Saturn’s Huge Moon Titan Drifting Away Faster Than Previously Thought

Report from ISSI Team #411 The ENCELADE Team: Constraining the Dynamical Timescale and Internal Processes of the Saturn and Jupiter Systems from Astrometry led by V. Lainey

Did you know that the Earth’s moon distance is increasing at about 3.8 cm/year because of the tides the Moon raises on our own planet? Thanks to Newton and his law of gravity, entailed the proper explanation of tides: the side of the Earth that is closer to the Moon is more attracted than its opposite side. As a consequence, the Earth takes an elongated shape like a football. Distance increase comes then as a consequence of friction inside the oceans essentially. Both shape distortion and orbital variation rate are expected to get significantly lower with distance, since tides are a consequence of gravitation.

A giant of a moon appears before a giant of a planet undergoing seasonal changes in this natural color view of Titan and Saturn from NASA’s Cassini spacecraft. (Image Credit: NASA/JPL-Caltech/Space Science Institute)

Since tidal theory is universal, researchers have applied it over the last 50 years to predict the orbital evolution of many moons. From the evolution of the four big Galilean satellites of Jupiter to the small moons of Mars, Phobos and Deimos, the same theory was used underneath. Recently and in the context of the Cassini mission, the ISSI ENCELADE Team led by Valery Lainey in collaboration with a team from the University of Bologna tried to quantify from observations the orbital expansion of Titan, the largest Saturnian moon, under Saturn’s tides. Surprisingly, they found that Titan is escaping Saturn’s gravity at a large pace of 11 cm/year, more than a hundred times faster than expected from theoretical models. Even more surprising, such expansion rate is larger than for moons closer to Saturn, in complete contradiction with classical tidal theory! But the study demonstrates a perfect agreement with the prediction of a new tidal mechanism, suggested only four years ago by Jim Fuller (Caltech) and co-authors. Such so-called “tidal lock mechanism” suggests that Titan may have formed way closer to Saturn, than commonly believed. This result brings an important new piece of the puzzle for the highly debated question of the age of the Saturnian system.

Like the classical tidal theory for terrestrial objects, tidal lock mechanism is a universal physical mechanism for giant planets. In principle, it could be at play in way other systems were giant planets are involved, starting with the Jupiter system itself.

More Information can be found here: News Release June 8, 2020, NASA JPL Caltech >>

Lainey, V., Casajus, L.G., Fuller, J. et al. Resonance locking in giant planets indicated by the rapid orbital expansion of Titan, Nature Astronomy, 2020.

New selected International Teams in Space and Earth Sciences 2020

Thirty-two International Teams have been selected by the ISSI Science Committee for implementation from the proposals received in response to the 2020 call. 

As one of ISSI’s and ISSI-BJ’s tools, International Teams of up to 15 scientists address specific self-defined problems in the Space and Earth Sciences, analyzing data and comparing these with models and theories. The teams  work together in an efficient and flexible format with typically 2-3 one-week meetings over two years. The results of the studies are published in the peer-reviewed literature.  

New International Teams 2020 >>

Interviews with Weiqing Han and Sabine Schindler – Johannes Geiss Fellows 2020

Prof. Weiqing Han, University of Colorado at Boulder, USA and Prof. Sabine Schindler, University of Innsbruck, Austria have been elected as the 2020 Johannes Geiss Fellows. Prof. Weiqing Han is a world-renowned oceanographer who specializes in Global Sea Level Change, in particular, in coastal regions. Prof. Sabine Schindler is a highly recognized astrophysicist who specializes in the observation and modeling of galaxies and galaxy clusters. We have tele-interviewed both, asking a few questions about their upcoming fellowships at ISSI.

Prof. Han, Prof. Schindler, first of all, congratulations on your election as the Johannes Geiss Fellows 2020! What was your motivation to apply for the Johannes Geiss Fellowship at the International Space Science Institute? And have you already made plans when you will visit ISSI?

Weiqing Han:  The ISSI has been doing and leading active research in global and regional sea level variability and change, which fits my research interest and has been one of my major research focuses in the past decade. The motivation of my application is to establish collaboration with ISSI, and hope that by combining our effort and working in a simulating environment we can more effectively achieve our research goal.

Sabine Schindler: The International Space Science Institute is well known in the community – and well known to
me – as an excellent place for networking and communication in space science. To spend my sabbatical there with a Johannes Geiss Fellowship seemed ideal to me to expand the connections  to the space science community and to the Swiss universities. I am very happy, that this Fellowship was awarded to me and I am looking forward to my stay in Bern. I plan to start my visit in November.

Could you describe your scientific project(s) on which you plan to work during your visit to ISSI?

Weiqing Han: Rapid sea level rise is one of the most consequential impacts of the warming climate, exerting threats to human society in low-lying coastal areas and island nations. The observed rates of sea level change in the past few decades and century, however, have large spatial differences due to a complex mix of natural and anthropogenic factors. During my proposed visits to ISSI, I plan to investigate the effects of continental shelf and slope on coastal sea level signals that originate from open ocean. This area of research is important, because coastal bathymetry plays a crucial role in accurately depicting open-ocean impact on coastal sea level during historic periods and for future projections. Yet, this information is extremely limited due to the lack of high-resolution, basin-scale datasets and model experiments that can adequately resolve continental shelf and slope.

Firstly, we will analyze tide gauge observations, gridded satellite altimetry data, coastal altimetry data, together with reconstructed and reanalysis sea level products, to understand in which coastal areas a large amount of interior ocean signals can arrive at and be trapped to the coasts. While tide gauges are right on the coasts, altimeter data are contaminated by lands near the coasts. Therefore, the location of altimeter data may be a few tends of kilometers offshore from the tide gauge location. Secondly, we will  analyze large ensemble (LE) and CMIP6 climate model historic simulations, comparing the relatively coarse resolution model results with those of finer resolution ones, which can better represent continental shelf and slope.

Sabine Schindler: I plan to work on extragalactic astrophysics. I have a special interest in galaxies and galaxy clusters for two reasons:Firstly, for the physical processes and interactions that determine their evolution and secondly, for their cosmological applications. I plan to do observations as well as numerical simulations to do study these topics. I furthermore intend to do some interdisciplinary research, if something interesting is coming up in my discussions with the colleagues. I will keep my eyes open in this respect.

Prof. Schindler, is there a particular galaxy (or galaxies) you plan to focus on? And if so, why this particular one?

Sabine Schindler: I usually focus on processes, like e.g. ram-pressure stripping in galaxies or metal enrichment in galaxy clusters. I then select my targets according to the best suitability for a particular question.

Have you been to Switzerland and what – in addition to ISSI – makes Bern appealing to you for a visit?

Weiqing Han: In 2015 and 2018, I was invited to attend the sea level workshops organized and hosted by ISSI, Dr. Anny Cazenave from ISSI and Dr. Detlef Stammer from the U. of Hamburg, which aimed to tackle important but challenging issues toward understanding and projecting global (2015 meeting) and coastal (2018 meeting) sea level changes. On my side, the outcomes of the two meetings are that I led two review articles that were published in Surveys in Geophysics, one for climate modes’ impacts on spatially uneven sea level changes in the world’s oceans (published in 2017) and the other, focuses on impacts on coastal ocean (published in 2019).

Sabine Schindler: I have been to Switzerland before, both for work and for pleasure. I have enjoyed both. There is a very interesting astrophysical community in Switzerland, that I plan to visit. I have also been to Bern before, which I liked very much as a city.

Prof. Weiqing Han, University of Colorado at Boulder, USA                     
Prof. Sabine Schindler, University of Innsbruck, Austria

A Word from the ISSI Executive Director

Dear friends of ISSI,
Dear visitors of our web page,

As you are certainly aware, the COVID-19 crisis is ongoing and although some of the lockdown measures are being lifted or at least alleviated, life is far from having returned to normal. This applies to ISSI as well. Even more, as an international Institute of Advanced Studies, ISSI depends on borders being open and scientists being able to travel!

Of course, we have been considering how we could take better advantage of the chances that working from remote and telecommunication are offering. ISSI committee meetings have been web meetings for two months and will continue for the coming weeks. The Johannes Geiss Fellowship selection has been done remotely, keeping the schedule. As you may have already seen on our web page we have able to select two outstanding scientists, an astronomer and an oceanographer working on Global Change. You are invited to read interviews with the two fellows that will be published on the web in the next few days. ISSI’s science committee is presently evaluating the proposals for International Teams using remote services and the directorate will announce the successful projects in time. ISSI will further improve its technological readiness for tele-meetings by installing hardware that will allow scientists from remote to better follow the discussion in the meeting room.

Conveners of workshops and forums that were originally scheduled to occur in May to August have been offered the opportunity to use telepresence rather than postpone their events. To date, all meeting conveners have emphasized the importance of face-to-face discussion and have decided that they would rather postpone to the fall or next spring. This includes the Venus workshop, the workshop on Strong Gravitational Lensing and that on Magnetic Reconnection as well as the Forum on Ground and Space Astronomy. However, we are committed to have the workshop on the Geophysics of the Deep Earth occurring as the first Workshop after the lockdown. Of, course, it is entirely possible that we will see the first team meeting before that and possibly the first team meeting that will be using remote services. ISSI is committed to provide its service as well as it possibly can and will open as soon as the Swiss authorities allow and as soon as is considered reasonable and safe. Given what is known today, it is likely that certain measures of precaution will be necessary but we are ready to implement what is needed to continue. We are committed to keeping the damage to the program at the lowest possible level!

In the meantime, I hope that you and your loved ones stay safe. You can reach us per email or over the phone at the institute.

Our thoughts and sympathies continue to be with those all over the world hit by COVID 19!

Stay safe and hope to meet you all in person at ISSI sometime soon!

Tilman Spohn

ISSI executive Director

Johannes Geiss Fellowship 2020

The International Space Science Institute ISSI is proud to announce

Prof. Weiqing Han, University of Colorado at Boulder, USA


Prof. Sabine Schindler, University of Innsbruck, Austria

as the 2020 Johannes Geiss Fellows.

Prof. Weiqing Han is a world-renowned oceanographer who specializes in Global Sea Level Change, in particular, in coastal regions.

Prof. Sabine Schindler is a highly recognized astrophysicist who specializes in the observation and modeling of galaxies and galaxy clusters. She has been the vice-rector for research of the University of Innsbruck and rector of the University UMIT Hall.

The Fellowship is named after Prof. Johannes Geiss, the founder of the institute.

ISSI had received more than ten excellent proposals from top level scientists from which the selection committee chose the sixth and seventh JGF recipient after thorough evaluation. The selection committee consisted of the Directors and the Chair of the ISSI Science Committee.

ISSI is honored by the high interest from the science community in the Johannes Geiss Fellowship and would like to deeply thank all applicants.

Obituary Jean-Marie Luton 1942-2020

Jean-Marie Luton (Credit: ESA)

Jean-Marie Luton passed away on 16 April 2020 at the age of 77. He was ESA’s fourth Director General, serving from 1990 to 1997. In that capacity, he was fully involved in the setting-up of ISSI. 

He was born on 4 August 1942, in Chamalières, near Clermont-Ferrand, France. After graduating in engineering from the Ecole Polytechnique in 1961, he joined the aeronomy department of the French national research institute, the Centre National de la Recherche Scientifique (CNRS). Here he worked in geophysics research and on an experiment for the NASA OGO-6 satellite, launched in June 1969 and designed to study the various interrelationships between, and latitudinal distributions of, high-altitude atmospheric parameters during a period of increased solar activity.

He was appointed special research advisor at the French space agency CNES in 1971, and then seconded to the French Ministry of Industrial and Scientific Development. There he participated in the European negotiations that took place in the framework of the European Space Conference which led to the establishment of ESA in 1975, emerging from its predecessor organizations ESRO and ELDO.

As French delegate to the ESA Council, he also served as the Chairman of ESA’s Administrative and Finance Committee. In February 1989, he was named Director General of CNES, a position he left in October 1990, to take up duty as ESA Director General, succeeding Prof. Reimar Lüst who passed away this year on March 31st .

During Jean-Marie Luton’s terms of office as Director General, ESA conducted several successful space science missions. The Ulysses mission, the Infrared Space Observatory (ISO) and the Solar and Heliospheric Observatory (SOHO) and he first servicing mission to the Hubble Space Telescope, were all carried out in the 1990s. During this period, Ariane 4 also successfully launched Meteosat-5 and -6 as well as ERS-1 and -2. He was of great help in resurrecting the Cluster mission which was destroyed during the launch of the first Ariane5 launcher.

When he joined ESA in 1990, he was fully involved in the negotiations with Switzerland to create ISSI, and had frequent meetings with Johannes Geiss, Peter Creola then Swiss delegate to the ESA council and Hans-Peter Schneiter President of the Pro ISSI Foundation. His very positive support to the concept of ISSI and the friendly relationship he developed with his scientific colleagues and administrative Swiss friends until he left ESA in 1997, when he becomes President and Director General of Arianespace, were crucial to quickly create and develop ISSI in its very early days.  

Through his important role in the establishment of ISSI and his long-lasting involvement in the development of European space and Earth science, Jean-Marie Luton has offered to the European and International space research community an essential support, allowing them to take full benefit of ISSI, in a broad field of scientific disciplines, in Solar System exploration, astronomy and Earth sciences.

Roger-Maurice Bonnet, International Space Science Institute

Aliphatic Organics and Ammonium Salts on the Surface of Comet 67P/Churyumov-Gerasimenko

Report from ISSI Team #397 Comet 67P/Churyumov-Gerasimenko Surface Composition as a Playground for Radiative Transfer Modeling and Laboratory Measurements” led by M. Ciarniello

A primary goal of ESA’s Rosetta mission to comet 67P/Churyumov-Gerasimenko (hereafter 67P) was the characterization of the nucleus material.

The Visible Infrared and Thermal Imaging Spectrometer (VIRTIS) revealed a mostly spectrally uniform nucleus surface, dominated by a low-albedo material exhibiting a broad infrared absorption centered at 3.2 µm. The surface composition of the comet was found compatible with a mixture of organics, minerals and minor amounts of ices, although the identification of the compounds responsible for the 3.2-µm feature has remained challenging so far.

Ammonium salts found on Rosetta’s comet (Image Credit: O. Poch, IPAG, UGA/CNES/CNRS (left); ESA/Rosetta/NavCam – CC BY-SA IGO 3.0 (right))


Here we report the results of a refined analysis of measurements acquired by the instrument’s infrared mapping channel (VIRTIS-M-IR).

In particular, spectral signatures of aliphatic organics within the broad absorption band were identified for the first time on a cometary nucleus. In addition, further investigations by means of laboratory experiments allowed the identification of ammonium salts as carriers of the 3.2-µm absorption feature. These salts may be a major reservoir of nitrogen in comets.

These studies highlight similarities between the infrared spectrum of 67P with those of other minor bodies in the Solar System, including some outer belt asteroids and Jupiter Trojans. As a consequence, these bodies may host organic materials and/or ammoniated salts, blurring the distinction between comets and other primitive objects. Aliphatic features in 67P appear similar to the typical aliphatic features in the interstellar medium (ISM) and are also compatible with those of the chondritic insoluble organic matter (IOM). This suggests that the organic material may be inherited from the ISM by comets and other minor bodies that delivered it to the inner Solar System. Similarly, ammoniated salts, potentially formed in the icy mantle of dust grains in the pre-stellar or protoplanetary phases, could have provided nitrogen to the inner planets. Such processes could have favored the emergence of a prebiotic chemistry.

These investigations took advantage, among other authors, of the collaboration of the ISSI Team “Comet 67P/Churyumov-Gerasimenko Surface Composition as a Playground for Radiative Transfer Modeling and Laboratory Measurements” led by M. Ciarniello and have been published in two separate papers:

“Infrared detection of aliphatic organics on a cometary nucleus” by A. Raponi et al., 2020, Nature Astronomy; DOI:

“Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids” by O. Poch et al., 2020,  Science 367, DOI:


Obituary Reimar Lüst 1923-2020

Reimar Lüst (Image Credit: Kurt Strumpf/AP)

Reimar Lüst, of German nationality, astrophysicist, and well known for his work on cosmic rays, plasma physics, hydrodynamics and nuclear fusion, and a pioneer of European space research, passed away during the night of 31st March, in Hamburg where he lived, one week after his 97th birthday. He was the son of a Lutheran Pastor and born into a pious household in the town of Wuppertal-Barmen on 25 March 1923. He attended school in the Kessel gymnasium from 1933 until 1941 when he had to rejoin the Kriegsmarine in the cold water of the Bay of Biscay, serving as a submarine officer. His U-boat N° 528 was severely damaged, bombed and destroyed by a British depth-charge and was going to be sunk to prevent it from getting into the hands of the enemy, drowning eleven men on board. From a depth of 320 m, thanks to his physical strength and some luck, he was able to make it up to the sea surface and then swam for several hours to an English frigate which had attacked the U-boat, before being heaved onto the deck and sent as a prisoner-of-war in a camp, first in England and then in the US at Mexia, Texas, where he stayed until 1945. This was long enough for him to be appreciated by his guards for his mathematical talents, solving calculus problems on toilet paper. That is how he started his brilliant and extraordinary career.

In 1946, he returns to destroyed Germany and is a student at the Johann-Wolfgang-Goethe Frankfurt University where he gets a Diploma in 1949, and in 1951 he becomes assistant of Carl Friedrich von Weizsäcker, brother of the future President of Germany, and Werner Heisenberg (Nobel Prize, 1932) of the Physics Max Planck Institute in Göttingen where he gets his doctorate in theoretical physics under the direction of his two prestigious professors. He then worked in theoretical plasma physics and astrophysics for the next ten years. In 1955, he gets a Fulbright fellowship and rejoins the United States and the Institute Enrico Fermi at the Universities of Chicago and then Princeton, where he worked with John Simpson, Eugene Parker, and James van Allen in Iowa.

In 1956, he becomes the father of Dieter Lüst, well known physicist and cosmologist, presently Director of the Max Planck Institute of physics created by Heisenberg in 1958. He obtains his habilitation in physics in 1959 at the University of Munich, and in the same year his wife gives birth to his second son Martin, Nokia Head of Technology. He then spent several years in the USA as visiting professor at New York University (1959), Massachusetts Institute of Technology (1961) and Caltech (1962). In 1964, he becomes Professor at the University of Munich.

In 1960, following a suggestion of one of his early collaborators, Ludwig Biermann, he realized the potential of space research for astrophysics and Earth sciences. Biermann proposed to directly probe the just-discovered solar wind, using alkali metals ionized by solar radiation creating an “artificial comet” which would then trace the magnetic field carried by the solar wind, and reveal its structure and behavior into interplanetary space, as they would become visible in optical wavelengths and therefore observable from the ground. In 1961, he is committed by the Max Plank Society to leading a working group in charge of founding what would be the future national space program of Germany. Two years later he founds the Max-Planck Institute for extraterrestrial Physics (MPE) in Garching and started developing rocket experiments together with Gerhard Haerendel.

In the post-war context, the development of rockets in Germany was a delicate and sensitive idea. Looking for a possible cooperation with scientists from the war allies, Lüst became a frequent visitor of space science meetings and was able to attract the attention of COSPAR participants, in particular Jacques Blamont, Director of the Service d’Aéronomie near Paris whose program was the study of the Earth upper atmosphere and of the Sun. With Blamont, he developed a true friendship which allowed him to launch from the Ile du Levant in the south of France and from Hammaguir in the Algerian desert, between 1962 and 1966, a series of sounding rockets of the French outfit, including the Centaure and the Véronique (French version of the V2). Both him and Gerhard Haerendel could then test the idea of Ludwig Biermann and were the first to send barium clouds in the upper atmosphere and measure the extension and dynamics of the Earth magnetic field. In the post-war context these experiments would not have been possible without the French hospitality and Lüst’s intelligence, and the attraction he exerted on his colleagues.

These years determined Lüst future involvement in the European space program and opened the door to the future involvement of Europe in space science. In 1962, he becomes the President of the European Preparatory Commission for SpaceResearch(COPERS), which gave birth to the European Space Research Organization, ESRO (the ancestor of ESA), founded by Pierre Auger and Eduardo Amaldi, the fathers of CERN. 

In 1972, he became the youngest President in the history of the Max Planck Society, at a time of social and political upheaval. Nevertheless, Reimar Lüst succeeded in mastering these challenges with sustained effect. In 1984, the ESA Council, chaired by French physicist Hubert Curien, assigned him the responsibility of General Director, a position he will leave in 1990. As early as 1985, at the ESA Council of minister in Rome, he was responsible for presenting and managing the initiation of major successful decisions, which his successors and the whole European space community are still benefit from: Ariane 5, Europe’s participation to the future International Space Station, and the Horizon 2000 long-term plan which elevated ESA to the second rank of all scientific space agencies in the world. Many of the structures and instruments introduced by him during his term of office still characterize ESA to this day.

In 1990, still at ESA, he started discussions with his friend Johannes Geiss to develop an International Space Science Institute (ISSI) and convinced of the genuine value and originality of that concept, took the seminal decision to finance ISSI from ESA’s space science budget, under the conditions that the Institute should be directed by a prominent scientist of interdisciplinary international reputation, and that it should be attached to the Inter-Agency Consultative Group (IACG), which was created in 1982 to coordinate the science missions planned by ESA, USSR, Japan and NASA, to Halley’s comet at its 1986 return to perihelium. This condition is still in effect today, materialized by the presence of representatives of these four agencies in the ISSI Board of Trustees.

Between 1989 and 1999, he becomes president of the Foundation Alexander von Humboldt and under the initiative of the Bremen City, he founds the Jacobs University Bremen (IUB), which, as chairman of the board, he shaped towards excellence.

Reimar Lüst has been one of the most versatile drivers of German and European science policy. His numerous responsibilities led him to meet several heads of States and Governments. He and his wife Nina Grunenberg, Die Zeit journalist, became very close friends of Chancellor Helmut Schmidt. He was a great friend of France and was awarded by Hubert Curien the distinction of Officer de la Légion d’Honneur, one among many others such as the Order of Merit of the Federal Republic of Germany. All those who have met him during his long and extraordinary career will never forget this great scientist, great manager of big institutions, certainly very demanding and very efficient, of immense political talent, and totally faithful in his friendships.

Roger-Maurice Bonnet, International Space Science Institute

A word from the ISSI executive Director

Dear friends of ISSI,
Dear visitors of our web page,

The ISSI web page has been renovated recently thanks to Andrea Fischer and Saliba Saliba. ISSI is proud to present itself to the interested reader with a fresher look but keeping the organization of the website clearly structured and familiar so that interested users can find what they need easily and quickly.

I hope you and your loved ones are safe in this time of crisis! As many others, ISSI and its activities have been hit by the pandemic, but fortunately, no staff member has become ill. We have turned to teleworking as of March 17th and will remain so at least until the end of the eastern recess. But the ISSI office can be reached by phone and mail will be checked daily thanks to the presence of at least one ISSI staff on duty. The easiest way to reach us these days, though, is by email.

ISSI teams and workshops up to mid-May have been postponed. We will be watching the situation and adjust as it will evolve. Decisions about postponements have and will be taken together with the team leaders and the conveners at least six weeks prior to the scheduled event. As of today, there are no postponements of decisions on proposals and applications submitted to ISSI.

We all hope that the damage to the ISSI program can be kept to a minimum; we will resume as soon as the situation and the authorities will allow. ISSI will step-up its activities after the crisis to allow postponed meetings to occur as soon as possible.

In the meantime, our thoughts and sympathies are with those all over the world hit by COVID 19!

Stay safe and hope to meet you all in person at ISSI sometime soon!

Tilman Spohn

ISSI executive Director

Obituary Prof. Johannes Geiss (1926-2020)













It is with great sadness that we must bid farewell to our founding father and honorary director

Prof. Johannes Geiss (1926-2020)

Johannes Geiss died on January 30, 2020 at the advanced age of 93. In him, we have lost a great scientist and supporter of the sciences forever.

Johannes Geiss was born on September 4, 1926 in Stolp in what was then Western Pomerania as the son of an estate manager. How different the world must have looked in that time, when his grandfather had the horse hitched to the cart every two days in order to travel to the barber in the neighboring village for a shave; not fifty years later, his grandson landed an experiment on the Moon.

During the war years, Johannes Geiss was able to attend Gymnasium (high school), which he left in 1944 with a Notabitur (early school-leaving qualification in wartime) in order to immediately start a physics degree in Göttingen. Even then, his lecturers must have been struck by the young student’s rapid comprehension and irrepressible need to communication, and he was thus employed as a teaching and research assistant even during his studies. In 1950, he obtained a degree in physics from Max von Laue, and he obtained his doctorate from Wolfgang Paul in 1953. The latter he referred to, with the greatest respect, as the real part of the equally well-known but more flamboyant Wolfgang Pauli, who worked at the ETH at the time; Geiss loved such wordplays which reveal themselves to mathematical initiates.

During his time in Göttingen, Johannes Geiss also met his wife, Carmen, with whom he shared a deep partnership all his life.

His first position as a physicist brought Johannes Geiss to Fritz Houtermans’ institute at the University of Bern. Houtermans wanted to apply mass spectrometry, with which Geiss had successfully been able to determine the isotopic composition of lead, to determine the age of meteoric matter. So, at the beginning of the fifties, his glass mass spectrometer with him, he went to Bern, which would become the new center of his life, and by 1974 he was a naturalized citizen of Switzerland.

Johannes Geiss brought a breath of fresh air to an institute which was perhaps a little outdated at the time and soon found enthusiastic companions to establish a group which would quickly make a name for itself in astrophysics. Periods spent abroad in Chicago with Harold Urey and as a young professor in Miami broadened and rounded out his education; in between, he habilitated in experimental physics, in particular extraterrestrial physics, at the University of Bern in 1957. He was appointed as an associate professor in 1960, and as a full professor in 1964. At the beginning of the sixties, he had to take over management of the institute for the increasingly ill Houtermans, and was thus appointed director of the institute following Houtermans’ death in 1966; a position which he held until his retirement in 1990. In 1970/71, he also served as dean of the Faculty of Science, and in 1982/83 he served as rector of the university.

But Johannes Geiss was pulled to other places time and again in order to maintain and develop his ever-growing network. He spent the year before the first landing mission to the Moon – Apollo 11 – at NASA in Houston in order to lobby for the ingeniously simple solar wind sail developed by him and his group. The solar wind would be captured with an aluminum foil during the astronauts’ time on the surface of the Moon as the solar wind arrives there unhindered because of the Moon’s lack of an atmosphere and a magnetic field. The simplicity of the experiment and the excellent reputation of the Bernese mass spectrometer made him perfect for the job. But it took great tenacity, coupled with the previously mentioned enthusiasm and the necessary bit of luck for the sail, which weighed scarcely a pound, to fly with Apollo 11 in July 1969 and then a further four times. Its analysis, in particular the ratio of the helium isotopes captured, corresponded to a measurement of the average density of the universe as a whole – a ground-breaking result for which he, together with Hubert Reeves, was awarded the Einstein Medal by the Albert Einstein Society in Bern in 2001.

Johannes Geiss made clever use of his growing reputation in order to continue improving the conditions in Bern and to make the institute one of the top names in astrophysics and keep it that way. Under his leadership, the mass spectrometer was made so much smaller that it could be flown on space probes. At the same time, he was able to realize the necessary laboratories and a top-notch clean room in Bern for the tests and calibration. Bern thus became an internationally sought-after partner for space missions, a role which it still retains today thanks to the tireless efforts of Johannes Geiss and his successors. Of the many missions which Johannes Geiss was involved in as principal investigator or as co-investigator, the solar wind ion composition spectrometer stands out as a prime example. Developed with his friend George Gloeckler, this instrument orbited the sun on the Ulysses space probe for almost two decades on a polar orbit. This experiment achieved (among many other results) a refinement of the isotopic signature of helium measured with the solar wind sail. It is hard to find a better illustration of his progressive, unceasing spirit of research.

Even after his retirement, Johannes Geiss’ drive diminished not one jot. He still mustered all of his enthusiasm and convinced those in charge of the European Space Agency ESA and the Swiss Space Center to establish a new institute which would focus on the interdisciplinary analysis, evaluation and interpretation of the results of space missions. The International Space Science Institute was thus born almost exactly 25 years ago. In the first eight years, he served as its executive director and made the institute a center where scientists from all around the world come together in an informal and interdisciplinary setting in order to reach for new scientific horizons. Thanks to his vision, the ISSI has today become a place of meeting and exchange for thousands of space scientists.

Johannes Geiss’ work was internationally recognized with many distinguished honors. He didn’t like the often stiff atmosphere of such events, greatly preferring informal discussions with colleagues, students and anyone at all, when it came to science or any other topic which sparked his enormously broad and active interest. However, some of these honors filled him with a certain amount of pride – and deservedly so: His appointment as a Foreign Associate of the National Academy of Sciences of the USA (1978), his honorary doctorate from the University of Chicago (1986), the aforementioned Einstein Medal (2001) and the Bowie Medal, the highest honor of the American Geophysical Union (2005).

Johannes Geiss passed away in his sleep on January 30, 2020 surrounded by his loved ones. He leaves behind his wife Carmen and his daughter Jana, with her family. His legacy will continue to shine at the Physics Institute at the University of Bern and at the International Space Science Institute.

Bern, February 6, 2020
Rudolf von Steiger


Nachruf Johannes Geiss (Deutsche Version) >>

In Memoriam: Johannes Geiss  – Obituary written by Len A. Fisk and Roger-Maurice Bonnet >>

Pro ISSI Nachruf Johannes Geiss >>