Dark material on Vesta from the infall of carbonaceous volatile-rich material

McCord, T. B.; Li, J.-Y; Combe, J.-P.; McSween, H. Y.; Jaumann, R.; Reddy, V.; Tosi, F.; Williams, D. A.; Blewett, D. T.; Turrini, D.; Palomba, E.; Pieters, C. M.; Sanctis, M. C. De; Ammannito, E.; Capria, M. T.; Corre, Lucille Le; Longobardo, A.; Nathues, A.; Mittlefehldt, D. W.; Schröder, Stefan; Hiesinger, H.; Beck, A. W.; Capaccioni, F.; Carsenty, U.; Keller, H. U.; Denevi, Brett W.; Sunshine, J. M.; Raymond, C. A.; Russell, C. T.

doi:10.1038/nature11561

Cited by 152 publications

(175 citation statements)

References 22 publications

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“…Dark material originating from carbonaceous chondrite-rich (CC) objects, especially from the outer parts of the asteroid belt and perhaps from comets, must have impacted Vesta's surface. Further, the spectrum of the dark material end member, as modeled by McCord et al (2012), is similar to that of CC and organic-rich material in the outer Solar System. Exogenic infall is also supported by certain HED (howardites, eucrite, diogenite) meteorites, originating from Vesta (e.g.…”

Section: Introductionmentioning

confidence: 74%

“…Alternatively, it may occur as blocky or layered outcrops in crater walls and as mass-wasting deposits on crater flanks and floors. One apparent conclusion from these observations (Jaumann et al, 2012b;McCord et al, 2012;Reddy et al, 2012) is that the nature of the dark material deposits, whatever their sources, is strongly influenced by impact mixing, gardening and mass-wasting. In addition to the small, well-defined dark material deposits, there are also large regions of low albedo surface material, often with indistinct boundaries, that appear to include dark material.…”

Section: Introductionmentioning

confidence: 95%

“…Material exposed on the surface is classified as dark where its albedo is (1) less than the average albedo and (2) lesser than the surrounding material clearly offset by a traceable unit boundary. Based on this definition, three major dark geological settings have been identified (Jaumann et al, 2012b;McCord et al, 2012): (1) material cropping out at crater walls, scarps and escarpments (dv-ratio 0.7-0.8, da-ratio 0.7-0.9); (2) material on crater rims in ejecta or mass wasting deposits (dv-ratio 0.5-0.8, da-ratio 0.4-0.7), and (3) dark regolith and linear dark features (dv-ratio $0.9, da-ratio $0.8).…”

Section: Data Base and Methodsmentioning

confidence: 99%

“…Geological analyses demonstrate that the dark subsurface layers are close to the surface, relatively thin, and expressed as isolated patches. In principle, two processes are expected to account for such an observation: volcanic deposits or low-velocity impacts implanting dark impactor material into the upper regolith (Jaumann et al, 2012b;McCord et al, 2012).…”

Section: Geological Evidence For the Origin Of Dark Materialsmentioning

confidence: 99%

“…However, regions of very low albedo on Vesta's surface were first discovered by the Dawn mission (Jaumann et al, 2012a;Russell et al, 2012;McCord et al, 2012;Reddy et al, 2012). These dark material deposits are non-randomly distributed over the surface and often associated with geological/morphological features (Jaumann et al, 2012b;McCord et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

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The geological nature of dark material on Vesta and implications for the subsurface structure

Jaumann

Naß

Otto

et al. 2014

Icarus

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a b s t r a c tDeposits of dark material appear on Vesta's surface as features of relatively low-albedo in the visible wavelength range of Dawn's camera and spectrometer. Mixed with the regolith and partially excavated by younger impacts, the material is exposed as individual layered outcrops in crater walls or ejecta patches, having been uncovered and broken up by the impact. Dark fans on crater walls and dark deposits on crater floors are the result of gravity-driven mass wasting triggered by steep slopes and impact seismicity. The fact that dark material is mixed with impact ejecta indicates that it has been processed together with the ejected material. Some small craters display continuous dark ejecta similar to lunar dark-halo impact craters, indicating that the impact excavated the material from beneath a higher-albedo surface. The asymmetric distribution of dark material in impact craters and ejecta suggests non-continuous distribution in the local subsurface. Some positive-relief dark edifices appear to be impact-sculpted hills with dark material distributed over the hill slopes. Dark features inside and outside of craters are in some places arranged as linear outcrops along scarps or as dark streaks perpendicular to the local topography. The spectral characteristics of the dark material resemble that of Vesta's regolith. Dark material is distributed unevenly across Vesta's surface with clusters of all types of dark material exposures. On a local scale, some craters expose or are associated with dark material, while others in the immediate vicinity do not show evidence for dark material. While the variety of surface exposures of dark material and their different geological correlations with surface features, as well as their uneven distribution, indicate a globally inhomogeneous distribution in the subsurface, the dark material seems to be correlated with the rim and ejecta of the older Veneneia south polar basin structure. The origin of the dark material is still being debated, however, the geological analysis suggests that it is exogenic, from carbon-rich low-velocity impactors, rather than endogenic, from freshly exposed mafic material or melt, exposed or created by impacts.

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Section: Introductionmentioning

confidence: 74%

Section: Introductionmentioning

confidence: 95%

Section: Data Base and Methodsmentioning

confidence: 99%

Section: Geological Evidence For the Origin Of Dark Materialsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The geological nature of dark material on Vesta and implications for the subsurface structure

Jaumann

Naß

Otto

et al. 2014

Icarus

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Vesta surface thermal properties map

Capria

Tosi

Sanctis

et al. 2014

Geophysical Research Letters

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The first ever regional thermal properties map of Vesta has been derived from the temperatures retrieved by infrared data by the mission Dawn. The low average value of thermal inertia, 30 ± 10 J m À2 s À0.5 K À1, indicates a surface covered by a fine regolith. A range of thermal inertia values suggesting terrains with different physical properties has been determined. The lower thermal inertia of the regions north of the equator suggests that they are covered by an older, more processed surface. A few specific areas have higher than average thermal inertia values, indicative of a more compact material. The highest thermal inertia value has been determined on the Marcia crater, known for its pitted terrain and the presence of hydroxyl in the ejecta. Our results suggest that this type of terrain can be the result of soil compaction following the degassing of a local subsurface reservoir of volatiles.

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Small fresh impact craters on asteroid 4 Vesta: A compositional and geological fingerprint

et al. 2014

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Small morphologically fresh impact craters (<10 km in diameter) on Vesta's surface with a photometrically distinct ejecta blanket are expected to represent fresh surface material and thus provide the opportunity to study the composition of the unweathered surface. Dawn-Framing Camera and Visual and Infrared Spectrometer (VIR) data reveal impact craters with bright, dark, and mixed, i.e., partly bright and dark, ejecta existing on Vesta's surface, which not only differ in the visible albedo from their surroundings but also in their composition. Differences in the composition are related to the visible albedo and/or the geographic location of the impact craters. Bright ejecta, only seen in the southern Vestan hemisphere, are dominated by howardite/eucrite-like material as expected for Vesta's upper crust. Dark ejecta associated with dark impact craters are dominated by a strongly absorbing, spectrally neutral compound, supporting an origin from carbon-rich impactors. Few impact craters of intermediate albedo in Vesta's southern hemisphere contain material resembling diogenites, which are expected to exist in the deeper parts of Vesta's interior. The geological settings suggest that the diogenite-like material represents a part of a layer of diogenitic material surrounding the Rheasilvia basin or local concentrations of diogenitic material as part of the ejecta excavated during the latter stage of the Rheasilvia impact event. The spectral differences between eucrite-and diogenite-dominated materials also could be verified due to spin-forbidden absorptions in the visible spectral range, which are known from laboratory spectra of pyroxenes, but, which have been identified in the VIR spectra of Vesta for the first time.

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Dark material on Vesta from the infall of carbonaceous volatile-rich material

Cited by 152 publications

References 22 publications

The geological nature of dark material on Vesta and implications for the subsurface structure

The geological nature of dark material on Vesta and implications for the subsurface structure

Vesta surface thermal properties map

Small fresh impact craters on asteroid 4 Vesta: A compositional and geological fingerprint

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