388 research outputs found
Geophysical Exploration of Vesta
Dawnâs year-long stay at Vesta allows
comprehensive mapping of the shape, topography,
geology, mineralogy, elemental abundances, and
gravity field using itâs three instruments and highprecision
spacecraft navigation. In the current Low
Altitude Mapping Orbit (LAMO), tracking data is being
acquired to develop a gravity field expected to be
accurate to degree and order ~20 [1, 2]. Multi-angle
imaging in the Survey and High Altitude Mapping
Orbit (HAMO) has provided adequate stereo coverage
to develop a shape model accurate to ~10 m at 100 m
horizontal spatial resolution. Accurate mass determination
combined with the shape yields a more precise
value of bulk density, albeit with some uncertainty
resulting from the unmeasured seasonally-dark north
polar region. The shape and gravity of Vesta can be
used to infer the interior density structure and investigate
the nature of the crust, informing models for Vestaâs
formation and evolution
The reference frames of Mercury after MESSENGER
We report on recent refinements and the current status for the rotational
state models and the reference frame of the planet Mercury. We summarize the
performed measurements of Mercury rotation based on terrestrial radar
observations as well as data from the Mariner 10 and the MESSENGER missions.
Further, we describe the different available definitions of reference systems
for Mercury, which are realized using data obtained by instruments on board
MESSENGER. In particular, we discuss the dynamical frame, the principal-axes
frame, the ellipsoid frame, as well as the cartographic frame. We also describe
the reference frame adopted by the MESSENGER science team for the release of
their cartographic products and we provide expressions for transformations from
this frame to the other reference frames
Visualizing planetary data by using 3D engines
We examined 3D gaming engines for their usefulness
in visualizing large planetary image data sets. These
tools allow us to include recent developments in the
field of computer graphics in our scientific
visualization systems and present data products
interactively and in higher quality than before. We
started to set up the first applications which will take
use of virtual reality (VR) equipment
An Assemblage of Lava Flow Features on Mercury
In contrast to other terrestrial planets, Mercury does not possess a great variety of volcanic features, its history of volcanism instead largely manifest by expansive smooth plains. However, a set of landforms at high northern latitudes on Mercury resembles surface flow features documented on Earth, the Moon, Mars, and Venus. The most striking of such landforms are broad channels that host streamlined islands and that cut through the surrounding intercrater plains. Together with narrower, more sinuous channels, coalesced depressions, evidence for local flooding of intercrater plains by lavas, and a first-order analysis of lava flow rates, the broad channels define an assemblage of flow features formed by the overland flow of, and erosion by, voluminous, high-temperature, low-viscosity lavas. This interpretation is consistent with compositional data suggesting that substantial portions of Mercury's crust are composed of magnesian, iron-poor lithologies. Moreover, the proximity of this partially flooded assemblage to extensive volcanic plains raises the possibility that the formation of these flow features may preface total inundation of an area by lavas emplaced in a flood mode and that they escaped complete burial only due to a waning magmatic supply. Finally, that these broad channels on Mercury are volcanic in nature yet resemble outflow channels on Mars, which are commonly attributed to catastrophic water floods, implies that aqueous activity is not a prerequisite for the formation of such distinctive landforms on any planetary body
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Insights into the subsurface structure of the Caloris basin, Mercury, from assessments of mechanical layering and changes in long-wavelength topography
The volcanic plains that fill the Caloris basin, the largest recognized impact basin on Mercury, are deformed by many graben and wrinkle ridges, among which the multitude of radial graben of Pantheon Fossae allow us to resolve variations in the depth extent of associated faulting. Displacement profiles and displacement-to-length scaling both indicate that faults near the basin center are confined to a ~ 4-km-thick mechanical layer, whereas faults far from the center penetrate more deeply. The fault scaling also indicates that the graben formed in mechanically strong material, which we identify with dry basalt-like plains. These plains were also affected by changes in long-wavelength topography, including undulations with wavelengths of up to 1300 km and amplitudes of 2.5 to 3 km. Geographic correlation of the depth extent of faulting with topographic variations allows a first-order interpretation of the subsurface structure and mechanical stratigraphy in the basin. Further, crosscutting and superposition relationships among plains, faults, craters, and topography indicate that development of long-wavelength topographic variations followed plains emplacement, faulting, and much of the cratering within the Caloris basin. As several examples of these topographic undulations are also found outside the basin, our results on the scale, structural style, and relative timing of the topographic changes have regional applicability and may be the surface expression of global-scale interior processes on Mercury
Recommended from our members
Insights into the subsurface structure of the Caloris basin, Mercury, from assessments of mechanical layering and changes in long-wavelength topography
The volcanic plains that fill the Caloris basin, the largest recognized impact basin on Mercury, are deformed by many graben and wrinkle ridges, among which the multitude of radial graben of Pantheon Fossae allow us to resolve variations in the depth extent of associated faulting. Displacement profiles and displacement-to-length scaling both indicate that faults near the basin center are confined to a ~ 4-km-thick mechanical layer, whereas faults far from the center penetrate more deeply. The fault scaling also indicates that the graben formed in mechanically strong material, which we identify with dry basalt-like plains. These plains were also affected by changes in long-wavelength topography, including undulations with wavelengths of up to 1300 km and amplitudes of 2.5 to 3 km. Geographic correlation of the depth extent of faulting with topographic variations allows a first-order interpretation of the subsurface structure and mechanical stratigraphy in the basin. Further, crosscutting and superposition relationships among plains, faults, craters, and topography indicate that development of long-wavelength topographic variations followed plains emplacement, faulting, and much of the cratering within the Caloris basin. As several examples of these topographic undulations are also found outside the basin, our results on the scale, structural style, and relative timing of the topographic changes have regional applicability and may be the surface expression of global-scale interior processes on Mercury
Ceres' spectral link to carbonaceous chondrites - Analysis of the dark background materials
Ceresâ surface has commonly been linked with carbonaceous chondrites (CCs) by groundâbased telescopic observations, because of its low albedo, flat to redâsloped spectra in the visible and nearâinfrared (VIS/NIR) wavelength region, and the absence of distinct absorption bands, though no currently known meteorites provide complete spectral matches to Ceres. Spatially resolved data of the Dawn Framing Camera (FC) reveal a generally dark surface covered with bright spots exhibiting reflectance values several times higher than Ceresâ background. In this work, we investigated FC data from High Altitude Mapping Orbit (HAMO) and Ceres eXtended Juling (CXJ) orbit (~140 m/pixel) for global spectral variations. We found that the cerean surface mainly differs by spectral slope over the whole FC wavelength region (0.4â1.0 ÎŒm). Areas exhibiting slopes <â10% ÎŒmâ1 constitute only ~3% of the cerean surface and mainly occur in the bright material in and around young craters, whereas slopes â„â10% ÎŒmâ1 occur on more than 90% of the cerean surface; the latter being denoted as Ceresâ background material in this work. FC and Visible and Infrared Spectrometer (VIR) spectra of this background material were compared to the suite of CCs spectrally investigated so far regarding their VIS/NIR region and 2.7 ÎŒm absorption, as well as their reflectance at 0.653 ÎŒm. This resulted in a good match to heated CI Ivuna (heated to 200â300 °C) and a better match for CM1 meteorites, especially Moapa Valley. This possibly indicates that the alteration of CM2 to CM1 took place on Ceres
Thermal fracturing on comets: Applications to 67P/Churyumov-Gerasimenko
We simulate the stresses induced by temperature changes in a putative hard layer near the surface of comet 67P/Churyumov-Gerasimenko with a thermo-viscoelastic model. Such a layer could be formed by the recondensation or sintering of water ice (and dust grains), as suggested by laboratory experiments and computer simulations, and would explain the high compressive strength encountered by experiments on board the Philae lander. Changes in temperature from seasonal insolation variation penetrate into the cometâs surface to depths controlled by the thermal inertia, causing the material to expand and contract. Modelling this with a Maxwellian viscoelastic response on a spherical nucleus, we show that a hard, icy layer with similar properties to Martian permafrost will experience high stresses: up to tens of MPa, which exceed its material strength (a few MPa), down to depths of centimetres to a metre. The stress distribution with latitude is confirmed qualitatively when taking into account the cometâs complex shape but neglecting thermal inertia. Stress is found to be comparable to the material strength everywhere for sufficient thermal inertia (âł 50 J mâ2 Kâ1 sâ1â2) and ice content (âł 45% at the equator). In this case, stresses penetrate to a typical depth of ~0.25 m, consistent with the detection of metre-scale thermal contraction crack polygons all over the comet. Thermal fracturing may be an important erosion process on cometary surfaces which breaks down material and weakens cliffs
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