“Ulysses: A New Perspective from High Latitudes“ with Rudolf von Steiger (International Space Science Institute, Bern, Switzerland)

The Ulysses mission of the European Space Agency (ESA) was launched in October 1990 with the NASA shuttle Discovery. After a close flyby of Jupiter in February 1992, it was deflected onto a unique orbit around the Sun, with its orbital plane almost perpendicular to the ecliptic plane of the planets and the solar equator. This made Ulysses the first spacecraft ever to enter the polar regions of the heliosphere and to explore them with a payload of 11 scientific instruments. Its orbital period was ~6 years; the first orbit took place in 1992-1998 during the decreasing to minimum phase of the solar activity (11-year) cycle, while the second orbit in 1998-2004 coincided with the maximum of solar cycle #23. During the third orbit, from 2004 to the end of mission in 2009, activity was again minimal, but with the solar magnetic field inverted with respect to the first orbit. So, Ulysses has actually added the third dimension to our image of the heliosphere and mapped it during an almost complete solar magnetic (22-year) cycle.

The Ulysses payload consisted of a suite of 11 instruments, which lacked an optical device for reasons that will be mentioned briefly, but was otherwise comprehensive for investigating particles and fields, and more. Among the principal results are the three-dimensional structure of the solar magnetic field together with the solar wind plasma and their evolution throughout the solar cycle. The suite also included the first ion composition spectrometer flown outside the Earth’s magnetosphere, which provided diagnostics from the solar atmosphere, comet tails, and the Universe as a whole using elemental and charge state abundances. Several instruments observed solar energetic particles, anomalous and galactic cosmic rays, and mapped their distribution at all latitudes. Other investigations observed solar radio and plasma waves, solar X-rays and cosmic gamma-ray bursts. Finally, a dust sensor and a neutral gas instrument provided first results on interstellar dust and interstellar neutral particles, harbingers from the local interstellar medium surrounding the heliosphere.

In mid-2009 Ulysses had to be switched off for reasons of diminishing power supply. Its results remain unique as no other mission is about to visit these regions of the heliosphere again soon. Only very recently two new missions, NASA’s Parker Solar Probe (launched 2018) and ESA’s Solar Orbiter (2020), are following in its footsteps. By approaching the Sun closer than any other spacecraft before, PSP has now provided evidence for the validity of a magnetic field model originally inferred from Ulysses observations. And SO is about to work its way to progressively higher latitudes using multiple Venus flybys, from where, unlike Ulysses, it will be able observe the Sun with optical instruments.

Rudolf von Steiger holds a diploma in theoretical physics (1984), a doctorate in experimental physics (1988), and a habilitation in extraterrestrial physics (1995), all from the University of Bern. He spent his postdoc years at the Universities of Maryland, Michigan, and Bern. In 1995 he joined the newly founded International Space Science Institute (ISSI) as a senior scientist. Currently he is working as a director at ISSI and also holds a professorship at the University of Bern. He is a co-investigator of the Solar Wind Ion Composition Experiment (SWICS) on Ulysses and an associated scientist of the AMPTE, ACE, and Solar Orbiter missions. He is a renowned and highly cited theoretician modelling the solar atmosphere as well as analyzing and interpreting observations of the solar wind both in the Earth’s magnetosheath and in interplanetary space.

Seminar was recorded on October 22, 2020

30 Years Hubble | 30 Ans de Hubble : Une Révolution Astronomique

Event was held on Sunday, October 25, 2020.

The Hubble Space Telescope – launched into orbit on April 24, 1990 by the Space Shuttle Discovery – is a large, space-based observatory, which has revolutionized astronomy. Far above rain clouds, light pollution, and atmospheric distortions, Hubble has a crystal-clear view of the universe. Scientists have used Hubble to observe some of the most distant stars and galaxies yet seen, as well as the planets in our solar system. On the occasion of the instrument’s 30th anniversary, La Cité des sciences et de l’industrie (located in Paris, France) is organizing a live event with Charles Bolden (NASA Astronaut), Jean-François Clervoy (ESA Astronaut), Claude Nicollier (ESA Astronaut), Kathryn Sullivan (NASA Astronaut), Daniel Kunth (Astrophysicist, IAP Paris, France), Roger-Maurice Bonnet (ESA Science Director 1983-2001), and Lucie Leboulleux (Astrophysicist, LESIA, Paris, France). This event was recorded on Sunday, October 25, 2020.


“Magnetospheric Multiscale (MMS) Mission: How Magnetic Field Lines around Earth Break and Reconnect“ with Rumi Nakamura (Space Research Institute, Austrian Academy of Sciences, Graz, Austria)

NASA’s Magnetospheric Multiscale (MMS) mission was launched in March 2015 into an elliptical orbit around Earth to study magnetic reconnection, a fundamental plasma-physical process that taps the energy stored in a magnetic field and converts it —typically explosively— into heat and kinetic energy of charged particles. MMS consists of four spacecraft with an identical set of 11 instruments made of 25 sensors that measure charged particles and electric and magnetic fields. The orbit of MMS is designed to maximize the crossings of magnetic reconnection sites.

Magnetic reconnection occurs in a narrow layer called the diffusion region where plasma particles, otherwise captured by the magnetic field, are decoupled from the magnetic field lines that are “breaking” and then “reconnecting”.  Magnetic reconnection drives eruptive solar flares, coronal mass ejections, geomagnetic storms, and magnetospheric substorms. Yet, little was known on how magnetic reconnection actually works in space inside the small diffusion region.  By separating spatial and temporal variations with a tetrahedron constellation of four spacecraft, ESA’s Cluster mission succeeded to resolve the ion-scale current sheets associated with magnetic reconnection.  With a smaller-size tetrahedron constellation and unprecedented high-time resolution instrumentation tuned for the quicker and smaller-scale electrons, MMS for the first time enabled to detect the fast processes inside the electron diffusion region.

MMS enabled to confirm some fundamental theoretical predictions, such as the current sheet geometry and gradients in electron pressure in the electron diffusion region and the reconnection rate. Yet MMS has also provided surprises, such as oscillatory localized energy conversion with unexpected intense localized electric fields. Recurrent crossings of MMS at reconnection sites showed a remarkable variety of energy dissipation and electron acceleration regions depending on parameters such as magnetic shear angle or plasma density gradient.  MMS further discovered energy conversion sites within different types of dynamic thin current sheets formed throughout near-Earth space. These include velocity induced reconnection regions within Kelvin-Helmholtz waves at the flank of the magnetosphere or turbulent current sheets in the magnetosheath and in the shock transition region, where occasionally only electrons are involved in reconnection processes.  These new discoveries from MMS stimulated new simulation/theory studies. Significant progress are made in understanding the role of non-gyrotropic electron pressure, waves and turbulence in controlling the energy conversion and the electron heating and acceleration around the reconnection site.

As a natural plasma observatory, MMS continues to obtain new knowledge on reconnection and is expected to unveil important aspects of other universal plasma processes, such as shocks and turbulence, in the upcoming years.

Dr. Rumi Nakamura is a group leader at the Space Research Institute, Austrian Academy of Sciences and a highly cited expert in magnetosphere and space plasma physics. She is the lead investigator for the Active Spacecraft Potential Control (ASPOC) on MMS mission. She is also a Co-I of Cluster, Double Star, Venus Express, THEMIS, MMS, BepiColombo and SMILE.

Seminar was recorded on October 15, 2020

A Word from the ISSI Executive Director

Dear friends of ISSI!

Dear visitors of our website!

Scientists can easily understand the instability of the situation when the coronavirus reproduction factor is about one as it has been in many countries in Europe throughout the summer. It simply says that the virus will be kept alive in the population. A slight change in the environmental parameters, e.g., a lowering of the temperature as we are entering into fall causing people to stay more inside, can cause the factor to rise and trigger exponential growth of the number of infections. Which is what we are seeing these days. Certainly, many of us had hoped that the factor would have been forced significantly below one, in which case there would have been a chance of eliminating the virus. But a society is a complicated system with many more factors – economic, political, psychological – entering into the equation and we may have found empirically that the reproduction-factor-of-one-solution at acceptably small absolute numbers was the best to be expected this summer.

In any case, ISSI has to face the fact that the COVID-19 crisis is likely going to continue for much longer than we – may be naively – had hoped and that it will impact our program even more than we had feared! We did have a successful hybrid workshop in September on the Deep Earth Interior but it appears that attendance in presence from other parts of Europe is becoming increasingly impractical and has become impractical for many. Visitors to ISSI from a growing number of countries will have to go into quarantine for 10 days should they come to Bern and it is not unlikely that they may have to go in quarantine in their own country when they come home after the event. The borders in Europe are open, but it is not very reasonable and practical to travel! This observation is the reason why teams and workshop conveners are continuing to shift their meetings to later.   

 At ISSI, we are exploring even more what the world wide web has to offer to help us through the crisis. Since August, we are having a weekly online seminar series on missions that have changed the game in the space sciences. This “Game Changers” seminar series (Thursdays at 5pm CEST) has started with seven talks on planetary exploration missions and has now turned to heliosphere and plasma missions and will turn to astronomy and astrophysics missions in November and December. The talks have all been recorded and are available for view on our website. Attendance to the seminars varied between 150 and 265 and download figures peeked at more than 1600. We have planned the seminar until the end of the year for now, but we will see what we will have to follow-on next year. In addition, we are brainstorming with the community on how we can improve the working situation for the active International Teams and the planned Workshops, Working Groups and Forums. Some of the ideas and online solutions will be tried in the coming months and hopefully, some will even have the potential to be useful when the crisis will finally be over.

Finally, let me turn to our 25th anniversary that has received not as much attention as it would have in more normal times: ISSI turned 25, already in January! Unfortunately, we mourned the passing of Johannes Geiss, the institute’s founding father, that month. We had made plans in late 2019 how to celebrate but these needed first to be postponed and have now become largely unfeasible. But, we have a little birthday present upcoming for the community!

Stay tuned and stay healthy and our thoughts continue to be with those severely hit by the pandemic

All the best

Tilman Spohn

ISSI executive director

“Dawn to Vesta and Ceres“ with Carol Raymond (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA)

What is the nature of the asteroid belt? Is it a failed planet or a remnant belt-like structure from the times of the formation of the solar system? What are the properties of its major bodies and how did they evolve? Do the bodies retain a record of the chemical gradients of the protoplanetary disk? Those were questions that the NASA Dawn mission was set to answer when it was launched in September 2007 to the two largest bodies in the main asteroid belt between Mars and Jupiter, protoplanet Vesta and dwarf planet Ceres. The mission, equipped with a framing camera, a visible and infrared spectrometer and a g-ray and neutron detector, achieved a number of firsts during its lifetime. It was the first mission to orbit an object in the main asteroid belt, the first to orbit two extraterrestrial destinations, and the first to orbit a dwarf planet, a class of planets the IAU had introduced in 2006, with Pluto being the most prominent member. The spacecraft arrived at Vesta, the smaller of the two in July 2011 and orbited the asteroid for 14 months before it left for Ceres where it arrived in March 2015. The spacecraft exhausted all the available hydrazine fuel two years ago in October 2018 and went silent, but is still in orbit around the dwarf planet. The spacecraft used ion propulsion to reach its destinations in the asteroid belt and for all orbit transfers at the bodies.

Dawn confirmed that Vesta is the source of a particular class of meteorites, the HED (howardite-eucrite-diogenite) meteorites that comprise about 6% of all meteorites found to date. The meteorites most likely escaped from Vesta when large impacts created two major basins of several hundred kilometers diameter near the asteroid’s south pole, which also resulted in a trough system circling near the equator.  By mapping Vesta’s gravity field, the mission further showed that the asteroid was consistent with a differentiated rocky body with a dense iron-rich core, and the images showed that it had a complex geological history.   Generalizing the findings at Vesta, it is thought that early-forming planetesimals could have been differentiated before they were accreted onto proto-planets.  Deposits of hydrated minerals discovered on Vesta’s surface provided evidence that water-and carbon-rich planetesimals delivered volatiles to Vesta, and likely were a major source of volatile delivery to the growing terrestrial planets.

Orbiting at a larger distance to the sun, and about twice as large, Ceres was found to be quite different from Vesta with an ice-rich surface and evidence for a subsurface ocean, at least in the past. The distribution of bright deposits on its surface suggest that Ceres is active or was most recently so. The bright material is identified as deposits of mostly sodium carbonate that came from liquid percolating up from subsurface brines. Even organics were identified on its surface. Judging from the cratering record, Ceres’ surface is varied in age. Ammonia found on Ceres suggests that the dwarf planet may have originally formed at a larger orbital distance and was later transferred further in by a large-scale orbital instability as has been suggested by some models of solar system formation. 

Dr. Carol Raymond Carol is a principal scientist at the Jet Propulsion Laboratory of the California Institute of Technology. She was the Deputy Principal investigator for the Dawn mission and became the Principal Investigator during the extended mission. She is a member of the Europa Clipper Magnetometer team and a Co-I on the NASA Psyche mission. Carol Raymond started her career studying terrestrial paleomagnetism and became focused on planetary science when the magnetized crust of Mars was discovered. She is a highly cited and renowned planetary physicist with a wide-range of interests.

Seminar was recorded on October 8, 2020

Job Posting: Secretary (100%)

The International Space Science Institute (ISSI) is an Institute of Advanced Studies where scientists from all over the world meet in a multi- and interdisciplinary setting to reach out for new scientific horizons.

To support these activities, ISSI is seeking a

Secretary (100%)

to begin as soon as possible or as agreed.

Duties include:

  • Secretarial tasks, including mailings and maintenance of mailing lists
  • Hotel and travel arrangements both for visiting scientists and staff
  • Checking and classification of invoices
  • Preparation of meetings / documentation, writing minutes
  • Correspondence in German / English / (French)

We’re looking for someone who is:

  • Native German speaker with excellent spoken and written English; good French is a plus
  • Skilled in MS Word, Internet and team collaboration tools; knowledge of other programs, especially Access, Powerpoint and Excel, is a plus
  • Willing to work in a small team, but
  • Able to work independently
  • Willing to assist other staff members in administrative matters as needed

We offer:

  • An interesting, challenging international atmosphere
  • A small organization with 15 members
  • Salary commensurate with experience
  • Employment conditions similar to the University of Bern

Job application and usual documents (in German or English) should be sent as a pdf-file by e-mail to silvia.wenger@issibern.ch         

“The Sun from SOHO, and First Glimpses of Parker Solar Probe and Solar Orbiter“ with Daniel Müller (Solar Orbiter Project Scientist, ESA – ESTEC, The Netherlands)

SOHO, the Solar and Heliospheric Observatory, is a cooperative project of ESA and NASA to study the Sun, from its deep core to the outer corona, the solar wind, and energetic particles. Together with Cluster it forms the Solar-Terrestrial Science Programme (STSP), the first cornerstone of ESA’s long-term science program “Horizon 2000.” SOHO was launched on 2 December 1995 and inserted into a halo orbit around the L1 Lagrangian point in February 1996. The twelve instruments on SOHO have provided an unparalleled breadth and depth of information about the Sun, from its interior, through the hot and dynamic atmosphere, out to the solar wind and its interaction with the interstellar medium. SOHO’s findings have been documented in over 5900 scientific publications in the refereed literature, authored by more than 4000 scientists worldwide. SOHO provided the first images of structures and flows below the Sun’s surface and of activity on the far side of the Sun. It discovered sunquakes and has shed new light on a number of structural and dynamic phenomena in the solar interior, such as the absence of differential rotation in the radiative zone, subsurface zonal and meridional flows, sub-convection zone mixing, and very slow polar rotation. It provided evidence for upward transfer of magnetic energy from the surface to the corona through a “magnetic carpet” and revealed an extremely dynamic solar atmosphere where plasma flows play an important role. It discovered new dynamic phenomena such as coronal waves, measured the acceleration profiles of the slow and fast solar wind, and identified the source regions and acceleration mechanisms of the latter. It revolutionized our understanding of solar-terrestrial relations and dramatically boosted space weather forecasting capabilities by providing, in a near-continuous stream, a comprehensive suite of images covering the dynamic atmosphere and extended corona. SOHO observed and characterized over 40,000 coronal mass ejections and, as a byproduct, became the most prolific discoverer of comets in astronomical history, with over 4000 comets found in SOHO observations, most of them by citizen scientists accessing SOHO real-time data via the Internet.

Control of the spacecraft was lost in June 1998 due to an unfortunate series of events during a spacecraft maneuver, but restored three months later in a dramatic recovery operation. Miraculously, all twelve instruments were still usable, most with no ill effects, despite the enormous temperatures they were exposed to during the time contact with SOHO was lost. Despite subsequent failures of all three gyroscopes (the last in December 1998), new gyroless control software installed by February 1999 allowed the spacecraft to return to full scientific operations. This made SOHO the first three-axis stabilized spacecraft operated without gyroscopes.

While SOHO is still operating today with 7 of its 12 instruments at almost full capability, two new solar missions have joined it recently. In 2018 the Parker Solar Probe was launched by NASA and already has approached the Sun closer than any spacecraft before. In February 2020 ESA launched its Solar Orbiter that will approach the Sun to as close as 0.28 AU and will use a series of Venus fly-bys to work its way to higher and higher latitudes, thus obtaining an unprecedented view onto the solar polar regions. The future game changers are underway, but they stand on the shoulders of a giant – SOHO.

Dr. Daniel Müller holds a Ph.D. in Physics from the Albert-Ludwigs-Universität Freiburg, Germany. After a Marie Curie Fellowship at the University of Oslo, Norway, he joined ESA’s SOHO team at NASA’s Goddard Space Flight Center, where he became Deputy Project Scientist of SOHO. In 2010, he moved to ESTEC to start working on Solar Orbiter, and has been serving as the mission’s Project Scientist since 2012. In addition to his scientific and project management work, he has a strong interest in high-performance scientific data visualization. In particular, he is coordinating the development of the open-source Helioviewer software and is the ESA Lead of the ESA/NASA Helioviewer Project.

This seminar was recorded on October 1, 2020

Interview with Johannes Geiss Fellow Bruno Leibundgut

Bruno Leibundgut (European Southern Observatory (ESO), Garching, Germany) was elected as the Johannes Geiss Fellow 2019. He will give a Pro ISSI Talk on “Cosmology Today”, October 14, 18:15h CET. You can join this talk online (Zoom Webinar): https://bit.ly/2DJ74Pr  Meeting ID: 81330166057 Password: 481628. More Information about the Pro ISSI Talk >>

In the following paragraphs he answers a few questions – asked by Lorena Moreira, ISSI Earth Sciences Post Doc – about his scientific work (in pandemic times).

Lorena Moreira: How has the Johannes Geiss Fellowship contributed to your career? And why did you apply to the Fellowship?

Bruno Leibundgut: The Johannes Geiss Fellowship was a great opportunity for me to refocus some of my research and reconnect to Swiss astronomy. Most of my professional career was spent at an international organisation and an observatory. This means that I had to deal with many science administration aspects and for a while, during my time as ESO Director for Science, was contributing to the scientific direction of the organisation and managing the scientific environment. There was not much time left for research. 
The Johannes Geiss Fellowship allowed me to catch up with recent developments in my fields of supernova physics and cosmology. Being able to devote all of my time to research was a very welcome change to my current work. This was also the reason to apply for the Johannes Geiss Fellowship. It seemed to be an ideal opportunity to combine the research time it promised at a scientific institute in Switzerland. I used the time to meet several astronomers in Bern and Geneva to discuss various projects and the interaction of Swiss astronomers with ESO.

Bruno Leibundgut, Johannes Geiss Fellow 2019, and Lorena Moreira, ISSI Post Doc in Earth Sciences. This picture was taken in January 2020  (before the lockdown).


Lorena Moreira: On which projects did you work during your stay at ISSI?

Bruno Leibundgut: The original plan was to write up a paper from a Masters thesis of one of my students on SN1987A. He analysed the evolution of this nearest supernova in several centuries from a decade of HST observations and his results should be cast into a publication. My first weeks at ISSI were used to clear my ESO work backlog. I also had a couple of trips to conferences and for talks during my Johannes Geiss Fellowship. My research at ISSI focussed is on some cosmology aspects, which I wanted to explore more deeply. This also involved learning new software tools. The time at ISSI enabled me to enlarge my knowledge and read up on topics, which in my normal work life always seemed to fall to the wayside. 
The main research work in the end was on the adH0cc (accurate distances for H0 through core collapse supernovae) project. I am leading a large programme with the ESO Very Large Telescope (VLT) to carefully observe about 2 dozen individual Type II supernovae to determine their distances and then derive the local cosmic expansion rate, the Hubble constant. We acquire detailed spectroscopy and photometry of a supernova over several weeks to follow its brightness evolution and the speed with which it expands to connect these parameters into a distance measurement. Much of the data reduction processes were worked out during my time in Bern.

Lorena Moreira: What are according to you the next breakthroughs in cosmology? What do you think the future hold for your scientific career?

Bruno Leibundgut: There is a discrepancy of the value of the Hubble constant from measurements in the local and the distant universe. This ‘Hubble tension’ could, if confirmed, point to deficiencies in the currently favoured cosmological model, the Lambda Cold Dark Matter (Lambda CDM) universe. This model contains several components that at the moment lack a physical understanding, namely ‘dark energy’ in the form of Einstein’s cosmological constant Lambda and ‘dark matter’, which is inferred indirectly, but has so far not been detected as a particle. These particles would have to be fairly massive so that they can clump under gravity to form galaxies. We call this type of matter ‘cold’. The difference of the Hubble constant as calculated from the information in the distant universe, the measurements from the cosmic microwave background as determined by the ESA Planck satellite, and the direct measurement in the local universe shows that the Lambda CDM model may not be complete. Right now it is unclear, whether this is a real physical effect or just systematic problems of the Hubble constant determinations. It is important to explore as many independent methods as possible to check that we are not fooled by unknown problems in the measurements. 
Our adH0cc project contributes a new method of the local Hubble constant that is completely independent of any of the other determinations. It will take a couple of years until we have collected the necessary data and can analyse them. In the end, we should be able to check for any systematic effects we use to measure the Hubble constant. In some sense, this work arches back to the start of my scientific career, where I also tried to determine the Hubble constant – with an uncertainty that was a factor 10 higher than today’s measurements! 
I was always interested in the physics of stellar explosions and how this connects to their use as cosmological distance indicators. My research of this connection continues and I hope that I can learn about the explosion physics as much as about cosmology. There are plenty of unsolved problems in both areas. The current cosmological picture has firmed up significantly over the past two decades, but with dark energy and dark matter contains at least two parameters, which lack a physical understanding. 

Lorena Moreira: As you have recently experienced staying away from your permanent office during your visits at ISSI and during the current pandemic situation, what do you think that we can learn from these experiences to thrive scientifically?

Bruno Leibundgut: ISSI was a great place for me to focus on my research. The quiet environment allowed me to concentrate on the adH0cc project and make the necessary preparations to fully explore the data. Such quiet periods, when the hectic of the outside world is shielded, are important in a research career. I believe, they are needed to focus one’s mind. Small ’sabbatical’ stays, like my Johannes Geiss Fellowship at ISSI, are important to reflect on the research direction. The ISSI setting was especially joyful for me; I could quietly sit in my office and work for myself but was connected to the scientific environment of the institute and the University of Bern. I participated in the CSH Science and Religion Forum: “Limits of Science – Opportunities for Religion?”, which I would not have been able to do in my regular work environment, simply because there would not have been the time. The combination of ‘quiet time’ in a lively environment seems to me conducive – maybe even central – to research work. The exchange beyond the limited scientific topics to enlarge the intellectual horizons is key for good science.  
With the pandemic and increased home office the nature of meetings has changed. The many online meetings and conferences offer new opportunities, e.g. participation from different time zones and recording of presentations for asynchronous viewing. We experience an increased participation through the online format, which means that more people can attend online meetings and at a decreased cost. My experience, though, is that discussions are stifled through the online format and are much reduced. 

The future will see a combination of the different formats. Small focussed meetings to discuss specifics and with free-format discussion rounds profit from direct and extended interaction, while the general information exchange meetings should become hybrids with some physical participation and streaming/recording for a wider audience.  


The Johannes Geiss Fellowship (JGF) is established to attract to ISSI – for limited duration visits – international scientists of stature, who can make demonstrable contributions to the ISSI mission and increase ISSI’s stature by their presence and by doing so will honor Johannes Geiss for his founding of ISSI and his contributions to ISSI, and for his many contributions to a broad range of space science disciplines.

In 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. Read here the Interview with Weiqing Han and Sabine Schindler – Johannes Geiss Fellows 2020 >>




“Rosetta at Comet Nucleus 67P/Churyumov-Gerasimenko” with Jessica Agarwal (TU Braunschweig, Germany)

The ESA Cornerstone mission Rosetta was off to a difficult start after the launch had to be postponed and the target comet 46P/Wirtanen replaced in 2003 by 67P/Churyumov-Gerasimenko. Finally launched in April 2004 and after a ten years journey, the Rosetta space craft went into orbit around the nucleus in August 2014, carrying a suite of instruments and the Philae lander. Philae landed on November 12th – not quite at the foreseen sunlit location but on its side and in the shadow of a cliff. It transmitted data for roughly 60 hours until the power of its primary battery had been spent. The lander was located and its flight above the nucleus surface reconstructed using data from its magnetometer and it was finally “found” in images taken by the OSIRIS camera on board the orbiter. The mission ended in 2016 after the Rosetta orbiter spacecraft was crash-landed on the nucleus taking images and other data up to the very end. 

Rosetta had been named after the Rosetta stone because the data would be used to decipher the formation of the solar system just as the Rosetta stone was the clue to decipher the Egyptian hieroglyphs. The Philae lander – in turn – was named after the Philae obelisk that has a bilingual inscription in Greek and Egyptian hieroglyphs that complemented the information from the Rosetta stone.

Rosetta carried a substantial suite of instruments on the orbiter and the lander, many complementary and some with elements on both such as the CONSERT radar system that allowed part of the nucleus interior to be screened. Cameras and spectrometers covered the electromagnetic spectrum from ultraviolet to mm-wavelengths and mass spectrometers explored the composition of the cometary dust and ice. A radio science experiment helped determine the mass and the porosity of the nucleus. Rosetta was also equipped with several dust detectors and magnetometers.

The mission proved to be a masterpiece in space technology and operations – the latter in particular because of the sophisticated maneuvers to accelerate the spacecraft through a number of gravity assists to its target and because of the approach to a largely unknown, outgassing small body with an irregular gravity field, orbit insertion and finally landing. Its results put many new constraints to models of the origin and evolution of comets as well as models of the formation of the solar system. For instance, it was shown that the chemistry of the nucleus was highly complex with manifolds of organic compounds. Amongst the most surprising findings was the existence of molecular oxygen that suggested that the nucleus formed very early and was kept at very low temperatures for much of its existence until its orbit was disturbed and ended in the Jupiter family. Other findings concerned the extremely high porosity of the nucleus of roughly 70% and its variability of strengths at various scales, and the diversity of processes connected to the erosion of the surface. Although a large number of publications appeared in the first years after the mission ended – including an ISSI book also published online in Space Science Reviews – the scientific harvest will likely continue for decades. 

Prof. Jessica Agarwal is since May 2020 Lichtenberg professor at the TU Braunschweig in Germany. She was at the Max-Planck Institute for Solar System Research before where she was a member of the OSIRIS team. Jessica Agarwal specializes in the physics of active bodies, both comets and asteroids and has discovered the first active binary asteroid in 2016 using the Hubble Space telescope. She is a highly cited and renowned expert of active small bodies in the solar system. 

Seminar was recorded on September 24, 2020.