247 research outputs found
Models of Saturn's Interior Constructed with Accelerated Concentric Maclaurin Spheroid Method
The Cassini spacecraft's Grand Finale orbits provided a unique opportunity to
probe Saturn's gravity field and interior structure. Doppler measurements
yielded unexpectedly large values for the gravity harmonics J_6, J_8, and J_10
that cannot be matched with planetary interior models that assume uniform
rotation. Instead we present a suite of models that assume the planet's
interior rotates on cylinders, which allows us to match all the observed even
gravity harmonics. For every interior model, the gravity field is calculated
self-consistently with high precision using the Concentric Maclaurin Spheroid
(CMS) method. We present an acceleration technique for this method, which
drastically reduces the computational cost, allows us to efficiently optimize
model parameters, map out allowed parameter regions with Monte Carlo sampling,
and increases the precision of the calculated J_2n gravity harmonics to match
the error bars of the observations, which would be difficult without
acceleration. Based on our models, Saturn is predicted to have a dense central
core of 15-18 Earth masses and an additional 1.5-5 Earth masses of heavy
elements in the envelope. Finally, we vary the rotation period in the planet's
deep interior and determine the resulting oblateness, which we compare with the
value from radio occultation measurements by the Voyager spacecraft. We predict
a rotation period of 10:33:34 h +- 55s, which is in agreement with recent
estimates derived from ring seismology.Comment: 12 color figures, 5 tables, Astrophysical Journal, in press (2019
Sequestration of noble gases in giant planet interiors
The Galileo probe showed that Jupiter's atmosphere is severely depleted in
neon compared to protosolar values. We show, via ab initio simulations of the
partitioning of neon between hydrogen and helium phases, that the observed
depletion can be explained by the sequestration of neon into helium-rich
droplets within the postulated hydrogen-helium immiscibility layer of the
planet's interior. We also demonstrate that this mechanism will not affect
argon, explaining the observed lack of depletion of this gas. This provides
strong indirect evidence for hydrogen-helium immiscibility in Jupiter
Structure and bonding of dense liquid oxygen from first principles simulations
Using first principles simulations we have investigated the structural and
bonding properties of dense fluid oxygen up to 180 GPa. We have found that band
gap closure occurs in the molecular liquid, with a "slow" transition from a
semi-conducting to a poor metallic state occurring over a wide pressure range.
At approximately 80 GPa, molecular dissociation is observed in the metallic
fluid. Spin fluctuations play a key role in determining the electronic
structure of the low pressure fluid, while they are suppressed at high
pressure.Comment: 4 figure
Hydrogen-Helium Mixtures in the Interiors of Giant Planets
Equilibrium properties of hydrogen-helium mixtures under conditions similar
to the interior of giant gas planets are studied by means of first principle
density functional molecular dynamics simulations. We investigate the molecular
and atomic fluid phase of hydrogen with and without the presence of helium for
densities between gcm and gcm and
temperatures from K to . Helium has a crucial influence on
the ionic and electronic structure of the liquid. Hydrogen molecule bonds are
shortened as well as strengthened which leads to more stable hydrogen molecules
compared to pure hydrogen for the same thermodynamic conditions. The {\it ab
initio} treatment of the mixture enables us to investigate the validity of the
widely used linear mixing approximation. We find deviations of up to 8% in
energy and volume from linear mixing at constant pressure in the region of
molecular dissociation.Comment: 13 pages, 18 figures, submitted to PR
Hydrogen-Helium Mixtures at High Pressure
The properties of hydrogen-helium mixtures at high pressure are crucial to
address important questions about the interior of Giant planets e.g. whether
Jupiter has a rocky core and did it emerge via core accretion? Using path
integral Monte Carlo simulations, we study the properties of these mixtures as
a function of temperature, density and composition. The equation of state is
calculated and compared to chemical models. We probe the accuracy of the ideal
mixing approximation commonly used in such models. Finally, we discuss the
structure of the liquid in terms of pair correlation functions.Comment: Proceedings article of the 5th Conference on Cryocrystals and Quantum
Crystals in Wroclaw, Poland, submitted to J. Low. Temp. Phys. (2004
Calculation of a Deuterium Double Shock Hugoniot from Ab initio Simulations
We calculate the equation of state of dense deuterium with two ab initio
simulations techniques, path integral Monte Carlo and density functional theory
molecular dynamics, in the density range of 0.67 < rho < 1.60 g/cc. We derive
the double shock Hugoniot and compare with the recent laser-driven double shock
wave experiments by Mostovych et al. [1]. We find excellent agreement between
the two types of microscopic simulations but a significant discrepancy with the
laser-driven shock measurements.Comment: accept for publication in Phys. Rev. Lett., Nov. 2001, 4 pages, 4
figure
Mass-Radius Relationships for Solid Exoplanets
We use new interior models of cold planets to investigate the mass-radius
relationships of solid exoplanets, considering planets made primarily of iron,
silicates, water, and carbon compounds. We find that the mass-radius
relationships for cold terrestrial-mass planets of all compositions we
considered follow a generic functional form that is not a simple power law:
for up to , where and are scaled mass and radius
values. This functional form arises because the common building blocks of solid
planets all have equations of state that are well approximated by a modified
polytrope of the form .
We find that highly detailed planet interior models, including temperature
structure and phase changes, are not necessary to derive solid exoplanet bulk
composition from mass and radius measurements. For solid exoplanets with no
substantial atmosphere we have also found that: with 5% fractional uncertainty
in planet mass and radius it is possible to distinguish among planets composed
predominantly of iron or silicates or water ice but not more detailed
compositions; with ~5% uncertainty water ice planets with
water by mass may be identified; the minimum plausible planet size for a given
mass is that of a pure iron planet; and carbon planet mass-radius relationships
overlap with those of silicate and water planets due to similar zero-pressure
densities and equations of state. We propose a definition of "super Earths''
based on the clear distinction in radii between planets with significant gas
envelopes and those without.Comment: ApJ, in press, 33 pages including 16 figure
The effect of differential rotation on Jupiter's low-degree even gravity moments
The close-by orbits of the ongoing Juno mission allow measuring with unprecedented accuracy Jupiter's low-degree even gravity moments J(2), J(4), J(6), and J(8). These can be used to better determine Jupiter's internal density profile and constrain its core mass. Yet the largest unknown on these gravity moments comes from the effect of differential rotation, which gives a degree of freedom unaccounted for by internal structure models. Here considering a wide range of possible internal flow structures and dynamical considerations, we provide upper bounds to the effect of dynamics (differential rotation) on the low-degree gravity moments. In light of the recent Juno gravity measurements and their small uncertainties, this allows differentiating between the various models suggested for Jupiter's internal structure.Israeli Ministry of Science; Minerva foundation; Federal German Ministry of Education and Research; Helen Kimmel Center for Planetary Science at the Weizmann Institute of Science; CNES; BSF; NSF; Juno project6 month embargo; Published Online: 19 June 2017This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Evolution of austenite recrystallization and grain growth using laser-ultrasonics
Peer reviewed: YesNRC publication: Ye
- …