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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, E08002, doi:10.1029/2004JE002262, 2004

Crustal structure of Mars from gravity and topography

G. A. Neumann

Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
Laboratory for Terrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

M. T. Zuber

Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
Laboratory for Terrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

M. A. Wieczorek

Département de Géophysique Spatiale et Planétaire, Institut de Physique du Globe de Paris, Paris, France

P. J. McGovern

Lunar and Planetary Institute, Houston, Texas, USA

F. G. Lemoine

Laboratory for Terrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

D. E. Smith

Laboratory for Terrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA

Abstract

Mars Orbiter Laser Altimeter (MOLA) topography and gravity models from 5 years of Mars Global Surveyor (MGS) spacecraft tracking provide a window into the structure of the Martian crust and upper mantle. We apply a finite-amplitude terrain correction assuming uniform crustal density and additional corrections for the anomalous densities of the polar caps, the major volcanos, and the hydrostatic flattening of the core. A nonlinear inversion for Moho relief yields a crustal thickness model that obeys a plausible power law and resolves features as small as 300 km wavelength. On the basis of petrological and geophysical constraints, we invoke a mantle density contrast of 600 kg m⁻³; with this assumption, the Isidis and Hellas gravity anomalies constrain the global mean crustal thickness to be >45 km. The crust is characterized by a degree 1 structure that is several times larger than any higher degree harmonic component, representing the geophysical manifestation of the planet's hemispheric dichotomy. It corresponds to a distinction between modal crustal thicknesses of 32 km and 58 km in the northern and southern hemispheres, respectively. The Tharsis rise and Hellas annulus represent the strongest components in the degree 2 crustal thickness structure. A uniform highland crustal thickness suggests a single mechanism for its formation, with subsequent modification by the Hellas impact, erosion, and the volcanic construction of Tharsis. The largest surviving lowland impact, Utopia, postdated formation of the crustal dichotomy. Its crustal structure is preserved, making it unlikely that the northern crust was subsequently thinned by internal processes.

Received 9 March 2004; accepted 11 June 2004; published 10 August 2004.

Keywords: crustal dichotomy; impact basins; Martian crust.

Index Terms: 1227 Geodesy and Gravity: Planetary geodesy and gravity (5420, 5714, 6019); 5420 Planetology: Solid Surface Planets: Impact phenomena (includes cratering); 5410 Planetology: Solid Surface Planets: Composition; 5415 Planetology: Solid Surface Planets: Erosion and weathering; 5430 Planetology: Solid Surface Planets: Interiors (8147).

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Citation: Neumann, G. A., M. T. Zuber, M. A. Wieczorek, P. J. McGovern, F. G. Lemoine, and D. E. Smith (2004), Crustal structure of Mars from gravity and topography, J. Geophys. Res., 109, E08002, doi:10.1029/2004JE002262.

Copyright 2004 by the American Geophysical Union.