Award of the 2024 Barringer Medal to Dr. John Spray

Dr. John Spray, founding director of the Planetary and Space Science Centre at the University of New Brunswick, Canada, has led a versatile and vigorous research team for over four decades. His contributions have ranged from field and laboratory studies of impact sites to ingenious explorations of basic material properties of solid bodies in the solar system. While obtaining degrees in mineral physics and earth sciences from Cardiff, Wales, and Cambridge, United Kingdom, John developed an interest in frictional melting in highly deformed rocks from Cyprus, the Scottish Highlands and elsewhere. Exceptionally, he supplemented field and laboratory investigations with experiments using equipment of his own design. With these, he subjected natural materials to extreme stresses and induced frictional melting, thereby emulating the formation of pseudotachylyte veins in rocks. At the same time, he added radiometric age determinations to his repertoire through collaborations with specialists in argon dating methods. Thus, he began a series of exceptionally diverse contributions to planetary science and space-oriented industries. Once in Canada, he was soon drawn to research in hypervelocity impact structures and meteoritics by focusing on the complex and economically important structure at Sudbury, Ontario. For over a decade, his Sudbury Project made major contributions to confirming its extraterrestrial origin by impact and its mid-Proterozoic age, and to drawing distinctions between pseudotachylyte-bearing breccias, intrusions of impact melt, and other features formed by extreme shock pressures. His project engaged students, colleagues, and collaborators from government and mining companies in over 50 person-years of research in analyzing Sudbury structure as a multi-ring impact basin. John broadened his studies of large impact structures by adding Manicouagan and Charlevoix in Quebec to his roster as well as aspects of Vredefort and Popigai. At Manicouagan, he took advantage of abundant drill cores produced by others in an unsuccessful search for Sudbury-type orebodies to refine understanding of its formation. An important though unanticipated result was the discovery that thick bodies of impact melt in the center of the structure had differentiated while crystallizing. This effectively resolved a long-standing debate about comparable igneous differentiation at Sudbury. Manicouagan also gave John and his colleagues structurally important impact breccia exposures, shock indicators such as stishovite and shatter cones in uplifted basement rocks, and details of the complex relationships between the impact structure and diverse country rocks. From these studies, he established Manicouagan's position as an important terrestrial impact structures providing a bridge between smaller craters and the largest on Earth, the Moon, and Mars. In expanding his terrestrial crater studies, John pursued the structural analysis of smaller craters such as Haughton in the Canadian arctic and elsewhere on the Shield. He also applied in-house uranium–helium and uranium–lead dating methods to more than a dozen impact structures for which suitable samples are available. A recent example is a stratigraphically convincing age for the Ordovician crater at Brent, Ontario, that had frustrated many earlier attempts. During this period, he reported on his extensive experimental investigations into frictional melting by collaborating in a special edition of Tectonophysics in 1992 followed in 2010 by a masterly review of the topic combining theory, experiment, and observation in Annual Review of Earth and Planetary Science. To these landmark summations, he later added an investigation into the mechanics of regolith formation on dry, airless planets by comparing the process of consolidating breccia into rocks with industrial sintering and impact welding. In establishing the Planetary and Space Science Centre at UNB in 2001, John consolidated his field and laboratory investigations of terrestrial craters and added studies of lunar, Martian, and meteorite samples. The Center houses drill core and related materials either on loan or long term and fostered an Earth Impact Database as part of its service to both the scientific community and the interested public. Most importantly, he expanded his experimental capabilities by acquiring a high-velocity impact research and technology facility to test both ultra-high and lower velocity impacts for aerospace and military applications as well as crater formation on planetary surfaces. His experiments included forming hypervelocity craters in anorthosite as an analogue for lunar highlands. Collaborations with similar facilities in France and Germany have deepened understanding of crater formation and ejecta production. In the case of Mars, his practical expertise assisted preparations for rover explorations. He has received awards from NASA and the European Space Agency for contributions to several missions and has led a team involved in the analysis of data obtained by Curiosity. Altogether John Spray's important and stimulating contributions have secured him a high place among planetary scientists. The Barringer Medal is fitting recognition of his thoughtful efforts to expand our understanding of impacts at all scales and stretch material science to the limits of practical experimentation. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

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