J. Mayo Greenberg, a leading experimental astrochemist and expert on cometary structure and composition, died of pancreatic cancer in his home in Leiden, The Netherlands, on 29 November 2001. Though born in Baltimore, Maryland on 14 January 1922, and educated at Johns Hopkins University, Greenberg had immigrated to The Netherlands in 1975, and it was there that his cometary expertise matured.
Greenberg was an exceptional child, entering Johns Hopkins University to study physics when he was only fifteen years old, and advancing to graduate studies, also in physics, in just over two additional years. His academic career was interrupted by war-related research during the 1940s, but Greenberg returned to Johns Hopkins to complete his PhD in 1948 with a dissertation on the scattering of radiation by matter. During his academic career in the United States, Greenberg held appointments at the University of Delaware, University of Maryland, Institute for Advanced Study at Princeton, Rensselaer Polytechnic Institute, Dudley Observatory and The State University of New York at Albany, where he served as chairman of the physics department.
Greenberg’s interests gradually broadened from theoretical to experimental work while at the same time his interest in astronomy, in particular the problems related to how scattering processes polarized, reddened and blocked light in space, continued to deepen. A sabbatical year, and a year as a visiting professor, both at Leiden and in close contact with Henk van de Hulst and Jan Oort who had similar interests, were sufficient to persuade Greenberg that relocation to The Netherlands would be of interest. When van de Hulst persuaded Leiden University to invest in a chair for laboratory astrophysics, Greenberg was a natural choice for the position. Greenberg moved to The Netherlands in 1975, and resided in Leiden for the remainder of his life. Until his retirement in 1992, Greenberg was director of the Huygens Astrophysical Laboratory at Leiden University.
At Leiden, Greenberg’s achievements included the laboratory synthesis of complex organic molecules from smaller molecules under laboratory conditions simulating those prevailing in space. He went on to demonstrate that such molecules evolved into even more complex refractory organic molecules when exposed in space to the actual radiation that exists there. Samples of laboratory produced “yellow stuff” changed, after exposure in actual space conditions, into a dirty brown colored material. Space missions to Comet Halley determined that this color emulates the actual surface of that comet, while spectroscopic studies confirm that the two exhibit similar molecular structures. The question of the possible origin of life on earth as we know it fascinated Greenberg. In his laboratory he was able to demonstrate that space conditions not only permitted the synthesis of complex molecules on the surface of dust particles, but also that those molecules could be produced in stereospecific forms by the strong, circularly polarized ultraviolet radiation in dusty gas clouds surrounding neutron stars. The recent discovery of stereospecific forms of organic molecules in space provided a solid confirmation of this elegant laboratory research.
In the past quarter century, as George K. Milley described it in an internet tribute to Greenberg posted immediately after he died, “…the laboratory that Greenberg created has produced a constant stream of fundamental research papers, and cultivated a series of brilliant students who have gone on to be scientific leaders themselves. Although the Leiden Laboratory was the first such facility, there are now several comparable laboratories throughout the world, some of which are led by ex-students or staff of the Leiden Lab.”
In 1947, Greenberg married Naomi Slovin, who survives him together with their two daughters, two sons and grandchildren.
This obituary essay is drawn from both a copy of Milley’s internet tribute (http://www.strw.LeidenUniv.nl/mayo.mayo.html) provided by Naomi Greenberg, and from a lengthy and excellent obituary published in the International Comet Quarterly (Marcus, Joseph N. “J. Mayo Greenberg (1922–2001)”, 23, 4(2001 October):153-155). The latter covers Greenberg’s extensive contributions to comet theory and provides a useful list of relevant technical literature in astronomy, astrophysics and astrobiology.