scholarly journals Internal Structure of Giant and Icy Planets: Importance of Heavy Elements and Mixing

2017 ◽  
pp. 1-19
Author(s):  
Ravit Helled ◽  
Tristan Guillot
Keyword(s):  
Internal Structure ◽  
Heavy Elements

scholarly journals Exploration of the structure of giant planets with fast calculations and a bayesian approach

2021 ◽  
Author(s):  
Saburo Howard ◽  
Tristan Guillot ◽  
Michaël Bazot ◽  
Yamila Miguel
Keyword(s):  
Gravity Field ◽  
Internal Structure ◽  
Bayesian Approach ◽  
Equations Of State ◽  
Giant Planets ◽  
Heavy Elements ◽  
Fast Method ◽  
Metallic Hydrogen ◽  
Chemical Abundances ◽  
Wide Range

<p><strong>Abstract</strong></p> <p>The Juno spacecraft is providing measurements of Jupiter's gravity field with an outstanding level of accuracy [3], leading to better constraints on the interior of Jupiter. Improving our knowledge of the internal structure of Jupiter is key, to understand the formation and the evolution of the planet [5,6] but also in the framework of exoplanets exploration. Hence, developing interiors models of Jupiter which are consistent with the observations is essential.</p> <p>Models of giant planets' internal structure are built with the code CEPAM [2] to compute the gravitational moments <em>J<sub>2n</sub></em> [1] and compare them to the observational values. As the numerical calculation of the gravitational moments is crucial, we are here using a fast method based on a 4th order development of the Theory of Figures, coupled with the more precise CMS (Concentric MacLaurin Spheroid) method. This allows us to obtain reliable values of <em>J<sub>2n</sub></em> in a reasonable amount of time.</p> <p>MCMC (Markov chain Monte Carlo) simulations are then run to study a wide range of interior models, using the above way to compute the gravitational moments. This bayesian approach leads to a broad investigation of the parameters range such as the chemical abundances, the 1 bar temperature or the transition pressure between the molecular hydrogen and metallic hydrogen layers.</p> <p>Important questions remain to be clarified like the distribution and amount of the heavy elements inside giant planets, following the hypothesis of a gradual distribution of the heavy elements up to a certain fraction of Jupiter's radius [7]. Throughout this talk, I will pay particular attention on the equations of state used in our models [4]. Indeed, giant planets' internal structure seems strongly linked to the physical properties of its components and it is critical to assess how sensitive to the equations of state our models are.</p> <p><strong>References</strong></p> <p>[1] Guillot, T., Miguel, Y. et al.: A suppression of differential rotation in Jupiter's deep interior, Nature, Vol 555, pp. 227-230, (2018).</p> <p>[2] Guillot, T. and Morel, P.: CEPAM: a code for modeling the interiors of giant planets, Astronomy and Astrophysics Supplement Series 109, 109-123 (1995)</p> <p>[3] Iess, L. et al.: Measurement of Jupiter's asymmetric gravity field, Nature, Vol 555, pp. 220-222, (2018).</p> <p>[4] Miguel, Y., Guillot, T. et al.: Jupiter internal structure: the effect of different equations of state. Astron. Astrophys. 596, A114 (2016)</p> <p>[5] Vazan, A., Helled, R. and Guillot, T.: Jupiter's evolution with primordial composition gradients. Astron. Astrophys. 610, L14 (2018).</p> <p>[6] Venturini, J., Helled, R.: Jupiter's heavy-element enrichment expected from formation models. Astron. Astrophys. 634, A31 (2020).</p> <p>[7] Wahl, S. M. et al.: Comparing Jupiter interior structure models to Juno gravity measurements and the role of a dilute core, Geophys. Res. Lett. Vol 44, pp. 4649-4659, (2017).</p>

scholarly journals The Interiors of Jupiter and Saturn

2019 ◽  
Author(s):  
Ravit Helled
Keyword(s):  
Internal Structure ◽  
High Pressures ◽  
Theoretical Models ◽  
Heavy Elements ◽  
Gravitational Fields ◽  
Deep Interior ◽  
The Masses ◽  
Two Envelopes ◽  
Heat Transport Mechanism ◽  
Alternative Structure

Probing the interiors of the gaseous giant planets in our solar system is not an easy task. It requires a set of accurate measurements combined with theoretical models that are used to infer the planetary composition and its depth dependence. The masses of Jupiter and Saturn are 317.83 and 95.16 Earth masses (M⊕), respectively, and since a few decades, it has been known that they mostly consist of hydrogen and helium. The mass of heavy elements (all elements heavier than helium) is not well determined, nor are their distribution within the planets. While the heavy elements are not the dominating materials inside Jupiter and Saturn, they are the key to understanding the planets’ formation and evolutionary histories. The planetary internal structure is inferred from theoretical models that fit the available observational constraints by using theoretical equations of states (EOSs) for hydrogen, helium, their mixtures, and heavier elements (typically rocks and/or ices). However, there is no unique solution for determining the planetary structure and the results depend on the used EOSs as well as the model assumptions imposed by the modeler. Major model assumptions that can affect the derived internal structure include the number of layers, the heat transport mechanism within the planet (and its entropy), the nature of the core (compact vs. diluted), and the location (pressure) of separation between the two envelopes. Alternative structure models assume a less distinct division between the layers and /or a non-homogenous distribution of the heavy elements. The fact that the behavior of hydrogen at high pressures and temperatures is not perfectly known and that helium may separate from hydrogen at the deep interior add sources of uncertainty to structure models. In the 21st century, with accurate measurements of the gravitational fields of Jupiter and Saturn from the Juno and Cassini missions, structure models can be further constrained. At the same time, these measurements introduce new challenges for planetary modelers.

Distribution of R- and S-Process Elements in the Galactic Halo

1988 ◽  
Vol 132 ◽  
pp. 501-506
Author(s):  
C. Sneden ◽  
C. A. Pilachowski ◽  
K. K. Gilroy ◽  
J. J. Cowan
Keyword(s):  
Heavy Element ◽  
Galactic Halo ◽  
Low Noise ◽  
Heavy Elements ◽  
Process Synthesis ◽  
Element Abundances ◽  
Halo Stars ◽  
Abundance Patterns ◽  
R Process ◽  
Process Elements

Current observational results for the abundances of the very heavy elements (Z>30) in Population II halo stars are reviewed. New high resolution, low noise spectra of many of these extremely metal-poor stars reveal general consistency in their overall abundance patterns. Below Galactic metallicities of [Fe/H] Ã −2, all of the very heavy elements were manufactured almost exclusively in r-process synthesis events. However, there is considerable star-to-star scatter in the overall level of very heavy element abundances, indicating the influence of local supernovas on element production in the very early, unmixed Galactic halo. The s-process appears to contribute substantially to stellar abundances only in stars more metal-rich than [Fe/H] Ã −2.

Scattering-angle dependence of signal/background ratio of inner-shell electron excitation loss in EELS

1983 ◽  
Vol 41 ◽  
pp. 390-391
Author(s):  
T. Oikawa ◽  
M. Inoue ◽  
T. Honda ◽  
Y. Kokubo
Keyword(s):  
Energy Loss ◽  
Electron Excitation ◽  
Heavy Elements ◽  
Background Intensity ◽  
Light Elements ◽  
Energy Analyzer ◽  
High Background ◽  
Scattering Angle ◽  
Angle Dependence ◽  
Shell Electron

EELS allows us to make analysis of light elements such as hydrogen to heavy elements of microareas on the specimen. In energy loss spectra, however, elemental signals ride on a high background; therefore, the signal/background (S/B) ratio is very low in EELS. A technique which collects the center beam axial-symmetrically in the scattering angle is generally used to obtain high total intensity. However, the technique collects high background intensity together with elemental signals; therefore, the technique does not improve the S/B ratio. This report presents the experimental results of the S/B ratio measured as a function of the scattering angle and shows the possibility of the S/B ratio being improved in the high scattering angle range.Energy loss spectra have been measured using a JEM-200CX TEM with an energy analyzer ASEA3 at 200 kV.Fig.l shows a typical K-shell electron excitation edge riding on background in an energy loss spectrum.

X-ray microtomography

1988 ◽  
Vol 46 ◽  
pp. 998-999
Author(s):  
H.W. Deckman ◽  
B.F. Flannery ◽  
J.H. Dunsmuir ◽  
K.D' Amico
Keyword(s):  
Computed Tomography ◽  
Internal Structure ◽  
Imaging Technique ◽  
Three Dimensional ◽  
Tissue Structure ◽  
Individual Element ◽  
X Ray ◽  
Non Invasive ◽  
Panoramic Imaging ◽  
Three Dimensional Images

We have developed a new X-ray microscope which produces complete three dimensional images of samples. The microscope operates by performing X-ray tomography with unprecedented resolution. Tomography is a non-invasive imaging technique that creates maps of the internal structure of samples from measurement of the attenuation of penetrating radiation. As conventionally practiced in medical Computed Tomography (CT), radiologists produce maps of bone and tissue structure in several planar sections that reveal features with 1mm resolution and 1% contrast. Microtomography extends the capability of CT in several ways. First, the resolution which approaches one micron, is one thousand times higher than that of the medical CT. Second, our approach acquires and analyses the data in a panoramic imaging format that directly produces three-dimensional maps in a series of contiguous stacked planes. Typical maps available today consist of three hundred planar sections each containing 512x512 pixels. Finally, and perhaps of most import scientifically, microtomography using a synchrotron X-ray source, allows us to generate maps of individual element.

The internal structure of medullated wool

1984 ◽  
Vol 42 ◽  
pp. 388-389
Author(s):  
Leo Barish
Keyword(s):  
Light Microscopy ◽  
Internal Structure ◽  
Wool Fiber ◽  
Guard Hair ◽  
Bright Field ◽  
Wool Fibers ◽  
Thin Skin ◽  
Air Pockets

Although most of the wool used today consists of fine, unmedullated down-type fibers, a great deal of coarse wool is used for carpets, tweeds, industrial fabrics, etc. Besides the obvious diameter difference, coarse wool fibers are often medullated.Medullation may be easily observed using bright field light microscopy. Fig. 1A shows a typical fine diameter nonmedullated wool fiber, Fig. IB illustrates a coarse fiber with a large medulla. The opacity of the medulla is due to the inability of the mounting media to penetrate to the center of the fiber leaving air pockets. Fig. 1C shows an even thicker fiber with a very large medulla and with very thin skin. This type of wool is called “Kemp”, is shed annually or more often, and corresponds to guard hair in fur-bearing animals.

Long-period modulated superstructures in Pd-12.5 at.%Ce and Pd-15 at.%Ce alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 164-165
Author(s):  
Noriyuki Kuwano ◽  
Masaru Itakura ◽  
Kensuke Oki
Keyword(s):  
Electron Microscopy ◽  
Mean Value ◽  
Heavy Elements ◽  
Arc Furnace ◽  
X Ray ◽  
Long Period ◽  
Ultra High Purity ◽  
Heat Treated ◽  
Atomic Scattering ◽  
The Mean

Pd-Ce alloys exhibit various anomalies in physical properties due to mixed valences of Ce, and the anomalies are thought to be strongly related with the crystal structures. Since Pd and Ce are both heavy elements, relative magnitudes of (fcc-fpd) are so small compared with <f> that superlattice reflections, even if any, sometimes cannot be detected in conventional x-ray powder patterns, where fee and fpd are atomic scattering factors of Ce and Pd, and <f> the mean value in the crystal. However, superlattices in Pd-Ce alloys can be analyzed by electron microscopy, thanks to the high detectability of electron diffraction. In this work, we investigated modulated superstructures in alloys with 12.5 and 15.0 at.%Ce.Ingots of Pd-Ce alloys were prepared in an arc furnace under atmosphere of ultra high purity argon. The disc specimens cut out from the ingots were heat-treated in vacuum and electrothinned to electron transparency by a jet method.

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