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[1] In order to better understand the stability of water on Mars, and factors likely to affect that stability, we have measured the evaporation rate of water in a CO2 atmosphere at 7 mbar and ∼0°C in a large environmental chamber that minimizes fluctuation in conditions. The average evaporation rate we measured was 1.01 ± 0.19 mm/h. This includes correction for water vapor build-up in the chamber, but not the effect of Mars' lower gravity. When corrections for this are applied, our predicted evaporation rate for water on Mars at 0°C and 7 mbar is 0.73 ± 0.14 mm/h. This is in very good agreement with the value calculated by assuming that evaporation depends on diffusion and buoyancy. The consistency of these results suggests that – at least for these conditions – our approaches to the calculations and the laboratory simulations are reasonable.

[1] We have determined the evaporation rate of brine under simulated martian conditions at temperatures from 0°C to −26.0°C as part of our efforts to better understand the stability of water on Mars. Correcting for the effect of water build-up in the atmosphere and the lower gravity on Mars relative to Earth we observed a factor of almost 30 decrease in evaporation, from 0.88 mm/h at ∼0°C to 0.04 mm/h at −25.0°C. The results are in excellent agreement with the predictions of Ingersoll's (1970) theoretical treatment, lending support to the theory and our procedures. Thus brine formation will increase the stability of water on Mars not only by extending the liquid temperature range, but also by considerably decreasing the evaporation rate.

Chondrites are the largest group of meteorites. They can provide unique insights into the origins and early evolution of our Solar System, and even into the relationships between our Solar System and other stars in the vicinity of our Sun. The largest structural components of most chondrites are the glass-bearing chondrules, and there are numerous theories for their origin. This clear and systematic text summarizes the ideas surrounding the origin and history of chondrules and chondrites, drawing on research from the various scientific disciplines involved. With citations to a large number of published papers on the topic, it forms a comprehensive bibliography of the key research areas, and extensive illustrations provide a clear visual representation of the scientific theories. This text will be a valuable reference for graduate students and researchers in planetary science, geology, and astronomy.

Introduction The method to be used for mitigating the impact of an asteroid on Earth depends on the nature of the asteroid. A compact rock would react very differently to almost any violent mechanical event than would an object that consisted of unconsolidated dust and fragments. A water-rich, comet-like object would react very differently to laser heating than a completely hydrated object. Thus, impact mitigation begins with scientific investigation. We have been investigating physical processes likely to be occurring on asteroids in connection with our efforts to understand the origin and history of meteorites and their relationship to asteroids. In this connection, we have been developing proposals for a near-Earth asteroid sample return mission called Hera (Sears et al . 2002c) (Fig. 15.1). Hera will visit three near-Earth asteroids, spend 3 months to 1 year in reconnaissance, and then nudge itself gently down to the surface to collect three samples from each asteroid at geologically significant sites (Britt et al . 2001). By returning weakly consolidated surface samples, the Hera mission will clarify many issues relating to the asteroid–meteorite connection and the origin and evolution of the solar system (Sears et al . 2001). In addition, interstellar grains in the samples will shed light on the relationship between our Sun and other stars. The major challenge of the Hera mission is the design of the collector and this depends on a knowledge of the nature of the surface.

[1] Cathodoluminescence (CL) petrography provides a means of observing petrographic and compositional properties of geological samples not readily observable by other techniques. We report the low-magnification CL images of 60 sections of extraterrestrial materials. The images we report include ordinary chondrites (including type 3 ordinary chondrites and gas-rich regolith breccias), enstatite chondrites, CO chondrites and a CM chondrite, eucrites and a howardite, lunar highland regolith breccias, and lunar soils. The CL images show how primitive materials respond to parent body metamorphism, how the metamorphic history of EL chondrites differs from that of EH chondrites, how dark matrix and light clasts of regolith breccias relate to each other, how metamorphism affects eucrites, the texture of lunar regolith breccias and the distribution of crystallized lunar spherules (“lunar chondrules”), and how regolith working affects the mineral properties of lunar soils. More particularly, we argue that such images are a rich source of new information on the nature and history of these materials and that our efforts to date are a small fraction of what can be done.

In this paper we present the concept of a robotic instrument for in situ luminescence dating of near-surface sediments on Mars. The scientific objectives and advantages to be gained from the development of such an instrument are described, and the challenges presented by the Mars surface environment to the design and operation of the instrument are outlined.

[1] We report here experiments on NASA's KC-135 microgravity facility aimed at investigating metal-silicate fractionation in chondrites. Metal and sand particle mixtures, with sizes and relative proportions approximating chondritic values, were allowed to undergo density and aerodynamic sorting as air was passed through 310, ten-centimeter long 2.54 cm diameter columns under microgravity conditions. Metal and silicate fractionation was found to occur when gases passed through the mixtures and when the particle diameter ratio was large (∼3.0), with sand being enriched near the surface of the beds. This is contrary to experiments performed under terrestrial gravity and the semi-empirical Ergun equation. While the reason for this discrepancy is not well understood, the present results do suggest that separation of metal and silicates will readily occur under microgravity conditions on the surface of asteroids.

[1] In order to understand mechanical processes likely to be occurring on the surfaces of asteroids, we have performed experiments with mineral mixtures on NASA's KC-135 microgravity facility. The behavior of sand and iron filing mixtures, the sand and metal being in the proportions and with grain sizes of ordinary chondrite meteorites, was observed with digital cameras as gas was flowed upward through the mixtures and the plane went through cycles of positive, zero, negative and normal gravity. Partial separation of gas and sand occurred readily under gas flow and microgravity conditions and sometimes survived subsequent turbulence. This behavior is consistent with predictions of the Ergun equation derived from terrestrial experiments. The data have implications for understanding chondrite genesis, for understanding the spectra of asteroid surfaces, and for the design of equipment to function on asteroid surfaces.

[1] EL chondrites exhibit larger average metal grain sizes than EH chondrites, a difference attributed by Easton [1983] to metamorphic coarsening, as most EL chondrites are equilibrated, and most EH chondrites are unequilibrated. In this paper, we present metal grain size data for three unequilbrated EL3 chondrites (PCA 91020; ALH 85119; MAC 88180) , and three EH3 chondrites (ALH 84170; PCA 91085; PCA 91238). We find that EL3 chondrites have larger average metal grain sizes than EH3 chondrites, and that grain sizes of the unequilibrated enstatite chondrites are similar to those of equilibrated chondrites of the same class. We thus interpret the metal size distributions of enstatite chondrites as primarily reflecting their pre-metamorphic distributions. Shock processing appears to have had only minor influence on metal grain size distributions in these meteorites.

Between 2001 and 2004, Ursula Marvin published the oral histories of thirteen persons noted for their contributions to meteoritics and planetary science (Table 1). With her encouragement, and with the support of the editor of MAPS and NASA, I am continuing the series and the first article appears in this issue of MAPS. Oral histories have seen an increase in popularity in the last few decades. There are now several books on their objectives and execution. There was a time when historians shied away from them, believing them to be unreliable and lacking objectivity. Documents were what mattered. However, there is now a realization that despite their obvious drawbacks, they have a unique role to play in writing history. Several major scientific organizations have programs to obtain and archive oral histories, among them NASA (http://www.jsc.nasa.gov/ history/oral_histories/oral_histories.htm) and the American Institute of Physics (e.g., http://www.aip.org/history/ ohilist/4849.html). Never has the value of oral histories been more apparent than in documenting the history of the Apollo program, and there is hardly a serious book on the Apollo program that does not cite them. Of course, oral histories do not replace the documentary resources, the published and the unpublished papers cataloged in our libraries and museums. The oral histories complement the documentary histories. In a sense, the oral histories describe the sometimes subtle canvas on which the scientific advances were made. They identify the forces for change––intellectual, political, societal, and personal––that drove the scientific advances. This has always been true of science, and is true today. The Apollo program happened because World War II gave us the V2 and the Cold War, but writing on this canvas were the personalities of Von Braun, Jack Kennedy, James Webb, and many others. Writing on the canvas were also James Van Allen and Gerard Kuiper, so space and planetary science, as we now know this area of research, are also driven by space missions, politics, and national budgets. Does anyone doubt that remarkable evolution ofmeteorite research since the SecondWorldWarwas not duemainly to the space programand federal budgetary support? Reading the scientific publications and tracing the dendritic interconnections between published papers tells us what happened in the history of science, it does not tell us how and why. It is by understanding how all these forces interplay, intellectual, political, societal, and personal, that we write the history of science. What the oral histories are not are biographies, but to understand what drives a person we need to know their biography. What the oral histories are not are descriptions of publication lists, although we obviously need to understand the interviewee’s major contributions. What the oral histories are not is gossip, but we need to understand the small things that helped to set the scene and describe the personal dynamics that make us the scientists we are. Lastly, the oral histories are not an opportunity for self-promotion or short-cutting the peer review system in the publication of new work. This is not to say that the oral histories are not peer reviewed. They are, but they are reviewed as history, not science. There are a great many textbooks describing how an oral history should be prepared. There is even a history of oral history. Oral history papers are essentially a report of an interview. The interviewer should be prepared by reading the subject’s CV and publication list and reading or at least skimming some of the major publications. It is my practice to ask the interviewees to send me a list of their favorite twelve papers, to prepare them for the interview and provide some outline for discussing science progress. I am also including four or five figures that are intended to elaborate, clarify, or serve as a guide to the content of the interview. The textbooks say that the interviewer should be a historian and not a researcher in the field, and in this respect, I am

In his news focus article about meteoriticist John Wood and his views on the state of meteoritic science, Richard A. Kerr says, “The editor of the field's leading publication, Meteoritics and Planetary Science , had asked Wood to submit a manuscript, but the two of them could not agree on its format” (“A meteoriticist speaks out, his rocks remain mute,” 31 Aug., p. [1581][1]). The manuscript referred to was based on the Harold Masursky Lecture that Wood delivered at the 2000 Lunar and Planetary Science Conference. Wood's paper was sent to three reviewers, and the consensus was that the paper was not acceptable for publication in Meteoritics and Planetary Science. However, I was hopeful that with revision it might be publishable in the journal's supplement, which contains papers of value to the community but not necessarily appropriate for the journal. I requested changes accordingly, which were of substance, not format. The paper did not seem to me to be an assertion that chondrule research over the last four decades had been futile. Rather, it suggested that the avenues of interpretation pursued by this particular researcher had been fruitless. It was a valuable record of a frustrating career over a unique time in planetary science history, and I regret that it has not yet been made publishable. [1]: /lookup/doi/10.1126/science.293.5535.1581

Whether many of the 10,000 meteorites collected in the Antarctic are unlike those failing elsewhere is contentious. The Antarctic H chondrites, one of the major classes of stony meteorites, include a number of individuals with higher induced thermoluminescence peak temperatures than observed among non-Antarctic H chondrites. The proportion of such individuals decreases with the mean terrestrial age of the meteorites at the various ice fields. These H chondrites have cosmic-ray exposure ages of about 8 million years, experienced little cosmic-ray shielding, and suffered rapid postmetamorphic cooling. Breakup of the H chondrite parent body, 8 million years ago, may have produced two types of material with different size distributions and thermal histories. The smaller objects reached Earth more rapidly through more rapid orbital evolution.

Induced thermoluminescence studies provide a new and quantitative means of determining relative metamorphic intensities for eucrite meteorites, the simplest and most ancient products of basaltic volcanism. Using this technique, it is shown that the eucrites constitute a continuous metamorphic series and not, as commonly assumed, two groups of metamorphosed and nonmetamorphosed meteorites. It is suggested that the method may have applications to other basalts.

Comment and reply on the paper of K. Nishiizumi, D. Elmore et P.W. Kubik (1989) - Earth Planet. Sci. Lett. 93, 299-313

Comet simulation experiments are discussed, in the context of physical models and the results in cometary physics, gathered especially from the GIOTTO space mission to comet P’Halley. The “status of the today knowledge” about comets, the experiments could start from, is briefly reviewed. The setup of the KOSI (German = Kometen Simulation) — experiments and the techniques to produce cometary analogous material, on the basis of that knowledge are described in general, as for the different KOSI experiments. The limitations of the simulation of physical processes at the surface of real comets in an earth-bound laboratory are discussed, and the possibilities to receive common insights in cometary physics are shown. Methods and procedures are described, and the major results reviewed. As with attempting to reproduce any natural phenomenon in the laboratory, there are short-comings to these experiments, but there are possibly major new insights to be gained. Physical laws only have the same consequences under same experimental or environmental conditions. A number of small-scale comet simulation experiments have been performed, since the early 60ties in many laboratories, but the largest and most ambitious series of comet simulation experiments to date were performed between 1987 and 1993 using the German space agency’s (DLR) space hardware testing facilities in Cologne. These experiments were triggered by the scientific community after the comet P’Halley’s recurrence in 1986 and the many data gathered by the space missions in this year. Simulation experiments have proved valuable in developing methods for making cometary analogues, and for exploring specific properties of such materials in detail. These experiments provided new insights into the morphology and physical behavior of aggregates formed out of silicate- /water-ice -grains likely to exist in comets. The formation of a dust mantle on the surface, and a system of ice layers below the mantle from the different admixed materials, have been detected after the insolation of the artificial comet. The mechanisms for heat transfer between the comet’s surface and its interior, compositional, structural, and isotopic changes that occur near the comet’s surface, were described by modeling in accordance with the experimental results. The mechanisms of the ejection of dust and ice grains from the surface, and the importance of gas-drag in propelling grains were investigated by close-up video cameras.

— A new 2.8 kg meteorite find from the United States, Kansas University, is classified as an L6 (S3) chondrite based on optical microscopy and electron microprobe analysis of mafic minerals. Natural thermo-luminescence (TL) and 14C measurements suggest that the Kansas University meteorite has a short terrestrial age compared to other meteorite finds from this area and is not paired with the other local meteorite finds, Densmore (1879), Lawrence, Kansas and Long Island, Kansas.

In the U.K., Nestle's make a brand of breakfast cereal called Shreddies. It is a rather good cereal that I have eaten since being a child. This year we have the option of buying packets with a "REAL meteorite". Emblazoned all over the box are images of fire-trailing fireballs and the explanation "A meteor is a rock from space that has entered the Earth's atmosphere. The name changes to meteorite once it hits the surface".