Donald M. Hunten

Donald Mount Hunten
March 1, 1925 - December 14, 2010

Statement from the Lunar and Planetary Laboratory, University of Arizona
December 21, 2010
Reposted from

On December 14, 2010, LPL lost Don Hunten after a long illness. During his last days, Don was tended with loving care by our colleague and his wife and colleague, Ann Sprague.

Don's scientific career began with the study of physics at McGill University, where he obtained a doctorate in 1950. While a faculty member at the University of Saskatchewan his research concentrated on the study of aurorae. By 1963 however the space age was starting in earnest. At the invitation of Joe Chamberlain, Don moved to Kitt Peak National Observatory in Tucson (now NOAO) to join the newly formed space research group and his main interests switched to the study of planetary atmospheres. Thus, Don joined the first group of pioneers in the scientific exploration of the solar system and he was to be a leading figure in this community for nearly half a century.

The accomplishments of these pioneers were remarkable, including the first characterizations of the atmospheres in our solar system along with development of the basic understanding of the structure and chemistry of these atmospheres and the experimental and theoretical tools used to study them. Many of the ideas developed during that time are still with us today and Don's contributions were central to their development. A signature achievement during this phase of Don's career was an understanding of how odd hydrogen chemistry stabilized the atmosphere of Mars against destruction by photodissociation. Don moved to the Lunar and Planetary Laboratory of the University of Arizona in 1974 and his involvement in planetary research continued unabated. He also taught numerous students and post doctoral associates. Don retired in 2001, but remained active until recently. He received many honors during his career, including induction into the National Academy of Sciences, the Kuiper Prize of the Division of Planetary Sciences of the American Astronomical Society, and a Regents' Professorship at the University of Arizona.

One of Don's most far reaching achievements concerned the role of diffusion in atmospheric escape processes. "Hunten's Principle," as this is sometimes known, described how the escape rate was limited by diffusion of the escaping species through the background atmosphere. The theory was beautiful in its clarity and showed how the escape rate was independent of many complicating factors, chemistry, vertical mixing, etc. and led to a simple and accurate formula. Typically for Don, the theory was formulated in response to an observation, the detection of molecular hydrogen in Titan's atmosphere, when it was expected to have a very low abundance because of rapid escape. The theory was developed in a series of papers in 1972-1974 including an application to the escape of hydrogen from the terrestrial atmosphere---one of the best examples of how studying other planets leads to a better understanding of our own.

Don was a major influence on the unmanned space program with involvement in the planning and execution of numerous NASA planetary missions including Pioneer Venus, Voyager, Galileo and Cassini. In fact, Don was the godfather of so many mission that some of us took to calling him "The Don." I'm not sure that he knew, but I don't think that he would have minded. In addition to his direct involvement on the experiment teams, Don help conceive these missions, argued for their funding, sat on (and often chaired) their planning committees, helped to define the scientific goals, and provided wise guidance during their execution. The scientific legacy is enormous.

Don was a scientist of extraordinary breadth. His expertise ranged across the planetary sciences from chemistry to remote sensing to thermal processes to studies of atmospheric evolution and he used a variety of tools including telescopic observations (often with instruments that he designed and built himself), spacecraft observations, and theoretical investigations. With a penetrating intellect and an encyclopedic memory, Don would get to the heart of a problem with a speed and precision that sometimes left the rest of us feeling rather embarrassed and dull-witted. A talented tinkerer, Don could build a harpsichord in his garage, or repair your PC with the needle-nosed pliers and soldering iron that he kept in his office, all the while with gentle classical music playing in the background. He wrote nearly as many papers on electronics as he did on atmospheric evolution. Content for most of his career to work out results analytically, or employ code-savvy younger scientists for calculations, Don waited until he was nearly 80 years old to learn fortran programming, because, I suspect, he finally had the time. May we all maintain such intellectual ambition.

Throughout his career, Don went out his way to support and encourage younger scientists. He was extremely generous with his time, advice, and insight. As a result, Don leaves behind legions of students and collaborators that he profoundly influenced. These intellectual disciples can be found in every planetary science research center on the globe. Don's textbook, co-authored with Joe Chamberlain, "Theory of Planetary Atmospheres," was the bible for many of us. This pales though, in comparison to personal interactions, through which Don could more directly impart his common sense approach to planetary science. Those of us that were fortunate enough to be exposed to this wisdom received an extraordinary gift and will miss him greatly. His spirit lives on in the work that we do.

Distributed by Athena Coustenis, Division for Planetary Sciences, American Astronomical Society:

Donald Mount Hunten passed away on the 14th of December, 2010. He was born in Montreal, before his family moved to London, Ontario where Don attended the Western Ontario University In 1946 he enrolled in the Ph.D. program at McGill University, back in Montreal, where he obtained his PhD in 1950. He later became assistant professor at the University of Saskatchewan. After Joe Chamberlain moved to Kitt Peak National Observatory in Tucson to form a space research group, he invited Don to join it and so Don moved to Tucson. In 1974 he became professor at the Lunar and Planetary Lab. In 1982 he was inducted into the National Academy of Sciences and he eventually became a Regents Professor at LPL, UA. Borrowing from a citation by T. Owen at the 1998 John Adam Fleming Medal of the American Geophysical Union honoring Don:

"Donald M. Hunten is a model for all of us engaged in the study of planetary atmospheres. He is first of all a superb scientist, one of the finest aeronomers our planet has produced. He is that rare combination of instrumentalist, observer, theorist, and responsible representative of his field that makes a 'compleat' scientist. Don's contributions are evident everywhere in the record of terrestrial and planetary aeronomy. In the 1950s, he was preeminent among those who developed the ground-based instruments that obtained the spectra required for an understanding of the excitation of Earth's airglow and aurora, and he also developed the theories that explained the data. In the early 1960s, he contributed to the deflation of the Martian atmosphere by demonstrating the weak points in earlier attempts to derive the red planet's surface pressure. Don was the godfather of the Pioneer Venus mission and a key scientist in its highly successful implementation and the analysis of the results. One of his greatest achievements was the development of the theory of diffusion-limited escape and the subsequent analysis of escape of hydrogen from the planets. Turning to the outer solar system, Don developed a model for the atmosphere of Titan prior to the Voyager 1 encounter in 1980 that was so good it became the standard after the data came in confirming it. With his extraordinary intuition and insight, he had correctly surmised that Titan must have a massive, molecular nitrogen atmosphere, well before there was any detection of N or N2 on this intriguing satellite. In the following decade, Don used his excellent grasp of physics together with his extensive experience in deep space missions to play a critical role in the design of the Cassini-Huygens mission, now safely on its way to Saturn and Titan."

Don Hunten also worked on the analysis of data from the Galileo Probe into Jupiter's atmosphere and investigated the tenuous, gaseous envelopes around Mercury and the Moon. He has been an inspiration and a mentor for many of the currently confirmed planetologists.

An Autobiographical Comment
Don Hunten, November 12, 2010:

I was born in Montreal, where I spent my first three years, and we then moved to London, Ontario where my father had obtained a chemistry professorship. Before long he designed and built a cottage at Rondeau on Lake Erie where we spent many happy summers. I became a choirboy and from the age of 6 took piano lessons. After I finished high school I attended my father’s university, Western Ontario. I took a program in chemistry and physics because I was interested in both subjects, but the third-year organic chemistry lab convinced me to become a physicist. These were war years, and we spent three hours every weekday in the University Air Squadron, then in the last year the Canadian Officers Training Corps. In my senior year the war was over and we could spend full time on our studies. I was not becoming a good pianist and switched to clarinet and many years later switched again to the bassoon. I then (1946) enrolled in the Ph.D. program at McGill University, back in Montreal, where I saw a lot of my Auntie Dolly. Graduate students normally were also employed as "demonstrators", lab assistants, and it was in the Electricity and Magnetism lab that I met Ann Rubenstein. When I later met her family I learned that those students called me "flannel feet" (a radio character) on account of my rubber-soled shoes. Ann took a shine to me, and I enjoyed many dinners and bridge games at her parents' house and cottage on beautiful Lake Memphremagog to the southeast on the Vermont border. Shortly before I obtained my PhD in 1950, we were married, Ann took a job with the Red Cross blood transfusion service, and we took residence in a one-bedroom apartment

I wanted a university job in Canada, and the only one I found was as a post-doc at the University of Saskatchewan. We bought an old car and drove to Saskatoon. I started lecturing along with my auroral research, and soon became an assistant professor. Ann had always been interested in fossils, so after her chemistry degree from McGiill she started taking geology courses. She did not get another degree because women were not allowed to take the field trip. She also gave birth to Keith and Mark in 1962 and 1964.

My initial job was supported by a huge (for those days) contract from the U.S. Air Force. The contract monitor was Joe Chamberlain, and this led to our first acquaintance. Later he joined the Yerkes Observatory of the University of Chicago, which had another USAF contract for auroral research, and we collaborated. In 1963 he moved to Kitt Peak National Observatory in Tucson to form a space research group and invited me to join it. I took a 3-year leave of absence from the University, and got so involved with NASA that I decided to stay in Tucson.

By 1964 most of our group, including Joe, had left. I noticed that the Lunar and Planetary Lab next door was getting very good, and I asked for, and received, a professorship. At about this time I was urged by several colleagues to take a temporary job at NASA Headquarters in Washington and I spent six months there. In 1982 I was inducted into the National Academy of Sciences and I eventually became a Regents Professor at LPL, UA.

One of my students was Ann Louise Sprague, and after she obtained her PhD she moved to a NASA center for a year. She then requested a post-doc job back in Tucson and we engaged in an extensive telescope-observing program. We fell in love. I left Ann Hunten who divorced me. Ann Sprague and I were then married. We bought a house in the Starr Pass area of Tucson, which we sold in 2010 so that we could move to the retirement community of Quail Creek. Two years previously I had a stroke that paralyzed my left side. After much effort, physical therapy, and loving encouragement I considerably recovered; able to walk with a walker but with a left arm and hand still weak.

Addendum by Ann Sprague, December 15, 2010:

Don suffered another devastating stroke on 23 Nov 2010. He painfully left his family, friends, Science, and this Earth at 3:45 a.m. the fourteenth of December.

A Personal Remembrance by Mark V. Sykes, December 18, 2010:

We have lost another major figure in our profession with the passing of Don Hunten. I was Don's first student to graduate from LPL back in the 80s and I shall miss him very much. In addition to being a noted and admirable scientist, Don was a fine musician, playing early music on wind instruments with the University's Collegium Musicum. He even built a harpsichord. Don was unstintingly generous of his time and resources to graduate students when I was in the department. He would often use his own grant money to pay for the travel of other faculty's students to the DPS (and I am not talking about 1 or 2, but 5 or 7!). He was broadly knowledgeable and as my advisor put up with (and financially supported) my own forays into subject areas outside his own discipline of planetary atmospheres. He was patient, but would not stand any bloviating. He was a favorite target of imitation by students and others in the field - and I fondly remember doing his voice in a cart covered with his blue sweater in the grad student skit "Hunten's Brain" (a huge cauliflower, set within a fog of carbon dioxide, with wires coming out, one into his Pioneer Venus coffee cup, and surrounded by walnuts representing the brains of former graduate students). Don continued to be scientifically productive through strokes, publishing single-author papers in Nature and Icarus until just a couple of years ago. His body finally failed, but his mind never did.