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Volume XXXI, Issue 32


Table of Contents

1. Obituary for Dr. Dietrich Hovestadt (1932-2024)


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Obituary for Dr. Dietrich Hovestadt  ( 1932-2024)

From: Berndt Klecker, Manfred Scholer, Gerhard Haerendel (berndt.klecker at mpe.mpg.de)

On May 8, 2024, our long-time colleague and friend Dr. Dietrich Hovestadt passed away at the age of 91 in his hometown of Münster. He was one of the leading scientists in the field of near-Earth plasma physics at the Max-Planck-Institut für extraterrestrische Physik (MPE). After studying physics with a focus on nuclear physics in Freiburg, Munich and Hamburg, he received his doctorate at the Technical University of Munich and came to the MPE in 1965. With the participation in the first German research satellite (AZUR) to study the magnetosphere, the MPE had the opportunity of a first satellite project. In his working group at the MPE, Dieter Hovestadt developed several sensors for measuring protons, alpha particles and electrons in the Earth's radiation belt. AZUR, which was launched in 1969, was a great success with detailed measurements of the distribution of protons and electrons in the radiation belt and the study of the entry of energetic solar protons over the polar caps. 

An improved version of the proton-alpha telescope was used on the ESRO-4 satellite (1972-1974). With this experiment it was demonstrated for protons and helium that energetic neutral atoms (ENA) are generated by charge exchange of energetic radiation belt ions with neutral exospheric hydrogen. Independent of the magnetic field, ENAs propagate into lower altitudes and interplanetary space. This mechanism, the effect of charge exchange of energetic protons to ENAs, became years later the basis of a new method to derive information about the large-scale structure of the magnetosphere from energetic neutral particle measurements.

During this time, Dieter Hovestadt and his group at MPE were also developing novel low-energy particle detectors using proportional counters, which allowed the measurement of the energy and mass of the particles at significantly lower energies than when using semiconductor detectors. These novel sensors were integrated into experiment packages over many years of close cooperation with George Gloeckler at the University of Maryland. Jointly with him, he was Principal Investigator (PI) of experiments for the missions IMP-7 (1972), IMP-8 (1973), ISEE-1 (1977), and ISEE-3 (1978), through which he quickly became internationally known. For the first time, the energy, mass and ion charge of energetic ions in near-Earth space could be measured in the sub-MeV energy range. In addition to numerous other results, in 1973 a new component of cosmic radiation was discovered that was neither of solar nor galactic origin. Also new was the measurement of the charge state of solar ions on ISEE-3. With this knowledge, one could decide between competing mechanisms for accelerating the ions. ISEE-3 measurements of energetic ions at low energies revealed for the first time the flows of plasma structures in the distant tail during geomagnetic activity. With ISEE-1, the acceleration of ions at the Earth's bow shock could also be examined in detail.

Of course there were also failures. For the Russian Mars missions Phobos-1 and Phobos-2 (launched in July 1988), Dieter Hovestadt, as PI, developed an experiment (ALPHA-X) to analyze the surface composition of the Martian moon Phobos using alpha and X-ray backscattering. Unfortunately, the experiments could not become operational, because contact with Phobos-1 was lost shortly after launch and with Phobos-2, while already in Mars orbit (March 27, 1989).

The disappointment was big, but was tempered by Hovestadt's optimism, his ability to motivate the working group, and by the prospect of the MPE's participation in the SOHO and CLUSTER missions, which were to be realized as the first cornerstone of the ESA "Horizon 2000" program. In fact, the Hovestadt group was able to contribute to the four Cluster satellites the CODIF sensor as part of the CIS sensor package for the determination of plasma dynamics. This was done in close collaboration with CESR and UNH with the PI H. Rème (CESR, Toulouse). After the launch failure of Ariane 5-1 in 1996, satellites and instrumentation were rebuilt with financial support from ESA, successfully launched in 2000, and still successfully operational.

Between 1987 and 1995, under the direction of Dieter Hovestadt (PI 1987-1995) the CELIAS instrument for the Solar Observatory SOHO was developed in international cooperation. The task of the four CELIAS sensors was to determine the element, charge and isotope composition of the slow and fast solar wind, of solar and interplanetary suprathermal particles, and of low-energy ions of solar and interplanetary origin. Launched in 1995, CELIAS was a complete success, documented by more than 150 publications by the CELIAS team in peer-reviewed scientific journals, as well as by more than 750 publications in which CELIAS data were used. After his retirement in 1997, he followed the results of the experiment with great interest.

Dieter Hovestadt was not only a very good experimental physicist, but also an excellent mentor. He knew how to motivate his employees and especially encourage his young colleagues to take responsibility by engaging in new developments or leading projects, all under his continued support. Furthermore, his rich personality, independent thinking and joy in socializing made him a real asset to share an acquaintance or friendship with.

His death is a great loss for science and for the large number of friends he made while collaborating with many groups at home and abroad. We will miss him.

He leaves behind his wife Helga, his son, Philipp, his daughter, Marlies, his stepdaughters Nicole and Denise and several grandchildren.


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