Mark Wieczorek's Home Page

HOME CURRICULUM VITAE PUBLICATIONS RESEARCH

Research Interests

Planetary missions

I am currently participating in the following planetary missions:

Gravity and topography analyses

One manner in which the interior structure of a planet can be investigated is through the joint analysis of its gravitational field and topography. Detailed gravity and topography models are now available for the Earth, Moon, Mars and Venus, and most analyses of these data have focussed on elucidating the structure of both the crust and lithosphere. As examples, global crustal thickness maps have been constructed, and for the Moon and Mars, these have led to a better understanding of giant impact events. The densities of the major Martian volcanoes have been estimated, and these have been found to be consistent with the compositions of the basaltic Martian meteorites. In addition, the elastic thickness has been estimated at various locals on these planetary bodies, and this places constraints on how the heat flow has varied both in space and time.

Animation showing the Moon's topography, gravity, and crustal thickness.

Crustal thickness of the Moon. This animation shows the Moon's topography, radial gravity, and modeled crustal thickness. In this global Mollweide projection, the near-side hemisphere is on the right, and the far-side hemisphere is on the left. Many circular impact basins are visible as topographic depressions that possess positive gravity anomalies and a thinned crust. See Wieczorek and Phillips (1998, 1999), Wieczorek et al. (2006), and Wieczorek (2008).


Localized spectral analysis

It is common to express data on the sphere in spherical harmonic basis functions and to use their spectral properties to make inferences about the underlying process. For example, the cross-power spectra of gravity and topography can be used to invert for the elastic thickness, crustal thickness, and crustal density, the power spectrum of a planet's magnetic field depends upon the depth of magnetic sources, and the power spectrum of the cosmic microwave background radiation is dependent upon several parameters, such as the matter density of the universe and Hubble constant.

In many cases it is necessary to estimate the spectral properties of a process either in a specific region or by using only a subset of the full data set. This can be done by multiplying the data by one or several specially constructed localization windows, or by the convolution with spherical wavelets. The discipline of spectral analysis on the sphere is young, and the continued application of these techniques to real data are bound to yield many surprises.

Slepian windows on the sphere

Localization windows on the surface of a sphere: The first 16 orthogonal windows whose spatial power is optimally concentrated within a spherical cap of angular radius 30° (dotted circle), and yet bandlimited to a maximum spherical harmonic degree of L=29. Each non-zonal window possesses a twin that is rotated by m/90°. λ indicates the power of the function within the spherical cap divided by the total power of the function. See Wieczorek and Simons (2005, 2007) and Simons et al. (2006).


Impact cratering

Impact cratering is one of the major geologic processes that has affected the terrestrial planets. However, as a result of plate tectonics and weather on Earth, it is necessary to turn to other planetary bodies, such as the Moon and Mars, to investigate the processes associated with the largest impacts events (from 10s to 1000s of kilometers in diameter). Geophysical modeling on the Moon has been able to constrain both the diameter and depth of excavation of the giant multiring basins, and in some cases, these models predict that the mantle might even have been excavated.

Impact cratering is also an indispensable tool for dating planetary surfaces. The crater chronology method was originally developed for the Moon and calibrated in an absolute sense by the Apollo and Luna samples. Nevertheless, recent studies show that some of the fundamental assumptions of the crater chronology method are not entirely valid. As an example, the impact flux on the lunar surface is now known not to be independent of position. The Moon's synchronous rotation gives rise to a higher impact flux on its western hemisphere, and the ecliptic distribution of near Earth asteroids causes fewer impacts to occur near the poles.

Thermal evolution of the Moon

The first pictures of the Moon's far side hemisphere that were taken in 1959 showed us that the majority of the dark "mare" (vast flood basaltic lava plains) are located on the Moon's Earth-facing hemisphere. While many hypotheses had been advanced for this observation, it was not until the Lunar Prospector gamma-ray spectrometer mapped the surface distribution of heat producing elements (thorium, uranium, and potassium) that the true cause of this phenomena began to be understood.

These data demonstrate that a large portion of the Moon's heat producing elements (which are part of the geochemical component KREEP, for potassium, rare Earth elements, and phosphorous) is located in a single near-side geochemical province, now referred to as the Procellarum KREEP terrane. The enhanced heat production in this province somehow led to melting of the underlying mantle, accounting for the majority of the Moon's basaltic eruptions. One model predicts that the current heat flow could be a factor of three larger in this terrane than in the more representative feldspathic highlands. This hypothesis seems to be consistent with the Apollo heat flow measurements that were made on the rims of the Imbrium and Serenitatis impact basins.


Distribution of thorium on the lunar surface

Distribution of thorium on the Moon's surface: Gamma-ray spectroscopy data show that a large portion of the Moon's thorium, and by inference KREEP, is concentrated in a single geochemical province on the Moon's near-side hemisphere. The enhanced heat production of this province is somehow responsible for the prevalence of basaltic eruptions in this region. See Wieczorek and Phillips (2000), Jolliff et al. (2000), and Wieczorek et al. (2006).

> Home

Centre National de la Recherche Scientifique Institut de Physique du Globe de Paris © 2008 Mark Wieczorek