Michael Alan Jura, outstanding astrophysicist and a human being concerned about the future of humanity and our planet, died in Los Angeles on 31 January 2016, as a consequence of a rare neuromuscular disease.
Michael was born in Oakland, California on 11 September 1947. After obtaining his bachelor’s degree in physics from UC Berkeley in 1967, Michael moved across the country to pursue a PhD degree in astronomy at Harvard University. His early papers, a few written in collaboration with his thesis advisor Alex Dalgarno, but mostly as sole author, focused on the theory of the diffuse phases of the interstellar medium. Already at the outset of his career, Michael established a pattern of sole authorship that characterized his research career to the very end. This is quite unusual given that sole authorship in astronomical research has become almost a lost art.
Michael's PhD degree, received in 1971, was followed by a two-year stint in the army. He then went to Princeton as a postdoctoral scholar and then to UCLA in 1974 as an assistant professor where he remained for the rest of his career. It is safe to say he had more influence on building UCLA Astronomy to its prominent position today than anyone else in the history of the department.
Michael's early, fundamental papers describe the formation, destruction, and excitation of interstellar molecular hydrogen that is, along with atomic hydrogen, the dominant constituent of the interstellar medium. These papers are still regularly cited more than 40 years after publication. More generally, during the 1970s Michael’s principal research interests were the gas and dust in the interstellar medium of our Milky Way Galaxy and of other galaxies.
Beginning in the mid-1970s, Michael’s focus shifted toward mass loss from giant stars about which, over a period spanning 32 years, he published some 70 papers. One of Michael’s most lasting contributions was his use of infrared all-sky surveys – especially the Infrared Astronomical Satellite (IRAS) catalog – to systematically characterize the lifetimes, space densities, and mass-loss characteristics of red giants of all types. His expertise on dust properties and dust emissivity served him well, as he used infrared spectral energy distributions to draw inferences about the role of dust in driving winds of giant stars and about the return by such winds of nucleosynthetically enriched material to the interstellar medium. He concluded that carbon stars with the highest mass loss rates are responsible for half of the mass returned locally by giant stars to the interstellar medium; the far more numerous oxygen-rich giant stars are responsible for the other half. In addition to drawing broad conclusions about mass loss, Michael’s research on circumstellar environments included studies of photochemistry, dust formation and growth, accretion onto binary companions, systems having bound, dusty disks, and elemental and isotopic abundances.
By the early 1990's, Michael's scientific interests began to shift toward extrasolar planetary systems that orbit main sequence stars. His focus was on dusty debris disks; these are the observational manifestations of the collisional destruction of Kuiper Belt and asteroid-like objects. This was Michael’s first serious encounter with extrasolar asteroids; as described below, his later world-leading investigations of asteroids orbiting white dwarf stars led to an asteroid – 6406 Mikejura – being named in his honor.
Michael identified the dustiest main sequence A-type star in the IRAS catalog, the iconic HR 4796A. His series of papers laying out the HR 4796 planetary system architecture and the properties of its constituent grains served as an essential guide for those entering the field on how to think about debris disks. Michael first demonstrated the decay of small-body populations via collisional grinding by examining the infrared excess properties of A-type stars in the Bright Star Catalog. Michael was an early proponent of the role of stellar winds in clearing debris disks around low mass (M-type) stars and young solar-like stars.
Because of his wide-ranging astronomical expertise, Michael was heavily involved in the design of various NASA space missions. Already in 1976, as a young Assistant Professor, he was invited to join a Goddard Space Flight Center proposal team led by Jack Brandt as a Co-Investigator to help develop a concept for a first-generation Hubble Space Telescope instrument, the then High-Resolution Spectrograph. Michael and Blair Savage were recruited to write a chapter describing the interstellar medium (ISM) science case. Their chapter was so excellent that the proposal team put it at the beginning of the proposal. Indeed, the Goddard High Resolution Spectrograph was selected over other possible science instruments in no small part because the ISM science case was so strong. Subsequently, in 1984, Michael was selected to be an Interdisciplinary Scientist planning for the then Space Infrared Telescope Facility that later morphed into the fabulously successful Spitzer Space Telescope that is still operational today.
In the mid-2000s Michael’s principal research interest shifted from planetary systems around main sequence stars and giant stars to planetary systems that orbit white dwarf stars, which represent the final stage of stellar evolution for most stars. During the last decade of his life Michael devoted almost all of his research efforts to the study of white dwarfs that are accreting minor planets (mostly asteroid analogs) from their surrounding planetary systems. Michael demonstrated that the consequent “pollution” of white dwarf atmospheres provides an exceptionally sensitive method for studying the compositions of rocky planets in extrasolar planetary systems. The information so gathered is not accessible to other astronomical techniques, and was completely unanticipated. We think that Michael found this combination of surprise and sensitivity to be supremely attractive and thus his love for, and total devotion to, such research. Arguably, Michael has contributed more to our understanding of white dwarf planetary systems – and what such systems can tell us about all planetary systems including our own – than anyone else in astronomy.
Michael’s nature as a sensitive, caring person was manifested in many ways. His concern for and encouragement of his peers, junior colleagues, and students was remarked upon over and over by participants in a September 2016 scientific symposium held at UCLA in his honor. Michael was also deeply concerned about the damage our species is doing to the biosphere. At a personal level he walked the walk. He and his wife Martha were early adopters of solar PV panels and an electric car and they early-on removed thirsty plants from their outside yard. Michael walked and used public transportation whenever possible – he was expert on getting around Los Angeles on buses and trains. Michael’s departmental website included an "Energy" component where he gave qualitative and quantitative advice to anyone who happened to log on. For years he argued for implementation of more environmentally friendly measures on the UCLA campus. Michael taught a wide variety of astronomy and physics courses, as well as environmental/energy courses (these latter with various faculty members). He is greatly missed by his colleagues at UCLA and around the world.
Photo: Qingzhu Shi