scholarly journals Measurement and implications of Saturn’s gravity field and ring mass

Science ◽  
2019 ◽  
Vol 364 (6445) ◽  
pp. eaat2965 ◽  
Author(s):  
L. Iess ◽  
B. Militzer ◽  
Y. Kaspi ◽  
P. Nicholson ◽  
D. Durante ◽  
...  
Keyword(s):  
Gravitational Field ◽  
Total Mass ◽  
Radio Link ◽  
Interior Structure ◽  
The Moon ◽  
Final Phase ◽  
Cassini Mission ◽  
Formation And Evolution ◽  
Cloud Tops ◽  
Innermost Ring

The interior structure of Saturn, the depth of its winds, and the mass and age of its rings constrain its formation and evolution. In the final phase of the Cassini mission, the spacecraft dived between the planet and its innermost ring, at altitudes of 2600 to 3900 kilometers above the cloud tops. During six of these crossings, a radio link with Earth was monitored to determine the gravitational field of the planet and the mass of its rings. We find that Saturn’s gravity deviates from theoretical expectations and requires differential rotation of the atmosphere extending to a depth of at least 9000 kilometers. The total mass of the rings is (1.54 ± 0.49) × 1019 kilograms (0.41 ± 0.13 times that of the moon Mimas), indicating that the rings may have formed 107 to 108 years ago.

scholarly journals Rock Location and Property Analysis of Lunar Regolith at Chang’E-4 Landing Site Based on Local Correlation and Semblance Analysis

2020 ◽  
Vol 13 (1) ◽  
pp. 48
Author(s):  
Hanjie Song ◽  
Chao Li ◽  
Jinhai Zhang ◽  
Xing Wu ◽  
Yang Liu ◽  
...  
Keyword(s):  
Electromagnetic Waves ◽  
Lunar Regolith ◽  
Landing Site ◽  
Rock Properties ◽  
The Moon ◽  
Local Correlation ◽  
Near Surface ◽  
Property Analysis ◽  
Stratigraphic Division ◽  
Formation And Evolution

The Lunar Penetrating Radar (LPR) onboard the Yutu-2 rover from China’s Chang’E-4 (CE-4) mission is used to probe the subsurface structure and the near-surface stratigraphic structure of the lunar regolith on the farside of the Moon. Structural analysis of regolith could provide abundant information on the formation and evolution of the Moon, in which the rock location and property analysis are the key procedures during the interpretation of LPR data. The subsurface velocity of electromagnetic waves is a vital parameter for stratigraphic division, rock location estimates, and calculating the rock properties in the interpretation of LPR data. In this paper, we propose a procedure that combines the regolith rock extraction technique based on local correlation between the two sets of LPR high-frequency channel data and the common offset semblance analysis to determine the velocity from LPR diffraction hyperbola. We consider the heterogeneity of the regolith and derive the relative permittivity distribution based on the rock extraction and semblance analysis. The numerical simulation results show that the procedure is able to obtain the high-precision position and properties of the rock. Furthermore, we apply this procedure to CE-4 LPR data and obtain preferable estimations of the rock locations and the properties of the lunar subsurface regolith.

scholarly journals Bayesian constraints on the origin and geology of exo-planetary material using a population of externally polluted white dwarfs

2021 ◽  
Author(s):  
John H D Harrison ◽  
Amy Bonsor ◽  
Mihkel Kama ◽  
Andrew M Buchan ◽  
Simon Blouin ◽  
...  
Keyword(s):  
Solar System ◽  
White Dwarf ◽  
Bayesian Model ◽  
Total Mass ◽  
White Dwarfs ◽  
Bulk Composition ◽  
Planetary Systems ◽  
The Moon ◽  
Planetary Bodies ◽  
Nearby Stars

Abstract White dwarfs that have accreted planetary bodies are a powerful probe of the bulk composition of exoplanetary material. In this paper, we present a Bayesian model to explain the abundances observed in the atmospheres of 202 DZ white dwarfs by considering the heating, geochemical differentiation, and collisional processes experienced by the planetary bodies accreted, as well as gravitational sinking. The majority (>60%) of systems are consistent with the accretion of primitive material. We attribute the small spread in refractory abundances observed to a similar spread in the initial planet-forming material, as seen in the compositions of nearby stars. A range in Na abundances in the pollutant material is attributed to a range in formation temperatures from below 1,000 K to higher than 1,400 K, suggesting that pollutant material arrives in white dwarf atmospheres from a variety of radial locations. We also find that Solar System-like differentiation is common place in exo-planetary systems. Extreme siderophile (Fe, Ni or Cr) abundances in 8 systems require the accretion of a core-rich fragment of a larger differentiated body to at least a 3σ significance, whilst one system shows evidence that it accreted a crust-rich fragment. In systems where the abundances suggest that accretion has finished (13/202), the total mass accreted can be calculated. The 13 systems are estimated to have accreted masses ranging from the mass of the Moon to half that of Vesta. Our analysis suggests that accretion continues for 11Myrs on average.

Shape of the Moon from the Orbiter Determination of its Gravitational Field

Nature ◽  
1966 ◽  
Vol 212 (5059) ◽  
pp. 271-271 ◽  
Author(s):  
C. L. GOUDAS ◽  
Z. KOPAL ◽  
Z. KOPAL
Keyword(s):  
Gravitational Field ◽  
The Moon

Saturn's Gravitational Field, Internal Rotation, and Interior Structure

Science ◽  
2007 ◽  
Vol 317 (5843) ◽  
pp. 1384-1387 ◽  
Author(s):  
J. D. Anderson ◽  
G. Schubert
Keyword(s):  
Gravitational Field ◽  
Internal Rotation ◽  
Interior Structure

scholarly journals Close Cassini flybys of Saturn’s ring moons Pan, Daphnis, Atlas, Pandora, and Epimetheus

Science ◽  
2019 ◽  
Vol 364 (6445) ◽  
pp. eaat2349 ◽  
Author(s):  
B. J. Buratti ◽  
P. C. Thomas ◽  
E. Roussos ◽  
C. Howett ◽  
M. Seiß ◽  
...  
Keyword(s):  
Optical Properties ◽  
Water Vapor ◽  
Thermal Infrared ◽  
Ring System ◽  
The Moon ◽  
Volcanic Plumes ◽  
Cassini Mission ◽  
Main Ring

Saturn’s main ring system is associated with a set of small moons that either are embedded within it or interact with the rings to alter their shape and composition. Five close flybys of the moons Pan, Daphnis, Atlas, Pandora, and Epimetheus were performed between December 2016 and April 2017 during the ring-grazing orbits of the Cassini mission. Data on the moons’ morphology, structure, particle environment, and composition were returned, along with images in the ultraviolet and thermal infrared. We find that the optical properties of the moons’ surfaces are determined by two competing processes: contamination by a red material formed in Saturn’s main ring system and accretion of bright icy particles or water vapor from volcanic plumes originating on the moon Enceladus.

The Gravity Field and Interior Structure of Enceladus

Science ◽  
2014 ◽  
Vol 344 (6179) ◽  
pp. 78-80 ◽  
Author(s):  
L. Iess ◽  
D. J. Stevenson ◽  
M. Parisi ◽  
D. Hemingway ◽  
R. A. Jacobson ◽  
...  
Keyword(s):  
Gravity Field ◽  
Polar Region ◽  
Hydrostatic Equilibrium ◽  
The Body ◽  
Interior Structure ◽  
Negative Mass ◽  
Cassini Mission ◽  
Doppler Data ◽  
The Moment ◽  
South Polar

The small and active Saturnian moon Enceladus is one of the primary targets of the Cassini mission. We determined the quadrupole gravity field of Enceladus and its hemispherical asymmetry using Doppler data from three spacecraft flybys. Our results indicate the presence of a negative mass anomaly in the south-polar region, largely compensated by a positive subsurface anomaly compatible with the presence of a regional subsurface sea at depths of 30 to 40 kilometers and extending up to south latitudes of about 50°. The estimated values for the largest quadrupole harmonic coefficients (106J2= 5435.2 ± 34.9, 106C22= 1549.8 ± 15.6, 1σ) and their ratio (J2/C22= 3.51 ± 0.05) indicate that the body deviates mildly from hydrostatic equilibrium. The moment of inertia is around 0.335MR2, whereMis the mass andRis the radius, suggesting a differentiated body with a low-density core.

scholarly journals Interior structure of the Moon: Constraints from seismic tomography, gravity and topography

2015 ◽  
Vol 245 ◽  
pp. 26-39 ◽  
Author(s):  
Bernhard Steinberger ◽  
Dapeng Zhao ◽  
Stephanie C. Werner
Keyword(s):  
Seismic Tomography ◽  
Interior Structure ◽  
The Moon

THE GRAVITOKINETIC FIELD AND THE ORBIT OF MERCURY

1966 ◽  
Vol 44 (5) ◽  
pp. 1147-1156 ◽  
Author(s):  
J. C. W. Scott
Keyword(s):  
Field Theory ◽  
Electromagnetic Field ◽  
Gravitational Field ◽  
Electromagnetic Force ◽  
Total Mass ◽  
Gravitational Force ◽  
Space Time ◽  
Red Shift ◽  
Null Results ◽  
Magnetic Components

A new Lorentz-invariant gravitational field theory is introduced according to which space–time is always flat. The gravitational field is of Maxwellian form with potential and kinetic components analogous to the electric and magnetic components of the electromagnetic field. New mathematical entities named scaled tensors are developed. While the electromagnetic force is represented by an unsealed tensor, the gravitational force is properly described by a scaled tensor. The precession of the orbit of the planet Mercury establishes the scale of the gravitational force as −5. Since the force on a body is found to be proportional to its total mass, the null results of Eötvös and Dicke are confirmed. However, the theory requires that the force depend on velocity so that new very small effects analogous to electromagnetic phenomena are predicted. In a following paper, "Photons in the Gravitational Field", the gravitational red shift and the gravitational deflection of a light ray are deduced correctly.

scholarly journals Lunar and terrestrial planet formation in the Grand Tack scenario

2014 ◽  
Vol 372 (2024) ◽  
pp. 20130174 ◽  
Author(s):  
S. A. Jacobson ◽  
A. Morbidelli
Keyword(s):  
Total Mass ◽  
Planet Formation ◽  
Terrestrial Planet ◽  
Terrestrial Planets ◽  
The Moon ◽  
Giant Impact ◽  
Modal Mass ◽  
The Individual ◽  
Impact Phase ◽  
Geochemical Constraints

We present conclusions from a large number of N -body simulations of the giant impact phase of terrestrial planet formation. We focus on new results obtained from the recently proposed Grand Tack model, which couples the gas-driven migration of giant planets to the accretion of the terrestrial planets. The giant impact phase follows the oligarchic growth phase, which builds a bi-modal mass distribution within the disc of embryos and planetesimals. By varying the ratio of the total mass in the embryo population to the total mass in the planetesimal population and the mass of the individual embryos, we explore how different disc conditions control the final planets. The total mass ratio of embryos to planetesimals controls the timing of the last giant (Moon-forming) impact and its violence. The initial embryo mass sets the size of the lunar impactor and the growth rate of Mars. After comparing our simulated outcomes with the actual orbits of the terrestrial planets (angular momentum deficit, mass concentration) and taking into account independent geochemical constraints on the mass accreted by the Earth after the Moon-forming event and on the time scale for the growth of Mars, we conclude that the protoplanetary disc at the beginning of the giant impact phase must have had most of its mass in Mars-sized embryos and only a small fraction of the total disc mass in the planetesimal population. From this, we infer that the Moon-forming event occurred between approximately 60 and approximately 130 Myr after the formation of the first solids and was caused most likely by an object with a mass similar to that of Mars.

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