到的最低土星环温度。详细的辐射转移模型表明，只要只考虑土星的通量，土星A环观测到的春分温度就比模型预测的要高得多。这表明A环在春分点没有完全冷却下来。我们开发了一个简单的季节性环温度模型，并首先假设环颗粒的内部密度和热惯性是均匀的深度。颗粒大小估计为1-2 μ m。A环中部的季节热惯量为30-50 JmPDMATHABMM K $^{-1}$ s $^{-1/2}$，而A环内外区的季节热惯量为10 JmPDMATHABMM K $^{-1}$ s $^{-1/2}$或与昼夜热惯量一样低。一个附加的内部结构模型，其中一个粒子有一个高密度的核心周围的蓬松的风化层地幔，表明核心半径相对于粒子半径约为0.9的中间A环和更小的内部和外部区域的A环。这意味着环粒子内部密度的径向变化存在于整个A环。一些机制可能是将致密颗粒限制在中间A环中以防止粘性扩散。或者，（中间的）A环可能是最近（$<$ 10 $^{8}$ yr）由于一颗冰冷的卫星的破坏而形成的，因此致密的颗粒还没有扩散到A环上，颗粒的风化层地幔还没有变厚。我们的模型结果还表明，核心的成分主要是水冰，而不是岩石。
High-Energy Neutrino Tomography of the Earth's Interior with IceCube
Loyola University Chicago（洛约拉大学芝加哥分校）；Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器）；University of Canterbury（坎特伯雷大学）；Université Libre de Bruxelles（布鲁塞尔自由大学）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；TU Dortmund University（多特蒙德工业大学）；University of Kansas（堪萨斯大学）；Bartol Research Institute and Dept. of Physics and Astronomy, University of Delaware（特拉华大学巴托尔研究所及物理与天文学系）；Marquette University（马凯特大学）；Harvard University（哈佛大学）；Michigan State University（密歇根州立大学）；South Dakota School of Mines and Technology（南达科他矿业理工学院）
