The Crust of the Moon as Seen by GRAIL

Wieczorek, M. A.; Neumann, Gregory A.; Nimmo, F.; Kiefer, W. S.; Taylor, G. J.; Melosh, H. J.; Phillips, R. J.; Solomon, Sean C.; Andrews-Hanna, J. C.; Asmar, S. W.; Konopliv, Alexander S.; Lemoine, F. G.; Smith, David E.; Watkins, M. M.; Williams, J. G.; Zuber, M. T.

doi:10.1126/science.1231530

Cited by 798 publications

(1,135 citation statements)

References 70 publications

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“…This is consistent with Leeuwenhoek's location outside of the SPA transient cavity as well as the estimated depth of origin of Leeuwenhoek's peak materials (~20 km), which is less than the crustal thickness in the region as estimated by GRAIL [Spudis, 1993;Petro and Pieters, 2002;Potter et al, 2012;Wieczorek et al, 2013].…”

Section: Plagioclase and Orthopyroxene In Leeuwenhoeksupporting

confidence: 75%

“…On average, the crust is~40 km thick, as shown by recent models incorporating Gravity Recovery and Interior Laboratory (GRAIL) gravity and Lunar Orbiter Laser Altimeter (LOLA) topography data [Wieczorek et al, 2013]. Several lines of evidence from lunar sample analyses as well as remote sensing studies suggest that the mafic content of the crust increases with depth [Reid et al, 1977;Ryder and Wood, 1977;Bussey and Spudis, 2000;Tompkins and Pieters, 1999;Cahill et al, 2009;Ohtake et al, 2009].…”

Section: The Evolution and Stratigraphy Of The Lunar Crust And Mantlementioning

confidence: 98%

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Compositional heterogeneity of central peaks within the South Pole‐Aitken Basin

2013

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[1] Using high-spectral and -spatial resolution Moon Mineralogy Mapper data, we investigate compositional variations across the central peak structures of four impact craters within the South Pole-Aitken Basin (SPA). Two distinct causes of spectral diversity are observed. Spectral variations across the central peaks of Bhabha, Finsen, and Lyman are dominated by soil development, including the effects of space weathering and mixing with local materials. For these craters, the central peak structure is homogeneous in composition, although small compositional differences between the craters are observed. This group of craters is located within the estimated transient cavity of SPA, and their central uplifts exhibit similar mafic abundances. Therefore, it is plausible that they have all uplifted material associated with melts of the lower crust or upper mantle produced during the SPA impact. Compositional differences observed between the peaks of these craters reflect heterogeneities in the SPA subsurface, although the origin of this heterogeneity is uncertain. In contrast to these craters, Leeuwenhoek exhibits compositional heterogeneity across its central peak structure. The peak is areally dominated by feldspathic materials, interspersed with several smaller exposures exhibiting a mafic spectral signature. Leeuwenhoek is the largest crater included in the study and is located in a region of complex stratigraphy involving both crustal (feldspathic) and SPA (mafic melt and ejecta) materials. The compositional diversity observed in Leeuwenhoek's central peak indicates that kilometer-scale heterogeneities persist to depths of more than 10 km in this region.

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Section: Plagioclase and Orthopyroxene In Leeuwenhoeksupporting

confidence: 75%

Section: The Evolution and Stratigraphy Of The Lunar Crust And Mantlementioning

confidence: 98%

Compositional heterogeneity of central peaks within the South Pole‐Aitken Basin

2013

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“…This finding might have implications for a number of studies that calculate or estimate the porosity reduction of a porous layer and only consider the lithostatic pressure for compaction (e.g. Wieczorek et al 2013;Nimmo et al 2003;Fu & Elkins-Tanton 2014). The timescale of the porosity loss t comp varies in our calculations between O(0.1 Ma) and O(10 Ma) (see Table 3), which argues against assumptions of fixed compaction timescales utilised in some planetesimal studies.…”

Section: Summary and Discussioncontrasting

confidence: 38%

Modelling of compaction in planetesimals

Neumann

Breuer

Spohn

2014

A&A

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Aims. Compaction of initially porous material prior to melting is an important process that has influenced the interior structure and the thermal evolution of planetesimals in their early history. On the one hand, compaction decreases the porosity resulting in a reduction of the radius and on the other hand, the loss of porosity results in an increase of the thermal conductivity of the material and thus in a more efficient cooling. Porosity loss by hot pressing is the most efficient process of compaction in planetesimals and can be described by creep flow, which depends on temperature and stress. Hot pressing has been repeatedly modelled using a simplified approach, for which the porosity is gradually reduced in some fixed temperature interval between ≈650 K and 700 K. This approach neglects the dependence of compaction on stress and other factors such as matrix grain size and creep activation energy. In the present study, we compare this parametrised method with a self-consistent calculation of porosity loss via a creep related approach. Methods. We use our thermal evolution model from previous studies to model compaction of an initially porous body and consider four basic packings of spherical dust grains (simple cubic, orthorhombic, rhombohedral, and body-centred cubic). Depending on the grain packing, we calculate the effective stress and the associated porosity change via the thermally activated creep flow. For comparison, compaction is also modelled by simply reducing the initial porosity linearly to zero between 650 K and 700 K. As we are interested in thermal metamorphism and not melting, we only consider bodies that experience a maximum temperature below the solidus temperature of the metal phase. Results. For the creep related approach, the temperature interval in which compaction takes place depends strongly on the size of the planetesimal and is not fixed as assumed in the parametrised approach. Depending on the radius, the initial grain size, the activation energy, and the initial porosity and specific packing of the dust grains, the temperature interval lies within 500−1000 K. This finding implies that the parametrised approach strongly overestimates compaction and underestimates the maximum temperature. For the cases considered, the post-compaction porous layer retained at the surface is a factor of 1.5 to 4 thicker for the creep related approach. The difference in the temperature evolution between the two approaches increases with decreasing radius and the maximum temperature can deviate by over 30% for small bodies.

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“…13a-d and in Table 1. The grey region for the Moon is the same in all panels, and assumes an impact velocity of 17.5 km/s, with the lower bound given by 0% porosity and the upper bound by 20% porosity (the latest results from the GRAIL mission place the average lunar crustal porosity at 12%, Wieczorek et al, 2013). Vertical impacts are assumed in all cases.…”

Section: Results Ii: Modeling Impact Melts On Vestamentioning

confidence: 99%

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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The Crust of the Moon as Seen by GRAIL

Cited by 798 publications

References 70 publications

Compositional heterogeneity of central peaks within the South Pole‐Aitken Basin

Compositional heterogeneity of central peaks within the South Pole‐Aitken Basin

Modelling of compaction in planetesimals

Lobate and flow-like features on asteroid Vesta

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