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We investigate the possibility that a strong core dynamo of the Moon has magnetized the lunar crust. The magnetic data from two missions, Lunar Prospector and Kaguya, are used and the magnetic fields of two different features are ...
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We investigate the possibility that a strong core dynamo of the Moon has magnetized the lunar crust. The magnetic data from two missions, Lunar Prospector and Kaguya, are used and the magnetic fields of two different features are examined: The isolated small magnetic source bodies with aμmost no topographic signatures, and the impact craters with diameters larger than 100 km. Five data sets are examined separately for each of the isolated magnetic anomalies: the r, h, and φ components of the Lunar Prospector data, the r component of a 150-degree spherical harmonic model of the lunar magnetic field, and the r component of the Kaguya data. The r component of the Lunar Prospector data is also used to derive the magnetic field over the impact craters. We conclude that most of the ancient lunar far side crust is heterogeneously magnetized with coherency wavelength about a few hundred km. The paleomagnetic north poles determined from modeling the magnetic field of both features show some clustering whereas the source bodies are widely distributed, suggesting that the magnetizing field may have been a core dynamo field. Paleointensity data suggest that the core field intensity was at least 1 mT at the core mantle boundary. There is also evidence for core field reversals, because further clustering occurs when the south poles of some features are considered.
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We present an improved lunar digital elevation model (DEM) covering latitudes within 60, at a horizontal resolution of 512 pixels per degree (similar to 60 m at the equator) and a typical vertical accuracy similar to 3 to 4 m. Thi...
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We present an improved lunar digital elevation model (DEM) covering latitudes within 60, at a horizontal resolution of 512 pixels per degree (similar to 60 m at the equator) and a typical vertical accuracy similar to 3 to 4 m. This DEM is constructed from similar to 4.5 x 10(9) geodetically-accurate topographic heights from the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter, to which we co-registered 43,200 stereo-derived DEMs (each 1 degrees x 1 degrees) from the SELENE Terrain Camera (TC) (similar to 10(10) pixels total). After co-registration, approximately 90% of the TC DEMs show root-mean-square vertical residuals with the LOLA data of <5 m compared to similar to 50% prior to co-registration. We use the co-registered TC data to estimate and correct orbital and pointing geolocation errors from the LOLA altimetric profiles (typically amounting to <10 m horizontally and <1 m vertically). By combining both co-registered datasets, we obtain a near-global DEM with high geodetic accuracy, and without the need for surface interpolation. We evaluate the resulting LOLA + TC merged DEM (designated as "SLDEM2015") with particular attention to quantifying seams and crossover errors. (C) 2015 The Authors. Published by Elsevier Inc.
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We utilize a theoretical analysis of the generation, ascent, intrusion and eruption of basaltic magma on the Moon to develop new insights into magma source depths, supply processes, transport and emplacement mechanisms via dike in...
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We utilize a theoretical analysis of the generation, ascent, intrusion and eruption of basaltic magma on the Moon to develop new insights into magma source depths, supply processes, transport and emplacement mechanisms via dike intrusions, and effusive and explosive eruptions. We make predictions about the intrusion and eruption processes and compare these with the range of observed styles of mare volcanism, and related features and deposits. Density contrasts between the bulk mantle and regions with a greater abundance of heat sources will cause larger heated regions to rise as buoyant melt-rich diapirs that generate partial melts that can undergo collection into magma source regions; diapirs rise to the base of the anorthositic crustal density trap (when the crust is thicker than the elastic lithosphere) or, later in history, to the base of the lithospheric rheological trap (when the thickening lithosphere exceeds the thickness of the crust). Residual diapiric buoyancy, and continued production and arrival of diapiric material, enhances melt volume and overpressurizes the source regions, producing sufficient stress to cause brittle deformation of the elastic part of the overlying lithosphere; a magma-filled crack initiates and propagates toward the surface as a convex upward, blade-shaped dike. The volume of magma released in a single event is likely to lie in the range 10(2) km(3) to 10(3) km(3), corresponding to dikes with widths of 40-100 m and both vertical and horizontal extents of 60-100 km, favoring eruption on the lunar nearside. Shallower magma sources produce dikes that are continuous from the source region to the surface, but deeper sources will propagate dikes that detach from the source region and ascend as discrete penny-shaped structures. As the Moon cools with time, the lithosphere thickens, source regions become less abundant, and rheological traps become increasingly deep; the state of stress in the lithosphere becomes increasingly contractional, inhibiting dike emplacement and surface eruptions.
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摘要 :Highlights?Gravity mapping observations from NASA’s GRAIL mission are employed to detect, characterize and validate the presence of large impact craters buried beneath the lunar maria.?Gravity gradiometry detection str...
展开Highlights?Gravity mapping observations from NASA’s GRAIL mission are employed to detect, characterize and validate the presence of large impact craters buried beneath the lunar maria.?Gravity gradiometry detection strategy is applied to both free-air and Bouguer gravity field to identify gravitational signatures that are similar to those observed over buried craters.?The presence of buried craters is further supported by individual analysis of regional free-air gravity anomalies, Bouguer gravity anomaly maps, and forward modeling.?Other large, still unrecognized, craters undoubtedly underlie other portions of the Moon’s vast mare lavas.收起
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GRAIL observations have been used to derive an updated catalog of lunar impact basins with diameters >= 450 km. In this study, we assess the age and relaxation state of these basins and find that the 13-15 stratigraphically younge...
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GRAIL observations have been used to derive an updated catalog of lunar impact basins with diameters >= 450 km. In this study, we assess the age and relaxation state of these basins and find that the 13-15 stratigraphically younger basins are significantly less relaxed than the 8-16 identifiable older basins. The change in relaxation state is most likely a signature of the cooling of the base of the lunar crust below 1300-1400 K, which we infer happened between 4.21-4.45 Ga based on geochronological measurements. We compare the predicted number of basins before and after this reference point with several different modeled lunar cratering chronologies. While these models are sensitive to the ratio of 1km:450 km craters, we conclude that a model with a broad period of late heavy bombardment (a "sawtooth") is more likely to fit both the number of relaxed and unrelaxed basins, and the mass of material delivered as a late veneer.
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We have developed a new method for regional mapping of the lunar magnetic anomalies as the vector field at the surface using the satellite observation, that is the surface vector mapping (SVM). The SVM is based on the inverse boun...
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We have developed a new method for regional mapping of the lunar magnetic anomalies as the vector field at the surface using the satellite observation, that is the surface vector mapping (SVM). The SVM is based on the inverse boundary value problem with a spherical boundary surface. There are two main procedures for reducing effects of bias and noise on mapping: (1) preprocessing the data to provide first derivatives along the pass, and (2) the Bayesian statistical procedure in the inversion using Akaike's Bayesian Information Criterion. The SVM was applied to two regions: the northwest region of the South Pole-Aitken basin as a strong magnetic anomaly region, and the southeast region of the lunar near side as a weak magnetic anomaly region. Since the results from the different datasets of the Kaguya and Lunar Prospector observations show good consistency, characteristic features of the lunar magnetic anomalies at the surface are considered to be well estimated except for components of wavelength shorter than about 1o. From the results by the SVM, both of the regions show elongation patterns of the lunar magnetic anomalies, suggesting lineated structures of the magnetic anomaly sources.
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From Earth, we see the Moon as a thumb-sized, ?2°-diameter disk in the sky. Even with a small telescope, myriad craters and dark plains are visible, but it can be hard to grasp the true sizes of these features. Now, with humans a...
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From Earth, we see the Moon as a thumb-sized, ?2°-diameter disk in the sky. Even with a small telescope, myriad craters and dark plains are visible, but it can be hard to grasp the true sizes of these features. Now, with humans about to return to the Moon with the ultimate goal of a permanent presence, you may want to relate sizes of the lunar features you see in your scope with terrestrial landforms.
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The Gruithuisen domes, situated on the western portion of the Imbrium basin rim, form three tall mountains (NW, Gamma, Delta) totaling similar to 780 km(3) in volume. The shapes of the domes are significantly different from that o...
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The Gruithuisen domes, situated on the western portion of the Imbrium basin rim, form three tall mountains (NW, Gamma, Delta) totaling similar to 780 km(3) in volume. The shapes of the domes are significantly different from that of mare-type domes elsewhere on the Moon. We use data from the Lunar Reconnaissance Orbiter (LRO) and Kaguya missions (LRO Lunar Orbiter Laser Altimeter, Lunar Reconnaissance Orbiter Camera, Diviner, and the Kaguya imager) to characterize the domes and assess models for their origin. The configuration of the domes (steep slopes, up to similar to 18-20 degrees) and their specific remote sensing characteristics (strong downturn in the UV, and results from the M3 and Diviner instruments) suggest that the domes formed by eruptions of highly viscous lava. The estimated surface volumes of the domes vary from similar to 20 km(3) (NW dome) to similar to 290 km(3) (Gamma dome) to similar to 470 km(3) (Delta dome). The domes occur on the portion of the Imbrium basin rim that is overlain by ejecta from the post-Imbrium Iridum crater. In some areas, relatively high albedo smooth volcanic plains are seen within the Iridum ejecta near the Gruithuisen domes, and low albedo mare deposits surround and embay the domes and Iridum crater. Dating of different units and features by crater counts indicates that impact melts from the Iridum basin are similar to 3.9 Ga old, the domes Gamma and Delta are similar to 3.8 Ga, and the ages of the plains near the domes vary from similar to 2.3 to similar to 3.6 Ga. A fresh impact crater exposes the internal structure of the Gamma dome. The most prominent features on the wall of the crater are rough, blocky layers that are typical of volcanic plains in the highlands and maria around the domes. The layers are interleaved with fine-grained materials of higher and lower albedo and the visible orientation of the layers changes over short (a few hundred meters) distances. These characteristics of the internal structure of the dome are consistent with eruptions of high viscosity lava (rough layers) that alternated with possible explosive activity (fine-grained materials). The spatial association of the Gruithuisen domes with the highland lava plains resembles the situation in which bimodal volcanism occur on Earth. The terrestrial association can be due to either fractional crystallization in basaltic magma reservoirs or remelting of high-silica crustal materials. In the first case, the evolved melts appear in later stages of volcanic activity and in the second case these melts are formed near the beginning of evolution of the magmatic systems. The age estimates of the Gruithuisen domes and the surrounding volcanic plains are more consistent with the crustal remelting scenario. However, remelting of primary anorthositic crust cannot readily produce the silica-rich melts and requires the presence of pre-existing granite-like materials. Formation of the domes by fractional crystallization avoids this difficulty but requires explanation of the older age of the domes relative to the volcanic plains in the surroundings. A third option is that the domes are unrelated genetically to the mare deposits. (C) 2015 Elsevier Inc. All rights reserved.
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The lunar photometric function, which describes the dependency of the observed radiance on the observation geometry, is used for photometric correction of lunar visible/near-infrared data. A precise photometric correction paramete...
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The lunar photometric function, which describes the dependency of the observed radiance on the observation geometry, is used for photometric correction of lunar visible/near-infrared data. A precise photometric correction parameter set is crucial for many applications including mineral identification and reflectance map mosaics. We present, for the first time, spectrally continuous photometric correction parameters for both sides of the Moon for wavelengths in the range 0.5-1.6μm and solar phase angles between 5° and 85°, derived from Kaguya (SELENE) Spectral Profiler (SP) data. Since the measured radiance also depends on the surface albedo, we developed a statistical method for selecting areas with relatively uniform albedos from a nearly 7000-orbit SP data set. Using the selected data set, we obtained empirical photometric correction parameter sets for three albedo groups (high, medium, and low). We did this because the photometric function depends on the albedo, especially at phase angles below about 20° for which the shadow hiding opposition effect is appreciable. We determined the parameters in 160 bands and discovered a small variation in the opposition effect due to the albedo variation of mafic mineral absorption. The consistency of the photometric correction was checked by comparing observations made at different times of the same area on the lunar surface. Variations in the spectra obtained were lower than 2%, except for the large phase angle data in mare. Lastly, we developed a correction method for low solar elevation data, which is required for high latitude regions. By investigating low solar elevation data, we introduced an additional correction method. We used the new photometric correction to generate a 1° mesh global lunar reflectance map cube in a wavelength range of 0.5-1.6μm. Surprisingly, these maps reveal that high latitude (?75°) regions in both the north and south have much lower spectral continuum slopes (color ratio r_(1547.7nm)/r_(752.8nm)?1.8) than the low and medium latitude regions, which implies lower degrees of space weathering.
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