“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

“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

“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

“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.

 

“Cassini-Huygens at Titan” with Athena Coustenis (Paris Observatory, CNRS, PSL Univ., Sorbonne Univ., Univ. Paris, France)

The NASA/ESA/ASI Flagship-class Cassini-Huygens mission was launched on October 15, 1997 and entered into orbit around Saturn in July 2004. It carried the Huygens probe which was the first ESA planetary lander and landed on Titan on January 14, 2005. The lander transmitted data for 90 minutes during descent and after landing. The mission was an outstanding success. Most of what we know today about Saturn, its largest moon Titan and the Saturn system of rings and satellites comes from this mission which was named after Giovanni Cassini and Christiaan Huygens who discovered main features of the ring system and several satellites, including Titan.

The Cassini orbiter carried a large suite of instruments including optical and mass spectrometers, an imaging system, as well as a magnetometer, a cosmic dust analyzer and other fields, particles and waves and microwave remote sensing instruments. The Huygens probe had an atmospheric structure instrument, a doppler wind experiment, a descent imager and spectral radiometer, a gas chromatograph mass spectrometer, an aerosol collector and pyrolyser, and a surface science package.  The objectives of the mission included the exploration of the planet, its atmosphere and magnetosphere, and its moons as well as the prominent ring system. For Titan, the objectives included the study of the atmosphere, the properties of the surface and the interior. What we knew about Titan before Cassini-Huygens came from the Voyager missions in the 80s from one fly-by, but the Cassini-Huygens large number of close fly-bys and the in-situ exploration revolutionized our understanding of the satellite.   

Titan is the only moon in the solar system that has a substantial and optically thick atmosphere dominated by dinitrogen (N2) with traces of methane and hydrogen leading to an evolved organic chemistry, but very little oxygen and low temperatures of about -180°C. Instead of water, methane is at the center of a methanological cycle (a weather system in which methane takes the role of water) creating features like haze, precipitation, lakes and rivers or drainage systems of liquid hydrocarbons on Titan. Evidence was also found for the presence of an undersurface liquid water ocean on Titan, similar to Enceladus, as revealed by Cassini gravity data. Thus, the atmosphere and surface on Titan are similar to the Earth’s but different at the same time in terms of materials, creating the opportunity to study a unique world with a strong astrobiological potential.

The mission ended almost three years to the date of the present seminar on September 15th, 2017, when the Cassini spacecraft plunged and disintegrated in Saturn’s atmosphere sending more valuable data to the end. In addition to the exploration of Titan, which was a major target, another highlight of the mission was the discovery of active cryovolcanism on Enceladus, a satellite of only roughly 500km diameter, spurting water vapor geysers to space.  

Prof. Athena Coustenis is director of research at the Laboratoire d’etudes spatiales and d’instrumentation en astrophysique (LESIA) at the Paris Observatory, in Meudon, France. She is involved in several NASA and ESA space missions and has served on a large number of advisory and managing committees for the agencies, COSPAR, the IAU, ISSI, IUGG, EGU, DPS and EPSC. Athena Coustenis is a highly cited and respected expert for the planets and moons of the outer solar system, and in particular, for Titan.

This seminar was recorded on September 17, 2020.

“Venus Express” with Ann C. Vandaele (Belgian Institute for Space Aeronomy, Belgium)

Venus Express – VEX for short – launched in 2005 was the first and up to now only ESA mission to explore the planet. Venus, our inner neighboring planet is relatively little explored as compared with Mars. This is due to the forbidding temperatures on the surface – about 450°C – and its corrosive, optically thick atmosphere. The latter prohibits exploration of the surface with standard cameras and motivates the use of radar and infrared mapping. Venus is close to the Earth in terms of mass and radius but its atmosphere likely underwent runaway greenhouse heating that removed any water that may have been on the surface in its early days. Venus orbits closer to the Sun which explains part of the heating and its atmosphere – much more massive than Earth’s – is dominated by carbon dioxide, an effective greenhouse gas. Planetary scientists also wonder about the lack of a magnetic field and its tectonic evolution and whether it ever had anything like Earth’s plate tectonics. VEX has been orbiting and exploring the planet for a decade before it was commanded to dive into the atmosphere where it burned taking measurements until the end in early 2015.

VEX profited substantially from hardware developments for Mars Express and Rosetta, also for its suite of instruments. It was equipped with a plasma and energetic particles analyzer, a magnetometer, spectrometers for the ultraviolet, visible and infrared parts of the electromagnetic spectrum, a radio science package and a monitoring camera. Venus Express for the first time observed the south polar region on the night side of the planet and discovered atmosphere vortices that circle the pole. In particular its mapping infrared spectrometer detected anomalies in the thermal surface emission which might be proof of  recent volcanic activity. An ozone layer was discovered by the ultra-violet spectrometer. Venus Express has motivated scientists to propose follow-up missions, three of which are under consideration by ESA and NASA. 

Dr. Ann Carine Vandaele is the head of the Planetary Aeronomy Group at the Royal Belgian Institute for Space Aeronomy and the Principal Investigator of the SOIR infrared spectrometer, a part of the SPICAV package of spectrometers on the mission. Ann C. Vandaele is a civil engineer and a physicist by training and has been involved in Earth observation as well as the spectroscopic study of Mars and Venus. She is a highly cited expert of planetary spectroscopy.

This Seminar was recorded on August 27, 2020

“Mars Express” with Ralf Jaumann (Freie Universität Berlin, Germany)

Mars Express – MEX for short – launched in 2003 was the first ESA mission to explore a planet. It was followed by Venus Express (VEX) launched in 2005. The Express missions and the Rosetta mission to comet Churyumov-Gerasimenko launched in 2004 use the same space craft bus. After some early problems including the loss of the Beagle II lander, MEX has been orbiting and exploring Mars for almost two decades. The mission is intended to be extended until end of 2022.

MEX is equipped with instruments from Germany, France, Italy and Sweden.  The High Resolution Stereo Camera HRSC maps the three-dimensional geomorphology of the surface and provides geological context for mineralogical spectrometer observations and subsurface structure sounding by radar.  In addition, the atmospheric circulation, and the interaction of the atmosphere with the interplanetary medium are observed by specific instruments. The HRSC still is the only stereo camera on orbit around Mars. Together with data from the Mars Observer Laser Altimeter it allowed a topographical mapping of the surface with unprecedented accuracy and resolution, and is still used not only for Mars geology work but for lander and rover mission planning. Among the many achievements of the mission are the detection of water ice at its poles with a possible water layer at depth underneath the south pole, the water related mineralogical evolution of the Martian surface from volcanic rocks weathered to phyllosilicates followed by sulfate rich deposits, ancient water surface and subsurface circulation and precipitation rates over time, methane in the atmosphere, a new Martian stratigraphy and a detailed dating through crater statistics of surface units. Mars Express has in many aspects revolutionized our understanding of the planet and has motivated follow-up missions such as ESA’s Trace Gas Orbiter.

Prof. Ralf Jaumann is a professor at the Free University of Berlin and has served until 2019 as deputy director of the DLR Institute of Planetary Research. He is principal investigator of the HRSC on the mission.Ralf Jaumann is a highly cited expert in Mars and lunar science. In addition to his work for MEX, he has built and scientifically used cameras for DAWN and Mascot on Hayabusa2. He has been a Co-I or science team member on Cassini, Rosetta, Venus Express, and InSight.

This Seminar was recorded on August 20, 2020

 

 

“The New Horizons Mission to Pluto and the Outer Solar System” with Alan Stern (SWRI Boulder, USA)

The New Horizons mission – a NASA New Frontiers class mission – was launched early 2006 and was the first to explore the Pluto-Charon binary planet and its satellites, up-close through a six-month long fly-by in 2015. After leaving the Pluto-Charon system, the spacecraft went on to make the first spacecraft exploration of Kuiper belt objects (KBOs). It was eventually targeted to fly-by 486958 Arrokoth (originally nicknamed Ultima Thule) in 2019. The spacecraft is one of only five to have achieved escape velocity from the Solar System. It is possible that the spacecraft will fly by another KBO still to be detected on its way out of the solar system.  

Equipped with a suite of visible, infrared, and ultraviolet remote sensing instruments and plasma and energetic particle spectrometers, as well as a dust impact detector, New Horizons gathered data that revolutionized our understanding of the Pluto-Charon system and Kuiper belt objects. To name a few discoveries, Pluto was found to have actively flowing glaciers covered with nitrogen ice that even control its climate. Pluto is tectonically and volcanically active with icy slush “lava” having poured onto the surface, likely controlled by processes in a subsurface ocean. Even Charon’s surface shows traces of cryo-volcanic activity. Being so far out in the cold reaches of the Solar System, the Pluto-Charon system is a remarkably active world!

Dr. Alan Stern is a researcher at the Southwest Research Institute in Boulder, Colorado and the Chief Scientist of World View, a commercial high-altitude ballooning company. Alan serves as the principal investigator of the New Horizons mission and the lead of the science team. World View https://worldview.space/ has bases in Arizona and Australia, flies payloads for astronomy, planetary astronomy, solar physics, earth observations, and atmospheric studies, and is actively reaching out to connect with scientist interested in flying payload all over the world. To sign up for World View’s research mailing list, go to https://world-view-research-education.mailchimpsites.com/.

This Seminar was recorded on August 13, 2020

“The Hayabusa Missions” with Seiji Sugita, University of Tokyo, Japan

The Hayabusa missions have been the first landing and sample return missions to asteroids. They are marveled worldwide amongst space scientists, engineers and enthusiasts for the novel technologies used at comparatively low cost. Hayabusa was launched in 2003 to the near-Earth asteroid Itokawa and returned asteroid dust to the Earth, when the sample container landed in Australia on June 13, 2010. This was the first sample of an asteroid (S-type) brought back to Earth. Hayabusa was followed by Hayabusa2 launched in 2014 to C-type near-earth asteroid Ryugu. Hayabusa2 took samples from two sites in February and July 2019 that are expected back on December 6, 2020. In addition to sampling, Hayabusa2 carries an ambitious payload including optical and thermal infrared cameras, a near-infrared spectrometer and a LIDAR. Moreover, Hayabusa2 created an impact crater on Ryugu with its small carry-on impactor (SCI) and landed four rovers, one, MASCOT, provided by the German Aerospace Center DLR and three Japanese Minerva rovers. With its payload, Hayabusa2 did a thorough exploration of a very primitive body, a likely remnant of the planetesimals that formed the Earth and the planets.

Dr. Seiji Sugita is a professor at the Department of Earth and Planetary Science at the University of Tokyo and the Science PI of the Hayabusa2 Optical Navigation Camera. His general interest is in the origin and evolution of planets and their surface environments including life. He specializes in impact experiments, high-speed optical spectroscopy and mass spectroscopy.

This Seminar was recorded on July 30, 2020