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2010 Barringer Medal for William K. Hartmann

2010; Wiley; Volume: 45; Issue: 7 Linguagem: Inglês

10.1111/j.1945-5100.2010.01112.x

1945-5100

C. R. Chapman,

Space Exploration and Technology

I am pleased to introduce William K. Hartmann, who is the 2010 awardee of the Meteoritical Society’s Barringer Medal, sponsored by the Barringer Crater Company. I first met Bill at an amateur astronomy conference in 1960. A couple of years later, he recommended me for a summer job—measuring lunar craters—to Gerard Kuiper, who had recently founded the Lunar and Planetary Laboratory at the University of Arizona. Bill was, at that time, already deeply involved in researching craters, the theme of his scientific career ever since. Indeed, by the time I arrived at the Lunar Lab fresh out of high school, he had already made one of his seminal discoveries. In 2010, it seems remarkable that someone could actually have “discovered” the multi-ring Orientale basin on the Moon. Bill Hartmann was the discoverer and he actually coined the word “basin” to name his new gestalt, which distinguishes the concentric structures from the low-albedo mare units within many basins. We now know Orientale to be the last of the great lunar basins formed during the decline of the Late Heavy Bombardment and, as such, it has become the archetype of solar system impact basins. Telescopic observers had long known of “Mare Orientale” and the associated “Cordillera Mountains” on the east limb of the Moon, but it was not until Bill Hartmann and his colleagues rectified telescopic photographs by projecting them onto a large white globe, that he recognized five nested rings and analyzed them in the context of 11 other lunar basins, as described in Volume 1 of the “Communications of the Lunar and Planetary Laboratory.” Bill completed his Ph.D. thesis, “The History of the Lunar Surface,” in 1965 and was the first to analyze Dai Arthur’s lunar crater catalog, “The System of Lunar Craters,” which I had been hired to work on. These studies led to Bill’s first two publications in Icarus and to his being selected as co-recipient of the 1964/1965 Nininger Meteorite Award; his topic was “Terrestrial and Lunar Flux of Large Meteorites Through the Solar System History.” Throughout his career, Bill Hartmann has had the gift of having insights that have proven correct, even though his arguments sometimes seemed based more on intuitive plausibility than on rigorous logic. One of the most profound of these was Bill’s conclusion, published in several papers in 1965 and 1966, years before a robust lunar chronology was developed from Apollo samples, that there was what he termed an “Early Intense Bombardment” of the Moon. While such an idea was not new, there was intense debate and much uncertainty about the lunar chronology as the Apollo landings approached. Bill’s confidently worded 1966 abstract begins, “During the first seventh of lunar history, the cratering rate on the Moon averaged roughly 200 times the average post-mare rate.” While those words seem very reasonable now, such luminaries as Gene Shoemaker, Don Gault, and Ralph Baldwin thought differently before the Apollo landings. Concerning Bill’s inference that the maria were about 3.5 Gyr old, Don Wilhelms has written, “I have always thought that Bill has led a charmed life, although he may be just plain smart.” Figure 5 of Bill’s 1966 paper “Early Lunar Cratering” may be the first graphical depiction of an early spike in the lunar cratering rate, followed by a low, constant cratering rate continuing to the present. Indeed, this diagram is ironic inasmuch as Bill later became one of the most outspoken skeptics about whether a spike-like Late Heavy Bombardment (or terminal cataclysm) ever happened. He has been inclined to interpret evidence for a spike in the cratering rate as artifacts. Another vital Hartmann contribution to lunar science came on August 20, 1974, when, in Clark Hall at Cornell University, Bill and his colleague Don Davis presented a short, 8-minute contributed talk in which they discussed how a second-largest “satellite-sized” body left over after planetary accretion might be large enough, among other things, to have formed the Earth’s Moon by collision with the Earth. Their work, entitled “Satellite-Sized Planetesimals and Lunar Origin,” was published in spring 1975. Within a decade, after the model was further developed by Al Cameron, Bill Ward, George Wetherill, and others, a consensus developed at a conference on lunar origin held in Kona, Hawaii, that the Moon was formed by such a giant impact (Bill co-edited and wrote the preface to the book Origin of the Moon that resulted from this conference). There are serious issues with the giant impact model of lunar origin, but it still remains the consensus that it is better than any other model. Bill Hartmann has written many important papers over the years, almost always on themes concerning craters, the asteroids and comets that do the cratering, and the fragmental outcomes of hypervelocity impacts. Using down-to-earth approaches to qualitative understanding of cratering processes, Bill has been more apt to gain insights from simple back-yard experiments, visualizations, and graphical plots of zeroth-order data rather than by using expensive gas-gun equipment or computers. In the 1960s, he published important papers on the size distributions of terrestrial craters and of rock fragments of all sorts, as well as secondary craters made by such fragments. As a member of the Mariner 9 imaging team, Bill intensively researched the Martian cratering record and he continues to study Martian craters today. In the 1980s, Bill led a team of 11 scientists, as part of the Basaltic Volcanism Study Project, to research the cratering chronologies (both relative and absolute) of the younger planetary surfaces; that report is still referred to today. Since then, Bill Hartmann has been a chief leader in attempts to systematize Martian crater counts to determine relative ages (and model absolute ages) of geological units on Mars by developing and revising his “Hartmann Production Function.” An essential concept he developed was his mid-1980s demonstration that the near-equivalence of spatial densities of craters on the most densely cratered regions on planets and satellites meant that the crater populations were reaching an equilibrium due to crater-upon-crater saturation. Bill Hartmann has been prescient in many ways. For decades, he has emphasized the theme that there are more similarities among asteroids and comets than differences. Only during the last decade has this perspective become well substantiated with the discovery of main-belt comets, icy asteroids, and so on. In 1978, long before discovery of the first asteroidal satellite, binary asteroid, or contact binary—now known to characterize nearly a third of asteroids—Bill depicted a model (developed by himself and Dale Cruikshank) of the Trojan asteroid Hektor as a contact binary, resulting from the low-velocity collision of two separate planetesimals. This remains the best model for Hektor today, although it is possible that it is actually a close binary. Of course, people who know Bill Hartmann realize that scientific research has been just one facet of his diverse interests and activities. Bill’s 1972 textbook, Moons and Planets, was the first text to infuse many planetary topics with the theme of impacts, a perspective then developing from the “golden age” of spacecraft exploration (the latest edition came out in 2004). In the 1990s, Bill developed an often praised grades 6–12 educational module of 20 laboratory exercises for the National Science Teachers of America entitled “Craters! A Multi-Science Approach to Cratering and Impacts.” Bill is also a well-known author of popular books and is an internationally recognized space artist. Impact cratering and catastrophic collisions among small bodies frequently appear in these works. Given his scientific expertise and intuitive sense of physical realism, Bill’s artwork has often helped his colleagues to visualize the implications of their theoretical research. An example is Bill’s early 1980s painting of “Dynamic Ephemeral Bodies” in Saturn’s rings, which depicts the larger objects within the rings that are constantly interacting and changing, behavior that he and his colleagues had theorized about in technical papers. With Cassini now studying thousands of bodies or concentrated structures in the rings, Bill’s vision from a quarter century ago seems as good and reasonable today as it was new and controversial when he made the painting. Bill Hartmann’s artwork has frequently graced the covers of the University of Arizona’s “Space Science Series” of topical books, often featuring impact themes. Earth-approaching asteroids are featured on the covers of Resources of Near-Earth Space and Hazards due to Comets and Asteroids. Bill’s cover for Asteroids II, published in 1989, shows a cratered body that looks remarkably like NEAR-Shoemaker’s first images of the asteroid Eros taken a decade later. The cover of Meteorites and the Early Solar System shows a dramatic, iconic image of two asteroids exploding as they collide. Bill Hartmann is one of the few scientists during the past half-century who have studied cratering from the broadest, most open-minded perspective, trying to elucidate the fundamental role it has played in shaping the surfaces of the planets and the properties of the smaller bodies in the solar system. Bill Hartmann’s vision of lunar and planetary cratering, and his career of research and public outreach on that topic, make him eminently qualified to receive the prestigious Barringer Medal.