2007
G.K. Gilbert Award

Maria T. Zuber
Massachusetts Institute of Technology

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All 2007
Division Award Recipients

Presented to Maria T. Zuber

 Citation by Sean C. Solomon

More than any other individual in planetary science, Maria Zuber has pioneered the measurement and interpretation of the shapes of the surfaces of the inner planets, small bodies, and satellites and what those shapes mean for internal structure and dynamics, thermal and magmatic history, and surface-atmosphere interactions. What stand her apart are her combination of important theoretical contributions and expertise in the development of spacecraft experiments as well as the analysis of the derived data sets. Through her space mission leadership, she has advanced substantially our understanding of the internal structure and evolution of the Moon, Mars, and asteroids.

Maria’s earliest work was in planetary tectonics, notably her development of the idea that many tectonic features arise from instabilities in the lithosphere induced by in-plane or basal shear stress and that the mechanical properties of the lithosphere may be inferred from the characteristics (particularly the wavelengths) of these instabilities. Together with colleagues and students she developed a suite of mathematical models to explore this hypothesis, and she persuasively applied the models to problems as diverse as extension in the Basin and Range Province, lithospheric shortening in the central Indian Ocean basin, rift systems on Earth and Venus, and the formation of wrinkle ridges on Mars and ridge belts on Venus. More recent work by Maria and her group has included numerical and laboratory analogue models of fault development that combine failure criteria, models of stress and strain, and observations of fault distributions and geometry in a variety of planetary settings. This body of work sets on a firm quantitative basis the interpretation of many classes of tectonic features on the terrestrial planets.

Maria led the data reduction and analysis efforts of the laser ranging experiment team on the Clementine mission that produced the first global topographic map of the Moon. From that work, in combination with a newly determined lunar gravity field, she produced the first global model of lunar crustal structure. It is difficult to overstate the importance of that work. The new models changed our understanding of the extent of isostatic compensation in the early history of the Moon, particularly during the formation and later modification of large impact basins. More importantly, they elucidated for the first time the strongly aspherical nature of internal temperature and melt production in the lunar mantle. Before Maria’s work, the preferential location of lunar mare basalt deposits on the nearside of the Moon was attributed to a crust on the farside that was sufficiently thick that mare basalt magmas could not rise buoyantly to the surface. The Clementine altimetry and crustal thickness model, to the contrary, showed that the crust beneath the farside South Pole-Aitken basin is thinner than beneath much of the nearside, yet the basin is comparatively free of mare basalt deposits. The origin of this nearside-farside difference in lunar evolution remains a very active research issue.

As Deputy Principal Investigator for the Mars Orbital Laser Altimeter (MOLA) on the Mars Global Surveyor (MGS) spacecraft, Maria shares much of the credit (along with Principal Investigator David Smith) for the superb topographic data that have been returned by that instrument. As a result of MOLA observations, we now know the topography of Mars better than we do for any other planet (including Earth). More importantly, the data have stimulated a new understanding of a host of phenomena that affect the Martian surface, from cratering and deformation, to volcanism and atmospheric circulation, to the erosional and depositional action of water and ice. Maria led the combined interpretation of MOLA topography and the MGS-derived gravity field to produce the first high-resolution global determination of crustal thickness on Mars. Her crustal thickness models showed that Mars can be divided into two approximately hemispherical provinces, a southern province dominated by a progressive thinning of the crust from south to north, and a northern province of approximately uniform crustal thickness. These results constitute key constraints on the formation and modification of the Martian crust and are fueling a bevy of follow-on studies by the planetary geology and geophysics community.

As the leader of the Laser Rangefinder experiment on the Near Earth Asteroid Rendezvous (NEAR) Shoemaker mission, Maria produced the first detailed three-dimensional view of the shape of an asteroid (433 Eros). From the volume and mass of the asteroid has come the first precise estimate of mean density (2.67 ± 0.03 Mg/m3). From the ordinary chondritic composition inferred from visible–near-infrared and X-ray spectral information, a mean porosity of 10-30% has been inferred. The laser rangefinding results also resolved an offset between centers of figure and mass, evidence for a competent substrate from regional-scale relief and slope, and small-scale ridges and grooves thought to be the result of fracturing during impacts.

More recently Maria has employed MOLA data to understand seasonal and interannual climate change on Mars. In a major tour de force she extracted from altimetry data the extremely small (meter to sub-meter) changes in the latitude-dependent elevation of polar regions and showed how those changes correlated with seasonal variations in the planet’s gravitational oblateness and the changes expected from atmospheric circulation and CO2 exchange models.

Beyond her towering research accom-plishments, Maria’s many contributions to the planetary science community include service as President of the American Geophysical Union’s Planetary Sciences Section from 1998 to 2000 and membership on the 2004 President’s Commission on Implementation of U.S. Space Exploration Policy. She is currently the Deputy PI on the Lunar Orbiter Laser Altimeter on the Lunar Reconnaissance Orbiter, the Team Leader for the Radio Science Gravity Investigation on the Mars Reconnaissance Orbiter, and the Chair of the Geophysics Discipline Group for the MESSENGER mission to Mercury.

On the basis of her seminal studies of the internal structure of the Moon, Mars, and Eros; her broadly influential theoretical work on the interpretation of planetary tectonic features; and her myriad contributions to the planetary science community, Maria Zuber is an exceptionally worthy recipient of the Planetary Geology Division’s Grove Karl Gilbert Award for 2007.

  2007 G.K. Gilbert Award - Response by Maria T. Zuber

I would like to thank the Planetary Geology Division of GSA for presenting me with the G.K. Gilbert Award, and also my nominators and letter writers for investing their precious time on my behalf. I am greatly honored and more than a little humbled. Most people undergo treatment for their addictions, and I am being rewarded for mine.

Occasions like this provide a time for reflection, about how one reaches the point where one finds oneself. In my case there was little doubt that I would pursue a career in space science. From as early as I can remember I was fascinated by space, reading every book in sight, and spending hours upon hours observing the night sky. People would ask how I got interested in this field and I concluded after some time that the answer is: genetics.

My first inspiration was my grandfather, George Stoffa, with whom I spent much of my time growing up building and using telescopes. I used to wonder whether he was really interested in astronomy or just did it to help me. But I eventually learned the truth. He quit school in eighth grade to work in the mines to support his family, but with the little money that he was allowed to keep he saved and bought a telescope. For much of his life he spent his days inside the Earth but his nights in space. I’ve concluded there is a recessive gene in my family that programs the holder to explore the universe. Sometimes I think about what hasn’t been discovered yet because my grandfather never had the educational opportunities that I did.

In my more formal education I have been truly blessed to have mentors and colleagues who bent over backwards to provide me with great opportunities coupled with high expectations that drove me to achieve things beyond what could rationally be imagined. Marc Parmentier taught me problem solving and critical analysis and remains a trusted colleague and collaborator. Dave Smith gave me the opportunity to work on my first mission and we have gone on to map much of the inner solar system; he deserves credit for transforming planetary cartography into a precise geodetic science that has made myriads of discoveries possible. He, Greg Neumann, Frank Lemoine and others produced such remarkable data sets that it has been possible to advance the state of the art by leaps and bounds. Sean Solomon gets most of the credit for pushing me to think in terms of the big picture, and along with Roger Phillips, Jim Head and many other scientific collaborators on the various missions on which I have worked helped me to tackle the right problems from every conceivable angle.

I also owe a great deal of thanks to my students and post docs, who usually wind up teaching me as much as I have taught them. That so many of them are on the path to having spectacularly successful careers of their own is my proudest professional achievement. I also express my gratitude to the many engineers with whom that I have worked. Their brilliance and attention to detail has turned dreams into reality.

Finally, I would like to thank my family. Neither of my parents attended college and they couldn’t understand why anyone would want to stay in school as long as I did. But they have helped and supported me every step of the way and deserve much of the credit for any success that has come to me. I could not have accomplished even a fraction of what I have without my husband, Jack Mizerak; he has been a dedicated partner and father while building a successful career of his own, and he has taught me the importance of balance. My boys, Jack and Jordan, have helped me keep life in perspective. Every time I would come home and report that I’d won another instrument proposal they would cheer about another trip to Disney World. There’s nothing better in life than to be in a situation where everybody wins.