Oral Histories in Meteoritics and Planetary Science – XX: Dale Cruikshank

Abstract– In this interview, Dale Cruikshank ( Fig. 1 ) explains how as an undergraduate at Iowa State University he was a summer student at Yerkes Observatory where he assisted Gerard Kuiper in work on his Photographic Lunar Atlas. Upon completing his degree, Dale went to graduate school at the University of Arizona with Kuiper where he worked on the IR spectroscopy of the lunar surface. After an eventful 1968 trip to Moscow via Prague, during which the Soviets invaded Czechoslovakia, Dale assumed a postdoc position with Vasili Moroz at the Sternberg Astronomical Institute and more observational IR astronomy. Upon returning to the United States and after a year at Arizona, Dale assumed a position at the University of Hawai’i that he held for 17 years. During this period Dale worked with others on thermal infrared determinations of the albedos of small bodies beyond the asteroid Main Belt, leading to the recognition that low‐albedo material is prevalent in the outer solar system that made the first report of complex organic solids on a planetary body (Saturn’s satellite Iapetus). After moving to Ames Research Center, where he works currently, he continued this work and became involved in many outer solar system missions. Dale has served the community through his involvement in developing national policies for science‐driven planetary exploration, being chair of the DPS 1990–1991 and secretary/treasurer for 1982–1985. He served as president of Commission 16 (Physics of Planets) of the IAU (2001–2003). He received the Kuiper prize in 2006.

Figure 1 Open in figure viewer PowerPoint Dale P. Cruikshank.     

Oral Histories in Meteoritics and Planetary Science—XXIII: Dieter Stöffler

In this interview, Dieter Stöffler (Fig. 1) describes how his interest in meteorites and impact craters dates from his Ph.D. studies at the University of Tübingen when it was learned that the Ries crater was formed by impact. A paper by Dieter's advisor, Wolf von Engelhardt, also triggered an interest in meteorites. After graduation, Dieter helped to establish a laboratory for high pressure mineralogy and he examined rocks from the Ries crater, which led to the concept of progressive shock metamorphism. The group also worked on newly returned Apollo samples and guided astronauts over the crater. A year at the NASA Ames Research Center taught Dieter about experimental impact research with a light‐gas gun. After a few more years at Tübingen, Dieter obtained a professorship at the University of Münster where he created the Institute of Planetology, got involved in planning space missions including comet sample return, and continued high pressure mineralogy in collaboration with colleagues in Freiburg. Through several decades of research, Dieter and colleagues have documented the effects of shock on all the major rock‐forming minerals and devised widely accepted schemes for the classification of shocked rocks. After the unification of Germany, Dieter became Director of the Natural History Museum in Berlin, during which he made much progress rebuilding the laboratories and the collections. Dieter also helped to create a museum and research center in the Ries crater. He received the Barringer Award of the Meteoritical Society in 1994 and several prestigious awards in Germany.     

The non‐trivial problem of meteorite pairing

Abstract— Pairing is the procedure of identifying fragments of a single meteorite fall (that were separated during atmospheric passage or during terrestrial history) by establishing the similarity of two or more meteorite fragments. We argue that pairing is governed by two principles, that only a single mismatch of properties is required to refute a proposed pairing, and that virtually all pairings bear some degree of uncertainty. Using data distributions for modern falls, we take a probability approach to estimate degrees of certainty associated with proposed pairings, emphasizing the importance of unusual features. For new pairing criteria or new analytical additions to old criteria, the degree of variation within individual meteorites must be delineated and the degree of variation within meteorite classes must be quantified. Criteria for pairing can be divided into (1) parent body history indicators, (2) meteoroid space history indicators, and (3) terrestrial history indicators. Included in these categories are 11 specific criteria, including petrographic textures, mineralogy and mineral composition, terrestrial age estimates, cosmic‐ray exposure ages, and natural thermoluminescence (TL) levels. Not all criteria are applicable to all meteorite types. About 2275 pairings suggested in the literature have been subjected to this analysis. Many literature pairings, especially those involving common meteorite types, bear large uncertainties due to lack of data.     

The formation of asteroid satellites in large impacts: results from numerical simulations

We present results of 161 numerical simulations of impacts into 100-km diameter asteroids, examining debris trajectories to search for the formation of bound satellite systems. Our simulations utilize a 3-dimensional smooth-particle hydrodynamics (SPH) code to model the impact between the colliding asteroids. The outcomes of the SPH models are handed off as the initial conditions for N-body simulations, which follow the trajectories of the ejecta fragments to search for the formation of satellite systems. Our results show that catastrophic and large-scale cratering collisions create numerous fragments whose trajectories can be changed by particle-particle interactions and by the reaccretion of material onto the remaining target body. Some impact debris can enter into orbit around the remaining target body, which is a gravitationally reaccreted rubble pile, to form a SMAshed Target Satellite (SMATS). Numerous smaller fragments escaping the largest remnant may have similar trajectories such that many become bound to one another, forming Escaping Ejecta Binaries (EEBs). Our simulations so far seem to be able to produce satellite systems qualitatively similar to observed systems in the main asteroid belt. We find that impacts of 34-km diameter projectiles striking at 3 km s⁻¹ at impact angles of ∼30° appear to be particularly efficient at producing relatively large satellites around the largest remnant as well as large numbers of modest-size binaries among their escaping ejecta.     

Carolina Thunder Revisited: Toward a Transcultural View of Winston Cup Racing*

Almost three decades ago, cultural geographer Richard Pillsbury documented the national expansion of NASCAR and what he considered the erosion of major‐league stock car racing as a unique southern tradition. This claim is reassessed in light of recent research, leading us to suggest that the sport is actually “transcultural” in nature. It is influenced simultaneously by tradition and transition, as well as regional and national forces. In revisiting Pillsbury's seminal work, we document major changes and continuities in Winston Cup racing and briefly examine two North Carolina cases that provide contradictory views on the current relationship between the sport and the American South. North Wilkesboro illustrates how the changing geography of track locations can devalue and demoralize places associated with the tradition of southern stock car racing. The greater Charlotte area demonstrates that the South remains an important part of NASCAR, serving as a gathering place and “knowledge community” for drivers, racing teams, and fans from across the country. In addition to advancing research in the geography of sport and popular culture, the article encourages readers to think critically about regional cultures and their relationship to the forces of nationalization.     

Short-Timescale Chemo-Mechanical Effects and their Influence on the Transport Properties of Fractured Rock

Anomalous changes in permeability are reported in fractures circulated by fluids undersaturated with respect to the mineral host. Under net dissolution and net removal of mineral mass, fractures may alternately gape or seal, depending on the prevailing mechanical and chemical conditions. The influence on transport properties is observed to be large, rapid, and irreversible: Permeabilities may change by two orders of magnitude in a month, and the direction of permeability change may switch spontaneously, for no apparent change in environmental forcing. These behaviors are apparent in continuous circulation experiments conducted on fractures in novaculite and limestone, intermittently imaged by X-ray CT. In novaculite, permeability reduces by two orders of magnitude as silica is net removed from the sample. Surprisingly, these changes can occur at modest temperatures (~80°C) and stresses (~3.5 MPa), where compaction progresses as temperatures are incremented. Isothermal (~20°C) circulation tests in limestone show similar compaction driven by pressure solution. Where circulation remains undersaturated in Ca, the change in permeability spontaneously switches from net reduction to net increase as a wormhole forms. The surprising magnitude and rapidity of these changes are investigated in the context of the competition between stress- and chemistry-mediated effects.     

A Street Fit for a King: Naming Places and Commemoration in the American South

The naming of streets after Martin Luther King, Jr. (MLK) is an importantarena for African Americans as they rewrite the landscape of southern identity and commemoration. While less ornate and ostentatious than museums and monuments, MLK streets are powerful and highly contested cultural geographies because of their potential to connect disparate communities and incorporate a vision of the past into the spatial practices of everyday life. They reveal the importance of location, particularly intra‐urban location, to public memorialization. Naming streets for King is a significant part of the nonmetropolitan South as well as larger cities and dependent upon the relative size of a city's African‐American population. When estimating the intra‐urban character of MLK streets within several southern states, findings suggest that they are located in census areas that are generally poorer and with more African Americans than citywide averages. Analysis reveals a geographic unevenness in the frequency of businesses having an address identified with King. When compared with the stereotypical American thoroughfare of “Main” Street, the address composition of MLK streets appears to be more residential in nature, although there is significant state by state variation.     

Probing the magnetic field around protostars

We present recent JCMT polarimetric observations of the Oph A cloud core and the S106 HII region. We infer the magnetic field structure in these regions.