Oral Histories in Meteoritics and Planetary Science – XV: John Wood

Abstract– John Wood ( Fig. 1 ) was trained in Geology at Virginia Tech and M.I.T. To fulfill a minor subject requirement at M.I.T., he studied astronomy at Harvard, taking courses with Fred Whipple and others. Disappointed at how little was known in the 1950s about the origin of the earth, he seized an opportunity to study a set of thin sections of stony meteorites, on the understanding that these might shed light on the topic. This study became his Ph.D. thesis. He recognized that chondrites form a metamorphic sequence, and that idea proved surprisingly hard to sell. After brief service in the Army and a year at Cambridge University, John served for 3 years as a research associate with Ed Anders at the University of Chicago. He then returned to the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, where he spent the remainder of his career. At Chicago, he investigated the formation of the Widmanstätten structure, and found that the process informs us of the cooling rates of iron meteorites. Back in Cambridge, he collaborated with W. R. Van Schmus on a chondrite classification that incorporates metamorphic grade, and published on metal grains in chondrites, before becoming absorbed by preparations for the return of lunar samples by the Apollo astronauts. His group’s work on Apollo samples helped to establish the character of the lunar crust, and the need for a magma ocean to form it. Wood served as President of the Meteoritical Society in 1971–72 and received the Leonard Medal in 1978.

Figure 1 Open in figure viewer PowerPoint John Wood.     

Oral Histories in Meteoritics and Planetary Science—XIX: Klaus Keil

Abstract– Klaus Keil ( Fig. 1 ) grew up in Jena and became interested in meteorites as a student of Fritz Heide. His research for his Dr. rer. nat. became known to Hans Suess who––with some difficulty––arranged for him to move to La Jolla, via Mainz, 6 months before the borders of East Germany were closed. In La Jolla, Klaus became familiar with the electron microprobe, which has remained a central tool in his research and, with Kurt Fredriksson, he confirmed the existence of Urey and Craig’s chemical H and L chondrite groups, and added a third group, the LL chondrites. Klaus then moved to NASA Ames where he established a microprobe laboratory, published his definitive paper on enstatite chondrites, and led in the development of the Si(Li) detector and the EDS method of analysis. After 5 years at Ames, Klaus became director of the Institute of Meteoritics at the University of New Mexico where he built up one of the leading meteorite research groups while working on a wide variety of projects, including chondrite groups, chondrules, differentiated meteorites, lunar samples, and Hawai’ian basalts. The basalt studies led to a love of Hawai’i and a move to the University of Hawai’i in 1990, where he has continued a wide variety of meteorite projects, notably the role of volcanism on asteroids. Klaus Keil has received honorary doctorates from Friedrich‐Schiller University, Jena, and the University of New Mexico, Albuquerque. He was President of the Meteoritical Society in 1969–1970 and was awarded the Leonard Medal in 1988.

Figure 1 Open in figure viewer PowerPoint Klaus Keil at the University of Hawai’i at Manoa, 2007.     

Oral histories in meteoritics and planetary science—XVI: Donald D. Bogard

Abstract– Donald D. Bogard (Don, Fig. 1 ) became interested in meteorites after seeing the Fayetteville meteorite in an undergraduate astronomy class at the University of Arkansas. During his graduate studies with Paul Kuroda at Arkansas, Don helped discover the Xe decay products of ²⁴⁴Pu. After a postdoctoral period at Caltech, where he learned much from Jerry Wasserburg, Peter Eberhardt, Don Burnett, and Sam Epstein, Don became one of a number of young Ph.D. scientists hired by NASA’s Manned Spacecraft Center to set up the Lunar Receiving Laboratory (LRL) and to perform a preliminary examination of Apollo samples. In collaboration with Oliver Schaeffer (SUNY), Joseph Zähringer (Max Planck, Heidelberg), and Raymond Davis (Brookhaven National Laboratory), he built a gas analysis laboratory at JSC, and the noble gas portion of this laboratory remained operational until he retired in 2010. At NASA, Don worked on the lunar regolith, performed pioneering work on cosmic ray produced noble gas isotopes and Ar‐Ar dating, the latter for important insights into the thermal and shock history of meteorites and lunar samples. During this work, he discovered that the trapped gases in SNC meteorites were very similar to those of the Martian atmosphere and thus established their Martian origin. Among Don’s many administrative accomplishments are helping to establish the Antarctic meteorite and cosmic dust processing programs at JSC and serving as a NASA‐HQ discipline scientist, where he advanced peer review and helped create new programs. Don is a recipient of NASA’s Scientific Achievement and Exceptional Service Medals and the Meteoritical Society’s Leonard Medal.

Figure 1 Open in figure viewer PowerPoint Donald Bogard.     

Oral histories in meteoritics and planetary science – XXII: John T. Wasson

In this interview, John Wasson (Fig.  1 ) describes his childhood and undergraduate years in Arkansas and his desire to pursue nuclear chemistry as a graduate student at MIT. Upon graduation, John spent time in Munich (Technische Hochschule), the Air Force Labs in Cambridge, MA, and a sabbatical at the University of Bern where he developed his interests in meteorites. Upon obtaining his faculty position at UCLA, John established a neutron activation laboratory and began a long series of projects on the bulk compositions of iron meteorites and chondrites. He developed the chemical classification scheme for iron meteorites, gathered a huge set of iron meteorite compositional data with resultant insights into their formation, and documented the refractory and moderately volatile element trends that characterize the chondrites and chondrules. He also spent several years studying field relations and compositions of layered tektites from Southeast Asia, proposing an origin by radiant heating from a mega‐Tunguska explosion. Recently, John has explored oxygen isotope patterns in meteorites and their constituents believing the oxygen isotope results to be some of the most important discoveries in cosmochemistry. John also describes the role of postdoctoral colleagues and their important work, his efforts in the reorganization and modernization of the Meteoritical Society, his contributions in reshaping the journal Meteoritics, and how, with UCLA colleagues, he organized two meetings of the society. John Wasson earned the Leonard Medal of the Meteoritical Society in 1992 and the J. Lawrence Smith Medal of the National Academy in 2003.

Figure 1 Open in figure viewer PowerPoint John T. Wasson.

DS

John, thank you for letting me document your oral history. Let us start with my normal opening question, how did you get interested in meteorites?

JW

My Ph.D. research was in nuclear chemistry at MIT. Until late in my studies I thought I could be a nuclear chemist using the classical scientific method. That is, you gather data on a topic that seems interesting, you look for patterns in the data, and you write an interpretative paper that explains the data. I had learned, though, by going to Gordon Conferences, that this was not the way nuclear chemistry was being done. Nuclear chemists measured gamma ray energies as accurately as they could, they tried to fit these into energy levels diagrams, and then the nuclear physicists took over and interpreted the data. The nuclear physicists looked for the patterns in the energy‐level diagrams and made the models. That was not what I had in mind. But while I was at MIT, I heard lectures by Harold Urey, Hans Suess, and James Arnold. These were people whose backgrounds were not that different from mine and all three extolled the virtues of working on meteorites, and how you could learn neat things about how the solar system worked. That's a strength of MIT, exposure to neat ideas, and I credit the institution for doing this. So that was it. I was hooked.

DS

You have talked to us about how you became interested in meteorites, let's go back and talk about your precollege years.

     

Determination of the cooling rates and nucleation histories of eight group IVA iron meteorites using local bulk Ni and P variation

Cooling rates and nucleation histories of six low-Ni and two high-Ni members of group IVA iron meteorites were calculated by a mid-taenite concentration-taenite lamella width method that included the effects of local bulk Ni and P variation. The local bulk Ni is determined experimentally as described in K. L. Rasmussen [Icarus45, 564–576 (1981)]. The local bulk P parameter, included for the first time in the present work, is estimated from the phase diagram during the simulation. Two parent bodies are suggested for group IVA. The body containing the high-Ni members had a cooling rate (～2°K/My) lower than earlier cooling rate determinations on IVA members. The variable (by a factor of 4) cooling rates found for the low-Ni members imply a raisin origin. The nucleation histories of the meteorites are interpreted as reflecting the very early shock histories of the meteorite parent bodies.     

The cooling rates of iron meteorites—A new approach

Measurements of Ni concentration profiles of a large number of neighboring kamacite and taenite lamellae in the iron meteorite Cape York (IIIA) have revealed that the kamacite plates have nucleated in a taenite of varying Ni concentration, equal to or above the bulk Ni concentration of the meteorite. This variation indicates that the kamacite plates nucleated stepwise (i.e., independently) during cooling through a certain temperature interval, rather than simultaneously after more or less undercooling of the meteorite. The latter is assumed in most previous cooling rate determinations (e.g., Moren and Goldstein, 1978). In this paper the measured local bulk Ni concentrations are used in the computer simulation of the evolution of the Widmannstaetten pattern in order to calculate the cooling rate of the meteorite. The cooling rate obtained for Cape York is 1.3°K/my. In most previous work, a correlation is seen between the resulting taenite width and the cooling rate in one and the same meteorite. No such correlation is seen using the present method.     

Oral Histories in Meteoritics and Planetary Science––XVI: Grenville Turner

Abstract– In this interview, Grenville Turner ( Fig. 1 ) recounts how he became interested in meteorites during postdoctoral research with John Reynolds at the University of California, Berkeley, after completing a DPhil with Ken Mayne at the University of Oxford. At Berkeley, he worked on xenon isotopes with fellow students Bob Pepin and Craig Merrihue, but Reynolds’ insistence that they analyze all the inert gases in their samples meant that they also made important contributions to Ne isotope studies and potassium‐argon dating leading to the Ar‐Ar technique. In 1964, Grenville obtained a teaching position at the University of Sheffield where he developed his own laboratory for inert gas isotope measurements. After the return of samples from the Moon by the Apollo program, he became involved in determining the chronology of volcanism and major impacts on the Moon. In 1988, Grenville and his team moved to the University of Manchester as part of a national reorganization of earth science departments. During the post Apollo years, Grenville’s interest turned to the development of new instrumentation (resonance ionization mass spectrometry and the ion microprobe), and to problems in terrestrial isotope geochemistry, particularly the source of inert gases in fluid inclusions. He received the Leonard Medal of the Meteoritical Society in 1999, and he has also received awards from the Royal Society, the European Association of Geochemistry, and the Royal Astronomical Society.

Figure 1 Open in figure viewer PowerPoint Grenville Turner.     

The metallographic cooling rate method revised: Application to iron meteorites and mesosiderites

Abstract— A major revision of the current Saikumar and Goldstein (1988) cooling rate computer model for kamacite growth is presented. This revision incorporates a better fit to the α/α + γ phase boundary and to the γ/α + γ phase boundary particularly below the monotectoid temperature of 400 °C. A reevaluation of the latest diffusivities for the Fe‐Ni system as a function of Ni and P content and temperature is made, particularly for kamacite diffusivity below the paramagnetic to ferromagnetic transition. The revised simulation model is applied to several iron meteorites and several mesosiderites. For the mesosiderites we obtain a cooling rate of 0.2 °C/Ma, about 10x higher than the most recent measured cooling rates. The cooling rate curves from the current model do not accurately predict the central nickel content of taenite halfwidths smaller than ～10 μm. This result calls into question the use of conventional kamacite growth models to explain the microstructure of the mesosiderites. Kamacite regions in mesosiderites may have formed by the same process as decomposed duplex plessite in iron meteorites.     

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—XXIV: William K. Hartmann

In this interview, William Hartmann (Bill, Fig.  1 ) describes how he was inspired as a teenager by a map of the Moon in an encyclopedia and by the paintings by Chesley Bonestell. Through the amateur journal “Strolling Astronomer,” he shared his interests with other teenagers who became lifelong colleagues. At college, he participated in Project Moonwatch, observing early artificial satellites. In graduate school, under Gerard Kuiper, Bill discovered Mare Orientale and other large concentric lunar basin structures. In the 1960s and 1970s, he used crater densities to study surface ages and erosive/depositional effects, predicted the approximately 3.6 Gyr ages of the lunar maria before the Apollo samples, discovered the intense pre‐mare lunar bombardment, deduced the youthful Martian volcanism as part of the Mariner 9 team, and proposed (with Don Davis) the giant impact model for lunar origin. In 1972, he helped found (what is now) the Planetary Science Institute. From the late 1970s to early 1990s, Bill worked mostly with Dale Cruikshank and Dave Tholen at Mauna Kea Observatory, helping to break down the Victorian paradigm that separated comets and asteroids, and determining the approximately 4% albedo of comet nuclei. Most recently, Bill has worked with the imaging teams for several additional Mars missions. He has written three college textbooks and, since the 1970s, after painting illustrations for his textbooks, has devoted part of his time to painting, having had several exhibitions. He has also published two novels. Bill Hartmann won the 2010 Barringer Award for impact studies and the first Carl Sagan Award for outreach in 1997.

Figure 1 Open in figure viewer PowerPoint William K. Hartmann taken 2010 Aug 2 (Photo: Gayle Hartmann).

DS

Bill thank you very much for doing this. I would like to start with a very general question. What is the one incident in your life above all others that has determined the nature of your career?

WKH

I would say that what initially stirred my excitement for this topic were the books I stumbled across as a teenager. One event I recall was that my brother, who was 8 years older than I was, had a young person's encyclopedia called the Book of Knowledge. One day I was looking at that book and there was this map of the Moon. Craters, mountains, plains, all sorts of features. That blew me away. The concept that there was this other land, not just a shining thing in the sky, but a geological body, a new geographical place. There was also a book by Willy Ley and Chesley Bonestell, Conquest of Space, which had all these marvelous paintings by Bonestell, visualizing what it was like on other planets. It came out in 1949. I am fond of my copy of that book because my father somehow managed to get Willy Ley, a German expatriate colleague of von Braun's, a writer and popularizer for space, to come to our town and give a talk and autograph my book. Many years later I met Chesley Bonestell and got him to autograph the book. There are not very many copies of that book with the signatures of both authors! The paintings gave me a real desire to want to know what it would be like on other worlds.

     

On time variations of the intensity of galactic cosmic rays for the recent billion years from the data on exposure ages of iron meteorites

To ascertain probable variations of the intensity of galactic cosmic rays (GCR) for the recent billion years, the distribution of exposure ages T of iron meteorites has been analyzed. We considered all ~80 values of ages from the data by Voshage and Feldmann (1979), Voshage et al. (1983), and Voshage (1984), as well as a set of values obtained from the correction for eliminating the meteorites formed in a single collision. To correct the data, the Akaike information criterion was used. For the distributions of the phase values Ph = T/t–int(T/t), the dependence of the criterion χ ² on the presumable period t in the exposure age variations was analyzed. For t ~ 400–500 Myr and, partly, for t ~ 150 Myr, the significant deviations of this criterion from the corresponding mean values were found. To clear up the influence of the GCR intensity variations on the age distribution, the numerical models were calculated with an account of the set of ages randomly distributed in the interval of 0–1000 Myr with the presumptive mean lifetime of iron meteorites in outer space τ = 700 Myr. It has been ascertained that, for variations with a period of t = 450 Myr, the distribution of exposure ages of the model set is similar to that found for iron meteorites. The obtained data suggest that the GCR intensity variations with a period of approximately 400–500 Myr have probably existed during the recent billion years. These variations may be caused by periodic passages of the Solar System through spiral arms of the Galaxy. It has been shown that the earlier discussed changes in the GCR intensity with a period of ~150 Myr (Shaviv, 2002; 2003; Scherer et al., 2006) are less defined.     

A model of possible variations of the galactic cosmic ray intensity over the recent billion years

Based on the analysis of published data on exposure ages of iron meteorites determined with the ⁴⁰K/K method (T _K) and ages calculated using short-lived cosmogenic radionuclides (with the half-life T _1/2 < 1 Myr) in combination with stable cosmogenic isotopes of noble gases (T_RS), the following results have been obtained. (1) The distribution of T _RS ages (106 values) has an exponential shape, similar to that for ordinary chondrites, but different from the distribution of T _K ages (80 values). The difference is most likely due to small amounts of data for meteorites with low T _K ages (less than ~200–300 Myr). The latter can be ascribed to the difficulty of measurement of small concentrations of cosmogenic potassium isotopes. This circumstance makes the selection of meteorites with ⁴⁰K/K ages nonrepresentative and casts doubt on the correctness of conclusions about the variations of the intensity of galactic cosmic rays (GCR) based on the analysis of distribution of these ages. (2) The magnitude of the known effect (systematic overestimation of T _K ages in comparison with T _RS ages) has been refined. The value k = T _K/T _RS = 1.51 ± 0.03 is acquired for the whole population of data. We have shown the inefficiency of the explanation of this effect on account of an exponential change in the GCR intensity (I _T ) with time (T) according to the relation I _T = I ₀exp(–γT) over the whole range of ages of iron meteorites. (3) In order to explain the overestimation of T _K ages in comparison with T _RS ages, a model has been proposed, according to which the GCR intensity has exponentially increased in the interval of 0–1500 Myr governed by the relation: I _T = I _{T = 1500} (1 + αexp(–βT)). For one of the variants of this model, the GCR intensity has exponentially increased by a factor of two only over the recent ~300 Myr, remaining approximately constant for the rest of the time. The data acquired with the use of this model indicate that the measured T _K ages are close to the actual time that the meteorites existed in space; the data are in agreement with the observed exponential distribution of T _RS ages.     

Silicon in iron meteorite metal

Abstract– We report Si concentrations in the metal phases of iron meteorites. Analyses were performed by secondary ion mass spectrometry using a CAMECA 1270 ion probe. The Si concentrations are low (0.09–0.46 μg g^?1), with no apparent difference in concentration between magmatic and nonmagmatic iron meteorites. Coexisting kamacite and Ni‐rich metal phases have similar Si contents. Thermodynamic calculations show that Fe,Ni‐metal in equilibrium with silicate melts at temperatures where metal crystallizes should contain approximately 100 times more Si than found in iron meteorites in this work. The missing Si may either occur as tiny silicate inclusions in metal or it may have diffused as Si‐metal into surrounding silicates at low temperatures. In both cases, extensive low‐temperature diffusion of Si in metal is required. It is therefore concluded that low Si in iron meteorites is a result of subsolidus reactions during slow cooling.     

The structure and composition of metal particles in two type 6 ordinary chondrites

Abstract— The purpose of this study is to examine, using light optical and electron optical techniques, the microstructure and composition of metal particles in ordinary chondritic meteorites. This examination will lead to the understanding of the low temperature thermal history of metal particles in their host chondrites. Two type 6 falls were chosen for study: Kernouvé (H6) and Saint Severin (LL6). In both meteorites, the taenite particles consisted of a narrow rim of high Ni taenite and a central region of cloudy zone similar to the phases observed in iron meteorites. The cloudy zone microstructure was coarser in Saint Severin than in Kernouvé due to the higher bulk Ni content of the taenite and the slower cooling rate, 3 K Ma^?1 vs. 17 K Ma^?1. Three microstructural zones were observed within the high Ni taenite region in both meteorites. The origin of the multiple zones is unknown but is most likely due to the high Ni taenite cooling into the two phase γ″ (FeNi) + γ′ (FeNi₃) region of the low temperature Fe-Ni phase diagram. Another explanation may be the presence of uniform size antiphase boundaries within the high Ni taenite. Finally, abnormally wide high Ni taenite regions are observed bordering troilite. The wide zones are probably caused by the diffusion of Ni from troilite into the high Ni taenite borders at low cooling temperatures.     

Stuart H. Perry's contributions to meteorite collection and research, 1927–1957

Abstract— Stuart H. Perry (1874–1957), an influential Michigan newspaper editor and publisher and a vice president of the Associated Press, developed a passionate interest in collecting and studying meteorites in the 1920s and 1930s. Firmly believing that meteorites belong in great museums where they can be properly investigated, he generously donated his meteorites to various museums after he finished his own study of them. He had a sincere interest in the National Collection of Meteorites, and donated 192 specimens–‐mostly irons–‐to the U.S. National Museum; these constituted some of the most important meteorites in its collection, and moved iron meteorites to center stage, a position still occupied. By applying current metallographic methods to the study of iron meteorites, Perry directed scientists to a powerful new research tool, which led to major advances in our understanding of meteoritic irons and helped give rise to a new field within planetary sciences. His groundbreaking monograph The metallography of meteoric iron served as a standard reference collection of metallographic photomicrographs of iron meteorites for more than 30 years. It remained an insightful and useful work on the structure of meteoritic iron until improved binary and ternary phase diagrams in the Fe‐Ni(‐P) system allowed a more detailed treatment of the formation of iron meteorites. Perry received many honors for his work, and held office in the Meteoritical Society, serving as a councilor from 1941–1950, and as a vice president from 1950–1957.     

The formation of the Widmanstätten structure in meteorites

Abstract— We have evaluated various mechanisms proposed for the formation of the Widmanstätten pattern in iron meteorites and propose a new mechanism for low P meteoritic metal. These mechanisms can also be used to explain how the metallic microstructures developed in chondrites and stony‐iron meteorites. The Widmanstätten pattern in high P iron meteorites forms when meteorites enter the three‐phase field α + γ + Ph via cooling from the γ + Ph field. The Widmanstätten pattern in low P iron meteorites forms either at a temperature below the (α + γ)/(α + γ + Ph) boundary or by the decomposition of martensite below the martensite start temperature. The reaction γ → α + γ, which is normally assumed to control the formation of the Widmanstätten pattern, is not applicable to the metal in meteorites. The formation of the Widmanstätten pattern in the vast majority of low P iron meteorites (which belong to chemical groups IAB‐IIICD, IIIAB, and IVA) is controlled by mechanisms involving the formation of martensite α₂. We propose that the Widmanstätten structure in these meteorites forms by the reaction γ → α₂ + γ → α + γ, in which α₂ decomposes to the equilibrium α and γ phases during the cooling process. To determine the cooling rate of an individual iron meteorite, the appropriate formation mechanism for the Widmanstätten pattern must first be established. Depending on the Ni and P content of the meteorite, the kamacite nucleation temperature can be determined from either the (γ + Ph)/(α + γ + Ph) boundary, the (α + γ)/(α + γ + Ph) boundary, or the M_s temperature. With the introduction of these three mechanisms and the specific phase boundaries and the temperatures where transformations occur, it is no longer necessary to invoke arbitrary amounts of under‐cooling in the calculation of the cooling rate. We conclude that martensite decomposition via the reactions γ → α₂ → α + γ and γ → α₂ + γ → α + γ are responsible for the formation of plessite in irons and the metal phases of mesosiderites, chondrites, and pallasites. The hexahedrites (low P members of chemical group IIAB) formed by the massive transformation through the reaction γ → α_m → α at relatively high temperature in the two‐phase α + γ region of the Fe‐Ni‐P phase diagram near the α/(α + γ) phase boundary.     

THE COMPOSITION OF IRON METEORITES: A STUDY BY FACTOR ANALYSIS

A factor analysis has been performed on nickel and trace element data for iron meteorites. The technique shows that the present distribution of these elements is the result of three processes. These can be identified from the elements involved:

• 1 Ga, Ge, Sb and Zn (condensation and accretion).
• 2 Ni, Pd, Co and Cu (oxidation and sulphuration).
• 3 Ir, Au, As, Re, Pt, Os, Ru and Cr (an igneous event).

The distribution of Mo, however, is not readily explicable in terms of these processes. Within the groups IAB and IIAB only one process is required for all elements, but in groups IIIAB and IVA the situation for Ga, Ge and Sb is more complex.     

Mass‐dependent fractionation of nickel isotopes in meteoritic metal

Abstract— We measured nickel isotopes via multicollector inductively coupled plasma mass spectrometry (MC‐ICPMS) in the bulk metal from 36 meteorites, including chondrites, pallasites, and irons (magmatic and non‐magmatic). The Ni isotopes in these meteorites are mass fractionated; the fractionation spans an overall range of ～0.4‰ amu^?1. The ranges of Ni isotopic compositions (relative to the SRM 986 Ni isotopic standard) in metal from iron meteorites (～0.0 to ～0.3‰ amu^?1) and chondrites (～0.0 to ～0.2‰ amu^?1) are similar, whereas the range in pallasite metal (～–0.1 to 0.0‰ amu^?1) appears distinct. The fractionation of Ni isotopes within a suite of fourteen IIIAB irons (～0.0 to ～0.3‰ amu^?1) spans the entire range measured in all magmatic irons. However, the degree of Ni isotopic fractionation in these samples does not correlate with their Ni content, suggesting that core crystallization did not fractionate Ni isotopes in a systematic way. We also measured the Ni and Fe isotopes in adjacent kamacite and taenite from the Toluca IAB iron meteorite. Nickel isotopes show clearly resolvable fractionation between these two phases; kamacite is heavier relative to taenite by ～0.4‰ amu^?1. In contrast, the Fe isotopes do not show a resolvable fractionation between kamacite and taenite. The observed isotopic compositions of kamacite and taenite can be understood in terms of kinetic fractionation due to diffusion of Ni during cooling of the Fe‐Ni alloy and the development of the Widmanstätten pattern.     

Frederick C. Leonard: A history and personal recollections

As a child Frederick C. Leonard displayed such a precocious aptitude for astronomy that he became known as “Chicago's Boy Astronomer.” But within a decade after receiving his Ph.D., his interests had turned to meteorites. He persuaded Harvey Nininger to help him found the Society for Research on Meteorites, later renamed The Meteoritical Society, in 1933—a time when the study of meteorites was not considered a worthy pursuit of serious scientists. He nurtured the Society and held it together through the Great Depression, World War II, a destructive feud, and a significant personal and family crisis. He obtained legitimacy and affiliation for the Society with mainstream scientific organizations. He was its first President, and he was Editor of its publications from the Society's founding until a year before his death in 1960. Through it all he was a persistent advocate for the importance of the study of meteorites and the legitimacy of meteoritics as a valuable field of science.