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Alexander Konopliv - One of the best experts on this subject based on the ideXlab platform.
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Lunar interior properties from the GRAIL mission
Journal of Geophysical Research. Planets, 2014Co-Authors: James Williams, Sander Goossens, Alexander Konopliv, Dale Boggs, Ryan Park, Dah-ning Yuan, Frank Lemoine, Erwan Mazarico, Francis Nimmo, Renee WeberAbstract:The Gravity Recovery and Interior Laboratory (GRAIL) mission has sampled lunar gravity with unprecedented accuracy and resolution. The lunar GM, the product of the gravitational constant G and the mass M, is very well determined. However, uncertainties in the mass and mean density, 3345.56 ± 0.40 kg/m 3 , are limited by the accuracy of G. Values of the spherical harmonic degree-2 gravity coefficients J 2 and C 22 , as well as the Love number k 2 describing lunar degree-2 elastic response to tidal forces, come from two independent analyses of the 3 month GRAIL Primary Mission data at the Jet Propulsion Laboratory and the Goddard Space Flight Center. The two k 2 determinations, with uncertainties of~1%, differ by 1%; the average value is 0.02416 ± 0.00022 at a 1 month period with reference radius R = 1738 km. Lunar laser ranging (LLR) data analysis determines (C À A)/B and (B À A)/C, where A < B < C are the principal moments of inertia; the flattening of the fluid outer core; the dissipation at its solid boundaries; and the monthly tidal dissipation Q = 37.5 ± 4. The moment of inertia computation combines the GRAIL-determined J 2 and C 22 with LLR-derived (C À A)/B and (B À A)/C. The normalized mean moment of inertia of the solid Moon is I s /MR 2 = 0.392728 ± 0.000012. Matching the density, moment, and Love number, calculated models have a fluid outer core with radius of 200-380 km, a solid inner core with radius of 0-280 km and mass fraction of 0-1%, and a deep mantle zone of low seismic shear velocity. The mass fraction of the combined inner and outer core is ≤1.5%.
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the jpl lunar gravity field to spherical harmonic degree 660 from the GRAIL primary mission
Journal of Geophysical Research, 2013Co-Authors: Alexander Konopliv, James G. Williams, Sami W. Asmar, Dah-ning Yuan, Ryan S Park, M M Watkins, Eugene Fahnestock, Gerhard Kruizinga, Meegyeong Paik, Dmitry StrekalovAbstract:[1] The lunar gravity field and topography provide a way to probe the interior structure of the Moon. Prior to the Gravity Recovery and Interior Laboratory (GRAIL) mission, knowledge of the lunar gravity was limited mostly to the nearside of the Moon, since the farside was not directly observable from missions such as Lunar Prospector. The farside gravity was directly observed for the first time with the SELENE mission, but was limited to spherical harmonic degree n ≤ 70. The GRAIL Primary Mission, for which results are presented here, dramatically improves the gravity spectrum by up to ~4 orders of magnitude for the entire Moon and for more than 5 orders-of-magnitude over some spectral ranges by using interspacecraft measurements with near 0.03 μm/s accuracy. The resulting GL0660B (n = 660) solution has 98% global coherence with topography to n = 330, and has variable regional surface resolution between n = 371 (14.6 km) and n = 583 (9.3 km) because the gravity data were collected at different spacecraft altitudes. The GRAIL data also improve low-degree harmonics, and the uncertainty in the lunar Love number has been reduced by ~5× to k2 = 0.02405 ± 0.00018. The reprocessing of the Lunar Prospector data indicates ~3× improved orbit uncertainty for the lower altitudes to ~10 m, whereas the GRAIL orbits are determined to an accuracy of 20 cm.
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Preliminary Results on Lunar Interior Properties from the GRAIL Mission
2013Co-Authors: James G. Williams, Roger J. Phillips, David E. Smith, H. Jay Melosh, Gregory A. Neumann, Sean C. Solomon, Alexander Konopliv, Sami Asmar, H. Jay Lemoine, Michael WatkinsAbstract:The Gravity Recovery and Interior Laboratory (GRAIL) mission has provided lunar gravity with unprecedented accuracy and resolution. GRAIL has produced a high-resolution map of the lunar gravity field while also determining tidal response. We present the latest gravity field solution and its preliminary implications for the Moon's interior structure, exploring properties such as the mean density, moment of inertia of the solid Moon, and tidal potential Love number k2. Lunar structure includes a thin crust, a deep mantle, a fluid core, and a suspected solid inner core. An accurate Love number mainly improves knowledge of the fluid core and deep mantle. In the future GRAIL will search for evidence of tidal dissipation and a solid inner core.
Peter W Voorhees - One of the best experts on this subject based on the ideXlab platform.
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phase field crystal simulation of grain boundary motion grain rotation and dislocation reactions in a bcc bicrystal
Acta Materialia, 2017Co-Authors: Akinori Yamanaka, Kevin Mcreynolds, Peter W VoorheesAbstract:Abstract We investigate grain boundary motion and grain rotation in a body-centered cubic bicrystal composed of a spherical grain embedded in a single crystal matrix by three-dimensional phase-field crystal simulations. Structure and time evolution of dislocation networks formed on the grain boundary during the capillarity-driven grain shrinkage are examined. The results for initially spherical grains rotated about the [110] or [111] axes of the matrix grain reveal the formation of hexagonal dislocation networks (HDNs) on the grain boundary. We demonstrate that the anisotropic distribution of the HDNs is responsible for asymmetric shrinkage of the embedded grain. Through a detailed analysis of the HDNs, we clarify the mechanisms of dislocation reactions during the grain shrinkage in three dimensions, which include dissociation and recombination of a /2 and a dislocations. The configuration of the HDNs is strongly affected by the rotation axis of the embedded grain. For large misorientations, the high density of the HDNs accelerates dislocation reactions and leads to very small grain rotations. However, if the misorientation is small and the dislocations are further apart, the lack of dislocation reactions on grain shrinkage results in grain rotation. Even though the rotation axis and the misorientation strongly affect the grain shape and the grain rotation, the kinetics of the grain shrinkage associated with the grain rotation follow the classical theory for grain growth: area of the embedded grain shrinks linearly with time. We also show that the stagnation of the grain rotation slows the shrinkage of the embedded grain.
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phase field crystal simulations of nanocrystalline grain growth in two dimensions
Acta Materialia, 2012Co-Authors: Peter W VoorheesAbstract:Abstract We study two-dimensional grain growth at the nanoscale using the phase field crystal (PFC) model. Our results show that for circular grains with large misorientations the grain area decreases linearly with time, in good agreement with classical grain growth theory. For circular grains with small initial misorientations, grain rotation occurs as a result of the coupled motion between the normal motion of the grain boundary and the tangential motion of the adjacent grains. Despite this rotation and its effect on the grain boundary energy, the grain area decreases linearly with time. In addition, for intermediate initial grain misorientations, we find a repeating faceting–defaceting transition during grain shrinkage and a different relationship between the grain area and time, which suggests a different grain growth mechanism than that for small and large misorientations. For a circular grain embedded between a bicrystal with a symmetric tilt boundary, we find that the evolution of the embedded grain closely depends on dislocation reactions at triple junctions.
Dah-ning Yuan - One of the best experts on this subject based on the ideXlab platform.
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Lunar interior properties from the GRAIL mission
Journal of Geophysical Research. Planets, 2014Co-Authors: James Williams, Sander Goossens, Alexander Konopliv, Dale Boggs, Ryan Park, Dah-ning Yuan, Frank Lemoine, Erwan Mazarico, Francis Nimmo, Renee WeberAbstract:The Gravity Recovery and Interior Laboratory (GRAIL) mission has sampled lunar gravity with unprecedented accuracy and resolution. The lunar GM, the product of the gravitational constant G and the mass M, is very well determined. However, uncertainties in the mass and mean density, 3345.56 ± 0.40 kg/m 3 , are limited by the accuracy of G. Values of the spherical harmonic degree-2 gravity coefficients J 2 and C 22 , as well as the Love number k 2 describing lunar degree-2 elastic response to tidal forces, come from two independent analyses of the 3 month GRAIL Primary Mission data at the Jet Propulsion Laboratory and the Goddard Space Flight Center. The two k 2 determinations, with uncertainties of~1%, differ by 1%; the average value is 0.02416 ± 0.00022 at a 1 month period with reference radius R = 1738 km. Lunar laser ranging (LLR) data analysis determines (C À A)/B and (B À A)/C, where A < B < C are the principal moments of inertia; the flattening of the fluid outer core; the dissipation at its solid boundaries; and the monthly tidal dissipation Q = 37.5 ± 4. The moment of inertia computation combines the GRAIL-determined J 2 and C 22 with LLR-derived (C À A)/B and (B À A)/C. The normalized mean moment of inertia of the solid Moon is I s /MR 2 = 0.392728 ± 0.000012. Matching the density, moment, and Love number, calculated models have a fluid outer core with radius of 200-380 km, a solid inner core with radius of 0-280 km and mass fraction of 0-1%, and a deep mantle zone of low seismic shear velocity. The mass fraction of the combined inner and outer core is ≤1.5%.
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the jpl lunar gravity field to spherical harmonic degree 660 from the GRAIL primary mission
Journal of Geophysical Research, 2013Co-Authors: Alexander Konopliv, James G. Williams, Sami W. Asmar, Dah-ning Yuan, Ryan S Park, M M Watkins, Eugene Fahnestock, Gerhard Kruizinga, Meegyeong Paik, Dmitry StrekalovAbstract:[1] The lunar gravity field and topography provide a way to probe the interior structure of the Moon. Prior to the Gravity Recovery and Interior Laboratory (GRAIL) mission, knowledge of the lunar gravity was limited mostly to the nearside of the Moon, since the farside was not directly observable from missions such as Lunar Prospector. The farside gravity was directly observed for the first time with the SELENE mission, but was limited to spherical harmonic degree n ≤ 70. The GRAIL Primary Mission, for which results are presented here, dramatically improves the gravity spectrum by up to ~4 orders of magnitude for the entire Moon and for more than 5 orders-of-magnitude over some spectral ranges by using interspacecraft measurements with near 0.03 μm/s accuracy. The resulting GL0660B (n = 660) solution has 98% global coherence with topography to n = 330, and has variable regional surface resolution between n = 371 (14.6 km) and n = 583 (9.3 km) because the gravity data were collected at different spacecraft altitudes. The GRAIL data also improve low-degree harmonics, and the uncertainty in the lunar Love number has been reduced by ~5× to k2 = 0.02405 ± 0.00018. The reprocessing of the Lunar Prospector data indicates ~3× improved orbit uncertainty for the lower altitudes to ~10 m, whereas the GRAIL orbits are determined to an accuracy of 20 cm.
Dmitry Strekalov - One of the best experts on this subject based on the ideXlab platform.
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the jpl lunar gravity field to spherical harmonic degree 660 from the GRAIL primary mission
Journal of Geophysical Research, 2013Co-Authors: Alexander Konopliv, James G. Williams, Sami W. Asmar, Dah-ning Yuan, Ryan S Park, M M Watkins, Eugene Fahnestock, Gerhard Kruizinga, Meegyeong Paik, Dmitry StrekalovAbstract:[1] The lunar gravity field and topography provide a way to probe the interior structure of the Moon. Prior to the Gravity Recovery and Interior Laboratory (GRAIL) mission, knowledge of the lunar gravity was limited mostly to the nearside of the Moon, since the farside was not directly observable from missions such as Lunar Prospector. The farside gravity was directly observed for the first time with the SELENE mission, but was limited to spherical harmonic degree n ≤ 70. The GRAIL Primary Mission, for which results are presented here, dramatically improves the gravity spectrum by up to ~4 orders of magnitude for the entire Moon and for more than 5 orders-of-magnitude over some spectral ranges by using interspacecraft measurements with near 0.03 μm/s accuracy. The resulting GL0660B (n = 660) solution has 98% global coherence with topography to n = 330, and has variable regional surface resolution between n = 371 (14.6 km) and n = 583 (9.3 km) because the gravity data were collected at different spacecraft altitudes. The GRAIL data also improve low-degree harmonics, and the uncertainty in the lunar Love number has been reduced by ~5× to k2 = 0.02405 ± 0.00018. The reprocessing of the Lunar Prospector data indicates ~3× improved orbit uncertainty for the lower altitudes to ~10 m, whereas the GRAIL orbits are determined to an accuracy of 20 cm.
Sami W. Asmar - One of the best experts on this subject based on the ideXlab platform.
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the jpl lunar gravity field to spherical harmonic degree 660 from the GRAIL primary mission
Journal of Geophysical Research, 2013Co-Authors: Alexander Konopliv, James G. Williams, Sami W. Asmar, Dah-ning Yuan, Ryan S Park, M M Watkins, Eugene Fahnestock, Gerhard Kruizinga, Meegyeong Paik, Dmitry StrekalovAbstract:[1] The lunar gravity field and topography provide a way to probe the interior structure of the Moon. Prior to the Gravity Recovery and Interior Laboratory (GRAIL) mission, knowledge of the lunar gravity was limited mostly to the nearside of the Moon, since the farside was not directly observable from missions such as Lunar Prospector. The farside gravity was directly observed for the first time with the SELENE mission, but was limited to spherical harmonic degree n ≤ 70. The GRAIL Primary Mission, for which results are presented here, dramatically improves the gravity spectrum by up to ~4 orders of magnitude for the entire Moon and for more than 5 orders-of-magnitude over some spectral ranges by using interspacecraft measurements with near 0.03 μm/s accuracy. The resulting GL0660B (n = 660) solution has 98% global coherence with topography to n = 330, and has variable regional surface resolution between n = 371 (14.6 km) and n = 583 (9.3 km) because the gravity data were collected at different spacecraft altitudes. The GRAIL data also improve low-degree harmonics, and the uncertainty in the lunar Love number has been reduced by ~5× to k2 = 0.02405 ± 0.00018. The reprocessing of the Lunar Prospector data indicates ~3× improved orbit uncertainty for the lower altitudes to ~10 m, whereas the GRAIL orbits are determined to an accuracy of 20 cm.
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Properties of the Lunar Interior: Preliminary Results from the GRAIL Mission
2013Co-Authors: James G. Williams, Roger J. Phillips, Sami W. Asmar, Alexander S. Konopliv, Frank G. Lemoine, H. Jay Melosh, Gregory A. Neumann, Sean C. Solomon, David Eugene Smith, Michael M. WatkinsAbstract:The Gravity Recovery and Interior Laboratory (GRAIL) mission [1] has provided lunar gravity with unprecedented accuracy and resolution. GRAIL has produced a high-resolution map of the lunar gravity field [2,3] while also determining tidal response. We present the latest gravity field solution and its preliminary implications for the Moon's interior structure, exploring properties such as the mean density, moment of inertia of the solid Moon, and tidal potential Love number k(sub 2). Lunar structure includes a thin crust, a thick mantle layer, a fluid outer core, and a suspected solid inner core. An accurate Love number mainly improves knowledge of the fluid core and deep mantle. In the future, we will search for evidence of tidal dissipation and a solid inner core using GRAIL data.
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Gravity field of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL) mission.
Science (New York N.Y.), 2012Co-Authors: Maria T. Zuber, Roger J. Phillips, David E. Smith, Michael M. Watkins, Sami W. Asmar, Alexander S. Konopliv, Frank G. Lemoine, H. Jay Melosh, Gregory A. Neumann, Sean C. SolomonAbstract:Spacecraft-to-spacecraft tracking observations from the Gravity Recovery and Interior Laboratory (GRAIL) have been used to construct a gravitational field of the Moon to spherical harmonic degree and order 420. The GRAIL field reveals features not previously resolved, including tectonic structures, volcanic landforms, basin rings, crater central peaks, and numerous simple craters. From degrees 80 through 300, over 98% of the gravitational signature is associated with topography, a result that reflects the preservation of crater relief in highly fractured crust. The remaining 2% represents fine details of subsurface structure not previously resolved. GRAIL elucidates the role of impact bombardment in homogenizing the distribution of shallow density anomalies on terrestrial planetary bodies.
