The Crust of the Moon as Seen by GRAIL

The Holy GRAIL? The gravity field of a planet provides a view of its interior and thermal history by revealing areas of different density. GRAIL, a pair of satellites that act as a highly sensitive gravimeter, began mapping the Moon's gravity in early 2012. Three papers highlight some of the results from the primary mission. Zuber et al. (p. 668, published online 6 December) discuss the overall gravity field, which reveals several new tectonic and geologic features of the Moon. Impacts have worked to homogenize the density structure of the Moon's upper crust while fracturing it extensively. Wieczorek et al. (p. 671, published online 6 December) show that the upper crust is 35 to 40 kilometers thick and less dense—and thus more porous—than previously thought. Finally, Andrews-Hanna et al. (p. 675, published online 6 December) show that the crust is cut by widespread magmatic dikes that may reflect a period of expansion early in the Moon's history. The Moon's gravity field shows that the lunar crust is less dense and more porous than was thought. High-resolution gravity data obtained from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft show that the bulk density of the Moon's highlands crust is 2550 kilograms per cubic meter, substantially lower than generally assumed. When combined with remote sensing and sample data, this density implies an average crustal porosity of 12% to depths of at least a few kilometers. Lateral variations in crustal porosity correlate with the largest impact basins, whereas lateral variations in crustal density correlate with crustal composition. The low-bulk crustal density allows construction of a global crustal thickness model that satisfies the Apollo seismic constraints, and with an average crustal thickness between 34 and 43 kilometers, the bulk refractory element composition of the Moon is not required to be enriched with respect to that of Earth.

[1]  H. Henkel,et al.  The extent of impact induced fracturing from gravity modeling of the Granby and Tvaren simple craters , 2010 .

[2]  D. Breuer,et al.  Influence of a variable thermal conductivity on the thermochemical evolution of Mars , 2006 .

[3]  M. Wieczorek,et al.  Crustal thickness of the Moon: New constraints from gravity inversions using polyhedral shape models , 2007 .

[4]  Harold F. Levison,et al.  An Archaean heavy bombardment from a destabilized extension of the asteroid belt , 2012, Nature.

[5]  R. Clayton,et al.  Geochemistry, petrology and ages of the lunar meteorites Kalahari 008 and 009: New constraints on early lunar evolution , 2008 .

[6]  J. Ashby.  References and Notes , 1999 .

[7]  Remo Guidieri.  Res , 1995, RES: Anthropology and Aesthetics.

[8]  D. Healy,et al.  Computing Fourier Transforms and Convolutions on the 2-Sphere , 1994 .

[9]  Erwan Mazarico,et al.  Lunar impact basins: Stratigraphy, sequence and ages from superposed impact crater populations measured from Lunar Orbiter Laser Altimeter (LOLA) data , 2012 .

[10]  Roger J. Phillips,et al.  Potential anomalies on a sphere: Applications to the thickness of the lunar crust , 1998 .

[11]  T. Hiroi,et al.  Asymmetric crustal growth on the Moon indicated by primitive farside highland materials , 2012 .

[12]  Colin Tudge,et al.  Planet , 1999 .

[13]  P. Warren.  “New” lunar meteorites: Implications for composition of the global lunar surface, lunar crust, and the bulk Moon , 2005 .

[14]  G. Kallemeyn,et al.  “New” lunar meteorites: Impact melt and regolith breccias and large‐scale heterogeneities of the upper lunar crust , 2005 .

[15]  Andrew G. Glen,et al.  APPL , 2001 .

[16]  M. Ćuk,et al.  Making the Moon from a Fast-Spinning Earth: A Giant Impact Followed by Resonant Despinning , 2012, Science.

[17]  R. J. Willemann,et al.  Role of membrane stresses in the support of planetary topography , 1981 .

[18]  S. Jain,et al.  Earth as a Planet , 2014 .

[19]  Paul G. Lucey,et al.  Compositional variations of the lunar crust: Results from radiative transfer modeling of central peak spectra , 2009 .

[20]  David E. Smith,et al.  The lunar crust: Global structure and signature of major basins , 1996 .

[21]  R. Korotev,et al.  Feldspathic lunar meteorites Pecora Escarpment 02007 and Dhofar 489 : Contamination of the surface of the lunar highlands by post-basin impacts , 2006 .

[22]  48 , 2015, Slow Burn.

[23]  R. Korotev,et al.  Mineralogy, geochemistry, and 40Ar–39Ar geochronology of lunar granulitic breccia Northwest Africa 3163 and paired stones: Comparisons with Apollo samples , 2011 .

[24]  Janusz Eluszkiewicz,et al.  Dim prospects for radar detection of Europa's ocean , 2004 .

[25]  D. Kring,et al.  Northwest Africa 482: A crystalline impact‐melt breccia from the lunar highlands , 2002 .

[26]  G. Dresen,et al.  Dislocation and diffusion creep of synthetic anorthite aggregates , 2000 .

[27]  Harold Jeffreys,et al.  On the Structure of the Moon , 1967 .

[28]  R. Korotev.  Lunar meteorites from Oman , 2012 .

[29]  David E. Smith,et al.  Gravity Field of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL) Mission , 2013, Science.

[30]  R. Pappalardo,et al.  On the origins of band topography, Europa , 2003 .

[31]  G. J. Taylor,et al.  Lunar composition: A geophysical and petrological synthesis , 1988 .

[32]  R. Canup.  Forming a Moon with an Earth-like Composition via a Giant Impact , 2012, Science.

[33]  P. Lognonné,et al.  Very preliminary reference Moon model , 2011 .

[34]  J. Maclennan,et al.  Joint inversion of seismic and gravity data for lunar composition and thermal state , 2007 .

[35]  D. Britt,et al.  The density and porosity of lunar rocks , 2012 .

[36]  R. Pepin,et al.  Impact and explosion cratering : planetary and terrestrial implications : proceedings of the Symposium on Planetary Cratering Mechanics, Flagstaff, Arizona, September 13-17, 1976 , 1977 .

[37]  T. Hiroi,et al.  Massive layer of pure anorthosite on the Moon , 2012 .

[38]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[39]  D. Britt,et al.  Analysis of systematic error in “bead method” measurements of meteorite bulk volume and density , 2010 .

[40]  David E. Smith,et al.  The Shape and Internal Structure of the Moon from the Clementine Mission , 1994, Science.

[41]  R. Smoluchowski.  Amorphous ice and the behavior of cometary nuclei , 1981 .

[42]  R. Ostertag,et al.  Rock 61016 - Multiphase shock and crystallization history of a polymict troctolitic-anorthositic breccia , 1975 .

[43]  Andrew C. Fowler,et al.  A mathematical model of magma transport in the asthenosphere , 1985 .

[44]  Klaus Mosegaard,et al.  An inquiry into the lunar interior: A nonlinear inversion of the Apollo lunar seismic data , 2002 .

[45]  A. Heuer,et al.  The thermal and deformational history of apollo 15418, A partly shock-melted lunar breccia , 1977 .

[46]  David E. Smith,et al.  Gravity Recovery and Interior Laboratory (GRAIL): Mapping the Lunar Interior from Crust to Core , 2013, Space Science Reviews.

[47]  Ralph B. Roncoli,et al.  GRAIL Trajectory Design: Lunar Orbit Insertion through Science , 2010 .

[48]  F. Simons,et al.  Localized spectral analysis on the sphere , 2005 .

[49]  G. Ryder.  Lunar anorthosite 60025, the petrogenesis of lunar anorthosites, and the composition of the Moon , 1982 .

[50]  M. Nafi Toksöz,et al.  Structure of the Moon , 1974 .

[51]  Patrick Wu,et al.  Rheology of the Upper Mantle: A Synthesis , 1993, Science.

[52]  Hiroshi Araki,et al.  Crustal thickness of the Moon: Implications for farside basin structures , 2009 .

[53]  R. Korotev,et al.  Compositional and lithological diversity among brecciated lunar meteorites of intermediate iron concentration , 2009 .

[54]  Qinghui Liu,et al.  An improved lunar gravity field model from SELENE and historical tracking data: Revealing the farside gravity features , 2010 .

[55]  M. Wieczorek,et al.  Lateral variations of lunar crustal thickness from the Apollo seismic data set , 2006 .

[56]  Stephen M. Clifford,et al.  A model for the hydrologic and climatic behavior of water on Mars , 1993 .

[57]  T. Spohn,et al.  A seismic model of the lunar mantle and constraints on temperature and mineralogy , 2006 .

[58]  David E. Smith,et al.  Ancient Igneous Intrusions and Early Expansion of the Moon Revealed by GRAIL Gravity Gradiometry , 2013, Science.

[59]  Philippe Lognonné,et al.  A new seismic model of the Moon: implications for structure, thermal evolution and formation of the Moon , 2003 .

[60]  David E. Smith,et al.  Initial observations from the Lunar Orbiter Laser Altimeter (LOLA) , 2010 .

[61]  David J. Heather,et al.  New views of the Moon , 1999 .

[62]  R. Korotev.  Lunar geochemistry as told by lunar meteorites , 2005 .

[63]  R. Roncoli,et al.  Mission Design Overview for the Gravity Recovery and Interior Laboratory (GRAIL) Mission , 2010 .

[64]  Guy J. Consolmagno,et al.  The significance of meteorite density and porosity , 2008 .

[65]  Frederik J. Simons,et al.  Minimum-Variance Multitaper Spectral Estimation on the Sphere , 2007, 1306.3254.

[66]  K. Rasmussen,et al.  Megaregolith insulation, internal temperatures, and bulk uranium content of the moon , 1987 .

[67]  G. J. Taylor,et al.  The Moon: A Taylor perspective , 2005 .

[68]  A. Konopliv,et al.  Recent Gravity Models as a Result of the Lunar Prospector Mission , 2001 .

[69]  Thomas H. Prettyman,et al.  Elemental composition of the lunar surface: Analysis of gamma ray spectroscopy data from Lunar Prospector , 2006 .

[70]  Satoru Yamamoto,et al.  Possible mantle origin of olivine around lunar impact basins detected by SELENE , 2010 .

[71]  M. Wieczorek,et al.  Gravity and Topography of the Terrestrial Planets , 2015 .

[72]  L. Pesonen,et al.  Physical properties of the Yaxcopoil‐1 deep drill core, Chicxulub impact structure, Mexico , 2011 .

[73]  O. Kuskov,et al.  Constitution of the Moon: 5. Constraints on composition, density, temperature, and radius of a core , 1998 .

[74]  Kaare Lund Rasmussen,et al.  A new seismic velocity model for the Moon from a Monte Carlo inversion of the Apollo lunar seismic data , 2000 .

[75]  Mark A. Wieczorek,et al.  Spatiospectral Concentration on a Sphere , 2004, SIAM Rev..

[76]  M. Wieczorek,et al.  Density and porosity of the lunar crust from gravity and topography , 2012 .

[77]  C. Floss,et al.  Petrogenesis of lunar highlands meteorites: Dhofar 025, Dhofar 081, Dar al Gani 262, and Dar al Gani 400 , 2004 .

[78]  J. J. Gillis,et al.  Feldspathic lunar meteorites and their implications for compositional remote sensing of the lunar surface and the composition of the lunar crust , 2003 .