On January 3rd, 1976, I returned to Switzerland after a 15 month sojourn in South America, mostly spent in Guayaquil, Ecuador, but also by traveling around the continent, including an unforgettable trip to the Galapagos Islands. Two and a half years earlier, I had obtained my diploma in Physics (today we would call this a Master’s degree) at the Swiss Federal Institute of Technology in Zürich (known to everybody as ETH Zürich). My diploma thesis was on a topic in infrared spectroscopy. After that, I felt the need to broaden my horizons, so I took a two semester Interdisciplinary Postgraduate Course on Problems in Developing Countries, again at ETH. This included a work experience in Ecuador, where I did programming work in a company planning a dam for irrigation and hydroelectric power generation. I was always a bit sceptical whether what I did made much sense, but the engineers in Guayaquil seemed happy with my work and asked me to continue a few months beyond the official internship.
Back in Switzerland, I had to start thinking about my future, which thus far I never had done really seriously. I first requested documentation from the International Committee of the Red Cross in Geneva for possible positions abroad, but did not apply. I also looked at the Institute of Photography at ETH, which offered a position for a doctoral student, but I did not apply there either. Yet, less than a month after my return, on February 1st, 1976, I began the work that I do to this day and that has shaped my life: I became a doctoral student in Peter Signer’s noble gas laboratory at the Earth Science Department at ETH. How did this happen so quickly?
In the gymnasium (more or less the equivalent to high school level in the UK or the US) I had developed a fairly serious interest in physics, quite different from chemistry, which I never really liked. My decision to study physics was therefore pretty straightforward, and it was also clear to me that I should do this in Zürich, close to the place where I grew up and continued to live with my parents. At ETH I developed a certain interest in astronomy, though without being able to claim that this shaped my path to the exploration of the solar system with meteorites.
This path I encountered much more fortuitously. Christoph Schuler, a friend from my student days, was about to finish his diploma thesis at the isotope laboratories of the ETH Earth Sciences. He informed me that in Peter Signer’s group a graduate student named Urs Frick had just finished his dissertation and joined John Reynolds’ team at the University of California in Berkeley. I immediately called Peter (Professor Signer at the time, of course) and was invited to visit a day or two later. My soon colleagues to be, Heiri Baur, Herbert Funk, and Philippe Etique, first showed me the lab, which left me terribly impressed. In particular, the mass spectrometers and gas extraction lines with all their piping looked so confusing that I became hesitant about ever being able to operate any of them myself. But Peter Signer’s competent and friendly manner convinced me. YES, I would want to study noble gases in lunar samples. A few days later Peter informed me that I would be accepted, and so it was that I became a doctoral student in his group (note that ETH does not award PhD degrees but Doctoral degrees, so there are no PhD students at ETH).
Apart from the obviously good ambiance in Peter Signer’s group, there was another even more compelling reason for my choice. Peter had explained to me the group’s programme of studying noble gases from the solar wind implanted in lunar samples. Wow, to work with real matter from the Moon, brought back just a few years earlier between 1969 and 1972 by the Apollo 11 astronauts and their later colleagues! And, “solar wind” meant something special to me. Neil Armstrong and Buzz Aldrin had not only collected lunar dust and rocks, but, more importantly for a young Swiss scientist, had also exposed a piece of aluminum foil to the solar wind for 77 minutes to collect noble gases (Geiss et al., 2004). Johannes Geiss at the University of Bern had convinced NASA to carry this foil on board the Apollo 11 as one of only three scientific experiments! This made Johannes the most famous scientist in Switzerland at the time and was the reason why I knew that something called solar wind existed. Seven years later the prospect of being able to work on precisely this topic made it clear: YES, this is what I want to do. Only later did I learn that Peter Signer actually had been the first to propose an experiment to trap solar wind noble gases in a foil exposed in space beyond Earth’s magnetosphere. He and his colleagues in Bern suggested that this might be done on a mission in preparation of the lunar landings or on the Moon itself (Signer et al., 1965), an idea eventually realised by Geiss and his team (see Section 2.2).
So, less than a month after my return from South America, I started my life as a doctoral student in Peter Signer’s noble gas laboratory among my fellow scientists Heiri Baur, Uwe Derksen, Philippe Etique, Herbert Funk, and Peter Horn. Figure 1.1 shows us celebrating the analysis of the 100th lunar sample with the then new noble gas extraction line conceived by Urs Frick. The figure also shows one of the two mass spectrometers we used back in the 1970s. They had been brought to Zürich by Peter Signer from Al Nier’s laboratory in Minneapolis, where Peter had spent seven years. The sector field mass spectrometers designed by Alfred O. C. Nier, the “father of modern mass spectrometry”, enabled new fields of science such as geochronology, isotope geochemistry, and many more (De Laeter and Kurz, 2006). I remember a visit of Al Nier in Zürich on his way to a ski holiday in the Alps. Like probably everyone else who was fortunate enough to meet Al, I was very impressed by his kindness and the genuine interest he showed in my work as a young graduate student. As do really great scientists, he made me feel as if we were speaking at eye level.
Section 2 is devoted to studies of “solar” noble gases, mainly those implanted by the solar wind in lunar and meteorite samples and artificial targets exposed by the Genesis space mission between 2002 and 2004. My own work and that of many of my closest collaborators, including students and postdocs, spans a long period of time, from the start of my doctoral thesis in 1976 until well after my formal retirement in 2014. I will start with some solar noble gas basics and a few historical reminiscences.