39 research outputs found
Recommended from our members
Identification of buried lunar impact craters from GRAIL data and implications for the nearside maria
Gravity observations from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have revealed more than 100 quasiâcircular mass anomalies, 26â300âkm in diameter, on the lunar nearside. These anomalies are interpreted to be impact craters filled primarily by mare deposits, and their characteristics are consistent with those of impact structures that formed prior to, and during, intervals of flooding of feldspathic terrane by mare basalt lavas. We determine that mare deposits have an average density contrast of 850âșÂłâ°â°ââââ kg mâ»Âł relative to the surrounding crust. The presence of a large population of volcanically buried craters with minimal topographic expression and diameters up to 300âkm requires an average nearside mare thickness of at least 1.5âkm and local lenses of mare basalt as thick as ~7âkm
Revised Thickness of the Lunar Crust from GRAIL Data: Implications for Lunar Bulk Composition
High-resolution gravity data from GRAIL have yielded new estimates of the bulk density and thickness of the lunar crust. The bulk density of the highlands crust is 2550 kg m-3. From a comparison with crustal composition measured remotely, this density implies a mean porosity of 12%. With this bulk density and constraints from the Apollo seismic experiment, the average global crustal thickness is found to lie between 34 and 43 km, a value 10 to 20 km less than several previous estimates. Crustal thickness is a central parameter in estimating bulk lunar composition. Estimates of the concentrations of refractory elements in the Moon from heat flow, remote sensing and sample data, and geophysical data fall into two categories: those with refractory element abundances enriched by 50% or more relative to Earth, and those with abundances the same as Earth. Settling this issue has implications for processes operating during lunar formation. The crustal thickness resulting from analysis of GRAIL data is less than several previous estimates. We show here that a refractory-enriched Moon is not require
Structure and Evolution of the Lunar Procellarum Region as Revealed by GRAIL Gravity Data
The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, thorium, and potassium. The Procellarum region has been interpreted as an ancient impact basin approximately 3200 km in diameter, though supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border the Procellarum region and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dikes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of quasi-rectangular border structures with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the elevated heat flux in the region
Gravity Recovery and Interior Laboratory (GRAIL): Extended Mission and End-Game Status
The Gravity Recovery and Interior Laboratory (GRAIL) [1], NASA s eleventh Discovery mission, successfully executed its Primary Mission (PM) in lunar orbit between March 1, 2012 and May 29, 2012. GRAIL s Extended Mission (XM) initiated on August 30, 2012 and was successfully completed on December 14, 2012. The XM provided an additional three months of gravity mapping at half the altitude (23 km) of the PM (55 km), and is providing higherresolution gravity models that are being used to map the upper crust of the Moon in unprecedented detail
Preliminary Results on Lunar Interior Properties from the GRAIL Mission
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
The fractured Moon: Production and saturation of porosity in the lunar highlands from impact cratering
We have analyzed the Bouguer anomaly (BA) of ~1200 complex craters in the lunar highlands from Gravity Recovery and Interior Laboratory observations. The BA of these craters is generally negative, though positive BA values are observed, particularly for smaller craters. Crater BA values scale inversely with crater diameter, quantifying how larger impacts produce more extensive fracturing and dilatant bulking. The Bouguer anomaly of craters larger than urn:x-wiley:00948276:media:grl53324:grl53324-math-0001âkm in diameter is independent of crater size, indicating that there is a limiting depth to impactâgenerated porosity, presumably from pore collapse associated with either overburden pressure or viscous flow. Impactâgenerated porosity of the bulk lunar crust is likely in a state of equilibrium for craters smaller than ~30âkm in diameter, consistent with an ~8âkm thick lunar megaregolith, whereas the gravity signature of larger craters is still preserved and provides new insight into the cratering record of even the oldest lunar surfaces
Improved functionalization of oleic acid-coated iron oxide nanoparticles for biomedical applications
Superparamagnetic iron oxide nanoparticles
can providemultiple benefits for biomedical applications
in aqueous environments such asmagnetic separation or
magnetic resonance imaging. To increase the colloidal
stability and allow subsequent reactions, the introduction
of hydrophilic functional groups onto the particlesâ
surface is essential. During this process, the original
coating is exchanged by preferably covalently bonded
ligands such as trialkoxysilanes. The duration of the
silane exchange reaction, which commonly takes more
than 24 h, is an important drawback for this approach. In
this paper, we present a novel method, which introduces
ultrasonication as an energy source to dramatically
accelerate this process, resulting in high-quality waterdispersible nanoparticles around 10 nmin size. To prove
the generic character, different functional groups were
introduced on the surface including polyethylene glycol
chains, carboxylic acid, amine, and thiol groups. Their
colloidal stability in various aqueous buffer solutions as
well as human plasma and serum was investigated to
allow implementation in biomedical and sensing
applications.status: publishe
The motivations for the adoption of management innovation by local governments and its performance effects
This article analyses the economic, political and institutional antecedents and performance effects of the adoption of shared Senior Management Teams (SMTs) â a management innovation (MI) that occurs when a team of senior managers oversees two or more public organizations. Findings from statistical analysis of 201 English local governments and interviews with organizational leaders reveal that shared SMTs are adopted to develop organisational capacity in resourceâchallenged, politically riskâaverse governments, and in response to coercive and mimetic institutional pressures. Importantly, sharing SMTs may reduce rather than enhance efficiency and effectiveness due to redundancy costs and the political transaction costs associated with diverting resources away from a highâperforming partner to support their lowerâperforming counterpart
Recommended from our members
Geophysical evidence for an active mantle plume underneath Elysium Planitia on Mars
Although the majority of volcanic and tectonic activity on Mars occurred during the first 1.5 billion years of its geologic history, recent volcanism, tectonism, and active seismicity in Elysium Planitia reveal ongoing activity. However, this recent pulse in volcanism and tectonics is unexpected on a cooling Mars. Here, we present observational evidence and geophysical models demonstrating that Elysium Planitia is underlain by a ~4000-km diameter active mantle plume head. Plume activity provides an explanation for the regional gravity and topography highs, recent volcanism, transition from compressional to extensional tectonics, and ongoing seismicity. The inferred plume head characteristics are comparable to terrestrial plumes that are linked to the formation of large igneous provinces. Our results demonstrate that the interior of Mars is geodynamically active today, and imply that volcanism has been driven by mantle plumes from the formation of the Hesperian volcanic provinces and Tharsis in the past, to Elysium Planitia today.80NSSC17K0059 from the NASA Solar System Workings6 month embargo; published: 05 December 2022This 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]
Recommended from our members
The moon before mare
The crust of the Moon experienced a unique geodynamic evolution, beginning with its crystallization from a magma ocean, continuing through a period of heavy impact bombardment, and followed by extensive basaltic mare volcanism. All these events have left crucial records imprinted in the form of topographic features and gravity anomalies. Here, we invert gravity and topography data using a two-layer thin-shell loading model under the premise of pre-mare isostasy to investigate the global structure of the crust and solve for feldspathic crust and mare thickness, together with mare-induced flexure. The tectonic record and partially buried crater population are used to constrain the bulk of mare volcanism to have been emplaced on a 40 km elastic lithosphere, although mare within large impact basins may have formed on a thinner elastic lithosphere. The mare thickness and associated flexure are removed to calculate a map of the surface and crust of the Moon before mare volcanism. The pre-mare surface in the western Procellarum region is found to be ~2 kilometers lower than the surrounding nearside, and several possible explanations, including a giant impact, pore space annealing, isostatic adjustment, and crustal erosion induced by a mantle plume or thermal anomaly, are discussed. The pre-mare elevation map further sheds light on the ring structure of Imbrium, which is seen to resemble that of Orientale. Imbriumâs outermost ring is observed to be at a larger radial distance to the northeast relative to the south, indicating that some level of lithospheric variability affected ring formation at the time of impact. The western part of Imbriumâs ring within Oceanus Procellarum is not found in the pre-mare topography, implying that it either never formed or that some processes erased its signature from gravity and topography. The feldspathic, pre-mare, crust is found to be ~7 km thinner within large nearside basins than in models not accounting for the high-density mare. The pre-fill floor of these basins was ~6 km deeper than currently observed, and together with their updated crustal structure, these new insights have implications for impact simulations that try to reproduce the crustal structure of nearside mare basins.This work was supported by grant 80NSSC22K1340 from the NASA Lunar Data Analysis Program to JCAH24 month embargo; first published: 30 October 2023This 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]