Citation for Dr. Conel M. O'D. Alexander, Leonard Medalist, 2025

Abstract

President Consolmagno, friends and colleagues of the Meteoritical Society, it gives me great pleasure to present Dr. Conel Michael O'Donel Alexander (Figure 1) of the Carnegie Institution of Washington as the 2025 recipient of the Leonard Medal. Conel is honored for the fundamental and important contributions he has made to many aspects of meteoritics and allied fields, including the nature and origin of chondrite matrix, the origin of presolar grains, the nature and origin of water and organic matter in the Solar System, the origin of chondrules, and the origin of major cosmochemical trends across the Solar System. He has made these contributions using a vast array of analytical and modeling tools. I first met Conel in July 1991, on my first day of graduate school at Washington University in St. Louis, where Conel was a postdoc. He became an important mentor and eventually my longest-running and closest scientific collaborator and a dear friend. I therefore feel very privileged to provide this citation.

Conel's grandfather Hugh Alexander was a famous cryptologist who helped crack the Enigma code in World War II and a famous chess grandmaster. His father Michael Alexander was an Olympic medalist in fencing and an important British diplomat, among other things serving as diplomatic personal secretary to Prime Minister Margaret Thatcher. Conel inherited the formidable intellect of his parents and grandparents and we are fortunate he chose to apply it to investigating meteorites and the mysteries they hold. He earned a bachelor's degree in Geology from Imperial College in 1983 and his PhD in Experimental Physics from the University of Essex in 1987. For his doctoral work, he worked with Professor David Barber and with Dr Robert Hutchison (Natural History Museum, London), applying transmission electron microscopy to the matrix of ordinary chondrites. Application of TEM to meteorites was still relatively rare, and Conel made the ground-breaking discovery that the least altered ordinary chondrites contained clay minerals in their matrix, belying the belief at the time that OCs were bone dry. As Prof. Monica Grady stated in her nominating letter, this “discovery was the starting point of a career that has embraced a range of disciplines and techniques applied to a range of objects (meteorites, micrometeorites, Earth, Moon, Mars, asteroids, comets) in order to understand the range of processes that ultimately resulted in the Solar System.”

Presolar grains were discovered in carbonaceous chondrites in 1987 and immediately piqued Conel's interest. Upon receiving his PhD, he joined Colin Pillinger's group at the Open University where he learned stable isotope mass spectrometry, made acid residues of several ordinary chondrites, and used stepped combustion to show that both presolar grains and isotopically anomalous organic matter were present in them, not just in carbonaceous meteorites. In 1989, he moved to Washington University to work with Robert Walker and Ernst Zinner in this new and exciting field (Figure 2). While at Wash. U., he very rapidly became an expert in yet another analytical technique—secondary ion mass spectrometry—and used it for several foundational studies: he showed that presolar SiC grains could be found in situ, without harsh chemical treatments, in meteorite sections via x-ray mapping in the scanning electron microscope; he demonstrated that the isotopic properties of presolar SiC were similar across several different carbonaceous and ordinary chondrites; and he played a key role in the discovery of presolar oxide grains.

In 1994, Conel accepted a staff scientist position in the Carnegie Institution's Department of Terrestrial Magnetism (DTM, now the Earth and Planets Laboratory, EPL), where he has spent the bulk of his career. While he continued to work on presolar grains (largely in collaboration with me once I arrived as a postdoc and then became his colleague as well as with a long series of postdocs, Figure 3), it was at Carnegie that he also began to work in earnest on what would become a big focus of his scientific work: the origin of chondrules, their relationship to other chondrite components, and what they mean for the early evolution of the Solar System. He used the newly installed ims-6f ion microprobe at DTM to investigate trace element abundances and isotopic compositions of chondrule components and developed numerical models of evaporation and condensation to understand the data. He demonstrated that volatile loss from chondrules is not accompanied by isotopic fractionation and showed that this is best explained if chondrules formed in nebular regions with very high densities of solids. Many of the widely accepted constraints on the physical and chemical conditions of chondrule and chondrite formation stem directly from Conel's many important papers on the subject. In recent years, he has published several detailed and extensive analytical and modeling studies aimed at exploring whether chondrule-matrix complementarity exists and at explaining the bulk elemental and isotopic fractionations observed between different chondrite groups based on mixing of small numbers of components.

The third main pillar of Conel's scientific work after presolar grains and the origins of chondrites and their main components has been his dogged pursuit of the origin of organic matter and water in the Solar System. For two decades, he has been producing high-purity insoluble organic matter residues (the major reservoir of carbon in primitive astromaterials) from well over 100 chondrites and collaborating with many people to study them by a huge range of bulk and microanalytical techniques to tease out their isotopic, elemental, and structural properties. Through such large systematic studies, his work has demonstrated the diversity of origins and processing histories of meteoritic organic matter and shown the way towards disentangling effects of parent-body processing from presolar or nebular processing and towards understanding the origin of astrobiologically important soluble organics like amino acids. By systematically analyzing H isotopes of bulk meteorite samples and organic residues, Conel has revealed important trends in the isotopic composition of water across the early Solar System. This work has laid crucial groundwork for the analysis of the first samples returned directly from carbonaceous asteroids by the Hayabusa2 and OSIRIS-REx spacecraft and has profound implications for our understanding of the nature and origin of the water and organic molecules that formed the raw ingredients for the eventual origin of life on Earth.

Conel has published over 230 scientific papers, so in a brief citation I cannot hope to cover all his contributions. In his supporting letter, Prof. Harold Connolly wrote: “The vastness of Dr. Alexander's significant contributions is more than impressive. He has moved in and out of so many different scientific problems in our field and used so many different tools, either analytical or modeling techniques, that I could spend pages going through them all and explaining the significance of so many of his publications in changing the way we performed science in our field or think about the larger-scale issues.” In addition to his scientific contributions, Conel is a remarkably thoughtful, generous, and humble man. He has been my and many others' go-to source for answers about anything cosmochemical for more than 30 years and an extremely enjoyable person to collaborate and socialize with. He loves cycling and dogs and is a loving husband, father, and friend to many. Mister President and members of the Meteoritical Society, I am honored to present Dr. Conel Alexander as the 60th recipient of the highest award of our society, the Leonard Medal.