Impact Excavation on Asteroid 4 Vesta: Hubble Space Telescope Results

Thomas, P. C.; Binzel, Richard P.; Gaffey, M. J.; Storrs, A. D.; Wells, Edward F.; Zellner, B.

doi:10.1126/science.277.5331.1492

Cited by 295 publications

(252 citation statements)

References 29 publications

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“…The asteroid Vesta is of great interest because Earth-based telescopic spectroscopy suggests that it has a basaltic to ultramafic composition (McCord et al, 1970;Binzel et al, 1997;Gaffey, 1997;Thomas et al, 1997;De Sanctis et al, 2012), which matches closely with that of the howardite-eucrite-diogenite (HED) basaltic achondrite meteorites. The presence of basaltic compositions and textures in the HEDs (e.g., McSween et al, 2011;McSween et al, 2013 and references therein) suggest that basaltic lava flows once extruded onto Vesta's surface (e.g., Wilson and Keil, 1996) or alternatively were derived from the crystallized remnants of a global magma ocean (Righter and Drake, 1997;Ruzicka et al, 1997;Warren, 1997), and that Vesta must have differentiated into a crust, mantle, and core (e.g., Keil, 2002;McSween et al, 2011).…”

Section: Introductionmentioning

confidence: 97%

Lobate and flow-like features on asteroid Vesta

Williams

O’Brien

Schenk

et al. 2014

Planetary and Space Science

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a b s t r a c tWe studied high-resolution images of asteroid Vesta's surface ( $ 70 and 20-25 m/pixel) obtained during the High-and Low-Altitude Mapping Orbits (HAMO, LAMO) of NASA's Dawn mission to assess the formation mechanisms responsible for a variety of lobate, flow-like features observed across the surface. We searched for evidence of volcanic flows, based on prior mathematical modeling and the well-known basaltic nature of Vesta's crust, but no unequivocal morphologic evidence of ancient volcanic activity has thus far been identified. Rather, we find that all lobate, flow-like features on Vesta appear to be related either to impact or erosional processes. Morphologically distinct lobate features occur in and around impact craters, and most of these are interpreted as impact ejecta flows, or possibly flows of impact melt. Estimates of melt production from numerical models and scaling laws suggests that large craters like Marcia ( $ 60 km diameter) could have potentially produced impact melt volumes ranging from tens of millions of cubic meters to a few tens of cubic kilometers, which are relatively small volumes compared to similar-sized lunar craters, but which are consistent with putative impact melt features observed in Dawn images. There are also examples of lobate flows that trend downhill both inside and outside of crater rims and basin scarps, which are interpreted as the result of gravity-driven mass movements (slumps and landslides).

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Section: Introductionmentioning

confidence: 97%

Lobate and flow-like features on asteroid Vesta

Williams

O’Brien

Schenk

et al. 2014

Planetary and Space Science

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“…The source of this additional heat may have been from large impacts (Nyquist et al, 1986), heating at depth after burial of surface basalts (Yamaguchi et al, 1996(Yamaguchi et al, , 1997, or the differentiation into layers (Takeda, 1997). A large impact crater of 460 km diameter, 13 km depth with a large central peak, has been identified on Vesta (Thomas et al, 1997) which may have extended beyond the crust into the mantle layer and ejected many Vestoids and HEDs (McSween et al, 2010). The age of this impact crater is controversial, with some evidence suggesting it occurred during the Late Heavy Bombardment period of 3.5-4.0 billion years ago (Scott et al, 2009b), and other evidence supporting an age of only 1 billion years (Asphaug, 1997).…”

Section: Introductionmentioning

confidence: 99%

Zinc isotopes in HEDs: Clues to the formation of 4-Vesta, and the unique composition of Pecora Escarpment 82502

Paniello¹,

Moynier²,

Beck

et al. 2012

Geochimica et Cosmochimica Acta

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The d 66 Zn (permil deviation of the 66 Zn/ 64 Zn ratio from a terrestrial standard) values for a suite of 20 non-Antarctic HED (howardite-eucrite-diogenite) meteorites and one mesosiderite, and for eight Antarctic eucrites and diogenites, were measured in order to determine the role of volatization in the formation of their presumed parent body, the asteroid 4-Vesta. The 20 non-Antarctic HEDs had d 66 Zn values that ranged from À2.0& to +1.67&, with a mean value of À0.01 ± 0.39& (2 se); this range likely represents a small-scale heterogeneity due to brecciation induced by multiple impacts. The non-Antarctic eucrites (d 66 Zn = +0.00 ± 0.58& (2 se), n = 12) were isotopically the same as the diogenites (d 66 Zn = À0.31 ± 0.80& (2 se), n = 4), and the howardites (d 66 Zn = +0.26 ± 0.37& (2 se), n = 4). On average, non-Antarctic eucrite falls were isotopically heavier (+0.50&) than non-Antarctic finds (À1.00&). The Antarctic finds studied were all unbrecciated samples, and they were significantly heavier than the non-Antarctic samples with a d 66 Zn range of +1.63& to +6.22& for four eucrites (mean, +4.32&) and +0.94& to +1.60& for three diogenites (mean + 1.23&), excluding one anomalous sample, while their Zn concentration is significantly lower than the brecciated samples. These data suggest that the unbrecciated eucrites probably represent the eucritic crust shortly after differentiation and cooling of the parent asteroid, at which time volatization of lighter zinc isotopes led to an isotopically heavy crust. Early impact events caused the ejection of these unbrecciated meteorites, which were subsequently spared from brecciation caused by multiple additional impacts on the much larger Vesta. The range of d 66 Zn values and Zn concentration for the brecciated HEDs in this study supports a major contribution to the Vestan surface by chondritic impactors (À1.30 < d 66 Zn < +0.76& for ordinary and carbonaceous chondrites). The anomalous eucrite PCA 82502 (d 66 Zn = À7.75&) is significantly isotopically lighter than the other HEDs and is the natural sample with the lightest Zn isotopic composition reported in the solar system to date. This meteorite most likely originated from a distinct parent body.

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“…Whether the crust formed by serial magmatism or solidification of a magma ocean is unclear. Vesta has experienced significant impact events, one of which excavated a huge (460 km diameter) crater near its south pole [Thomas et al, 1997a]. Spectral variations within this large crater [Thomas et al, 1997b] demonstrate compositional stratigraphy, probably reflecting a mantle and/or lower crust enriched in olivine relative to surficial flows.…”

Section: Vestamentioning

confidence: 99%

“…In the low altitude mapping orbit at altitudes below one body radius, the gravity field is determined up to the 12th degree. With a 12th degree gravity field, correlations with surface features on Vesta of 65 km or greater can be investigated including the large 460 km impact basin near the south pole [Thomas et al, 1997a]. This higher resolution gravity field allows for comparative modeling with lunar impact basins [Zuber et al, 1994].…”

Section: Gravity Sciencementioning

confidence: 99%

“…The latter is a dry, differentiated body whose exterior has been resurfaced by basaltic lava flows possibly possessing an early magma ocean like the Moon. Vesta has experienced significant excavating events, most notably indicated by the huge crater near its southern pole [Thomas et al, 1997a]. Cosmic ray exposure dating of HEDs indicates that impacts have produced meteoritic material at least five times in the last 50 million years [Eugster and Michel, 1995].…”

Section: Introductionmentioning

confidence: 99%

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Dawn: A journey in space and time

Russell¹,

Coradini²,

Christensen³

et al. 2004

Planetary and Space Science

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By successively orbiting both 4 Vesta and 1 Ceres the Dawn mission directly addresses the long-standing goals of understanding the origin and evolution of the solar system. Ceres and Vesta are two complementary terrestrial protoplanets (one apparently "wet" and the other "dry"), whose accretion was probably terminated by the formation of Jupiter. They provide a bridge in our understanding between the rocky bodies of the inner solar system and the icy bodies of the outer solar system. Ceres appears to be undifferentiated while Vesta has experienced significant heating and likely differentiation. Both formed very early in the history of the solar system and while suffering many impacts have remained intact, thereby retaining a record of events and processes from the time of planet formation. Detailed study of the geophysics and geochemistry of these two bodies provides critical benchmarks for early solar system conditions and processes that shaped its subsequent evolution. Dawn provides the missing context for both primitive and evolved meteoritic data, thus playing a central role in understanding terrestrial planet formation and the evolution of the asteroid belt. Dawn is to be launched in May 2006 arriving at Vesta in 2010 and Ceres in 2014, stopping at each to make 11 months of orbital measurements. The spacecraft uses solar electric propulsion, both in cruise and in orbit, to make most efficient use of its xenon propellant. The spacecraft carries a framing camera, visible and infrared mapping spectrometer, gamma ray/neutron spectrometer, magnetometer, and radio science.3

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Impact Excavation on Asteroid 4 Vesta: Hubble Space Telescope Results

Cited by 295 publications

References 29 publications

Lobate and flow-like features on asteroid Vesta

Lobate and flow-like features on asteroid Vesta

Zinc isotopes in HEDs: Clues to the formation of 4-Vesta, and the unique composition of Pecora Escarpment 82502

Dawn: A journey in space and time

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