“The Hubble Space Telescope: From Cosmological Conflict to Alien Atmospheres“ with Tom Brown (Space Telescope Science Institute, Baltimore, USA)

The Hubble Space Telescope is one of the most successful scientific experiments in history. The observatory is an international project pursued as a collaboration between the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). Launched in 1990 into low Earth orbit, Hubble was continuously improved through a series of five servicing missions, and we expect to continue science operations well into the 2020s. Hubble’s four active science instruments provide unique and powerful capabilities for imaging, spectroscopy, and astrometry at ultraviolet, optical, and near-infrared wavelengths, enabling discoveries in a wide range of science, but also extending discoveries from other facilities on the ground and in space. The ultraviolet capabilities are in particularly high demand; critical diagnostics of temperature and chemistry fall at these wavelengths and are inaccessible below the Earth’s atmosphere.

Hubble science evolves with the field. At the time of launch, there were no known exoplanets, but Hubble is currently the premier facility for characterising exoplanet atmospheres, with a significant investment of observing time each year. It has also found dusty disks and stellar nurseries throughout the Milky Way that may one day become fully fledged planetary systems.  Characterising the expansion of the universe was always a key project of the mission, but Hubble played a critical role in the discovery of the accelerating expansion associated with the mysterious dark energy permeating the universe, and recent measurements made in tandem with Gaia are creating a tension in cosmology that may be revealing new physics. Hubble demonstrates the ubiquity of black holes in the universe, provides insight into galaxy mergers and evolution over cosmic time, and probes star formation on a variety of distance scales.  Closer to home, Hubble has tracked interstellar objects as they soared through our Solar System, watched a comet collide with Jupiter, discovered moons around Pluto, and complemented other space missions dedicated to planetary science. Hubble’s focus will evolve further in the coming decade of all-sky surveys and multi-messenger astronomy. Some of Hubble’s most exciting results will be highlighted as well as expectations for the 2020s.

Hubble orbits 340 miles above Earth’s surface. This vantage point allows Hubble to observe astronomical objects and phenomena more consistently and with better detail than generally attainable from ground-based observatories. Named in honour of the trailblazing astronomer Edwin Hubble, the Hubble Space Telescope has revolutionised astronomy since its launch and deployment by the space shuttle Discovery in 1990.  Hubble has made more than 1.4 million observations over the course of its lifetime. Over 17,000 peer-reviewed science papers have been published on its discoveries. These papers have been referenced in other publications approximately 900,000 times, with the past year breaking a new yearly record of 1000 refereed papers. Every current astronomy textbook includes contributions from the observatory, and 1 in 6 astronomical research papers are influenced by Hubble. Hubble’s discoveries continue to fascinate the public, and images of the telescope, servicing missions, and science results have become cultural icons.  They appear regularly on book covers, music albums, clothing, TV shows, movies, and even ecclesiastical stained-glass windows.

 

Tom Brown is the Hubble Mission Head at the Space Telescope Science Institute, the Science Operations Center for the Hubble Space Telescope.  He attended the Pennsylvania State University (B.S., majors in physics and astrophysics) and the Johns Hopkins University (M.A. and Ph.D., astrophysics).  He has previously worked with the Astro-2 Space Shuttle mission, two Hubble instruments, and the James Webb Space Telescope.  His research focuses on galaxy formation and stellar evolution.  His recent research highlights include evidence that reionization quenched the star formation in nearby dwarf galaxies, and measurement of the first precise parallax for an ancient star cluster.

 

Seminar was recorded on November 19, 2020

“The Earth, a Planet like no Other” – Online Presentation with Anny Cazenave

This presentation was recorded on November 13, 2020 (on the occasion of ISSI’s 25th anniversary).

Abstract: The Earth is the only planet of the Solar System hosting evolved life. «How to build an habitable planet ?» has led to considerable scientific literature in the recent decades and has strongly motivated research on exoplanets. All along its history the Earth has displayed specific chemical and physical properties, including a relatively stable climate that a played major role in the evolution of living organisms. In this presentation we discuss the physical particularities of planet Earth, such as gravity and magnetic fields, rotation, mantle convection and plate tectonics, volcanism and water cycle, and their impacts on climates and life, from paleo times to present. Today, Homo Sapiens polulation is approaching 8 billions, a factor 8 times larger than 2 centuries ago, and an indirect consequence of fossil energy use and associated technological innovation. However, our present-day world is facing a number of new «Grand Challenges», as summarized by the United Nations (UN) 2030 Agenda for Sustainable Development. By providing invaluable information on the Earth system and its evolution under natural and anthropogenic forcing factors, Earth observation from space has a key role to play for reaching several of the 17 Sustainable Development Goals of the UN 2030 Agenda, in particular those related to current climate change, water resources, land and marine biodiversity and food security.

Anny Cazenave received her Ph.D. in geophysics in 1975 from the University of Toulouse. Subsequently, working at the French space agency CNES, she went into space geodesy, the use of satellites to track changes in Earth’s surface, gravity field and orientation in space. She first focused on the dynamics of the oceanic crust and the mechanically strong layer of the uppermost mantle below it. Among other things, she used early space- borne radars to show that the ocean surface is not flat, but follows the topography of the ocean floor. In other early work, she addressed questions about the rotation of Venus and the origins of the Mars moons, Phobos and Deimos. Towards the end of last century, European and American space agencies launched a new series of satellite radar altimeters capable of monitoring sea level everywhere in the world oceans in more or less real time. By the early part of the 21st century, it had been determined that global sea level was rising by at least about three millimetres a year. As one of the leading scientists in the joint French/American satellite altimetry missions, TOPEX/Poseidon, Jason-1, and the Ocean Surface Topography Mission, Anny Cazenave has contributed to a greater understanding of this sea level rise and its dependence on global warming. Besides a large number of publications, Anny was lead author of the sea level sections of the Intergovernmental Panel on Climate Change’s most recent full reports, in 2007 and 2014.

Since 2013, she has been director of Earth sciences at the International Space Science Institute in Bern. In 2020, she received the prestigious Vetlesen Prize, often referred to as the Nobel Prize in geophysics, for her pioneering work in using satellite data to chart and quantify rises in the surface of the oceans, and related changes in ice sheets, landmasses and freshwater bodies.

 

“Gaia – The Dynamic Sky in 3D“ with Anthony Brown (Leiden Observatory, Leiden, The Netherlands)

The talk will consist of an overview of the Gaia mission and how it maps the Milky Way in 3D. This is followed by scientific highlights from the second Gaia data release, which took place in April 2018 and has resulted in over 3500 peer-reviewed publications to date. 

Gaia is global space astrometry mission, it will make the largest, most precise three-dimensional map of our Galaxy by surveying more than one billion stars. Gaia will monitor each of its target stars about 70 times over a five-year period. It will precisely chart their positions, distances, movements, and changes in brightness. It is expected to discover hundreds of thousands of new celestial objects, such as extra-solar planets and brown dwarfs, and observe hundreds of thousands of asteroids within our own Solar System. The mission will also study about 500 000 distant quasars and will provide stringent new tests of Einstein’s General Theory of Relativity.

Gaia will create an extraordinarily precise three-dimensional map of more than a billion stars throughout our Galaxy and beyond, mapping their motions, luminosities, temperatures and compositions. This huge stellar census will provide the data needed to tackle an enormous range of important problems related to the origin, structure and evolutionary history of our Galaxy.

For example, Gaia will identify which stars are relics from smaller galaxies long ago ‘swallowed’ by the Milky Way. By watching for the large-scale motion of stars in our Galaxy, it will also probe the distribution of dark matter, the invisible substance thought to hold our Galaxy together.

Gaia will achieve its goals by repeatedly measuring the positions of all objects down to 20th magnitude. For all objects brighter than 15th magnitude, Gaia will measure their positions to an accuracy of 24 microarcseconds. This is comparable to measuring the diameter of a human hair at a distance of 1000 km. It will allow the nearest stars to have their distances measured to the extraordinary accuracy of 0.001%. Even stars near the Galactic centre, some 30 000 light-years away, will have their distances measured to within an accuracy of 20%. The vast catalogue of celestial objects expected from Gaia’s scientific haul will not only benefit studies of the Solar System and the Milky Way, but also address fundamental physics questions that underpins our entire Universe.

At its heart, the Gaia satellite contains two optical telescopes that work with three science instruments to precisely determine the location of stars and their velocities, and to split their light into a spectrum for analysis. During its originally planned five-year mission, the spacecraft spins slowly, sweeping the two telescopes across the entire celestial sphere. As the detectors repeatedly measure the position of each celestial object, they will detect any changes in the object’s motion through space.

Gaia is mapping the stars from an orbit around the Sun, at a distance of 1.5 million km beyond Earth’s orbit. This special location, known as the L2 Lagrangian point, keeps pace with Earth as we orbit the Sun. It offers a clearer view of the cosmos than an orbit around Earth, which would result in the spacecraft passing in and out of Earth’s shadow and causing it to heat up and cool down, distorting its view. Free from this restriction and far away from the heat radiated by Earth, L2 provides a much more stable viewpoint. 

Gaia is a fully European mission. The spacecraft is controlled from the European Space Operations Centre (ESOC, Darmstadt, Germany) using three ground stations in Spain, Argentina and Australia. Science operations are conducted from the European Space Astronomy Centre (ESAC, Villafranca, Spain). The Gaia Data Processing and Analysis Consortium (DPAC) process the raw data to be published in the largest stellar catalogue ever made.

 

Anthony Brown is an associate professor at Leiden Observatory and has been involved in the ESA Gaia mission since 1997. He currently chairs the Gaia Data Processing and Analysis Consortium, a team of over 400 European astronomers and IT specialists who are in charge of turning the raw measurements from the Gaia spacecraft into a three dimensional map of over one billion stars in our home galaxy, the Milky Way. Anthony is very broadly interested in the astronomical research that can be done with the aid of Gaia data, from studies of our own solar system to understanding the formation history of the Milky Way.

Seminar recorded on November 12, 2020

“INTEGRAL – The Extreme Universe“ with Enrico Bozzo (Department of Astronomy, University of Geneva, Switzerland)

The INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) is a space telescope for observing the sky in the hard X-rays to soft Gamma-rays. It was launched in 2002 into an elongated 3 days-long orbit around the Earth and originally designed to provide for two years imaging and spectroscopy of cosmic sources in an energy domain that was poorly explored at that time. INTEGRAL is a truly international mission. It is led by the European Space Agency (ESA) in collaboration with many ESA member states and features also a substantial participation from United States and Russia.

INTEGRAL is equipped with a complex and robust suite of complementary instruments, providing overall a wide energy coverage, ranging from 3 keV to about 10 MeV. These instruments are capable of performing observations of cosmic sources with good spectroscopy and good imaging capabilities, providing also a high cadence monitoring of large fractions of the sky at once in both the X-ray and optical energy bands.

As of today, INTEGRAL is the only spacecraft of the European Space Agency (ESA) fleet performing scientific observations in the hard X-rays to Gamma-ray domain. Its principal targets are violent explosions known as gamma-ray bursts, powerful phenomena such as supernova explosions, and regions in the Universe thought to contain black holes and other compact objects. In the past two decades, the mission has greatly improved our understanding of the variable and transient Universe, providing, among others, the first detection of radioactive decays in the material expelled after a Supernova explosion, detailed mapping of the super-bubbles produced by supernovae and massive stars in the Milky Way though a spatially resolved image of the sky in the energy range of the 26Al unstable radioactive isotope line, and gamma-ray polarimetric measurements of the emission from bright black-hole binaries. Since 2002, INTEGRAL is also providing unique means to discover peculiar hard X-ray transient sources that so much have to teach us about physics under extreme conditions.

Among these sources, we find the accreting millisecond X-ray pulsars, which are key objects for understanding the physics of matter at supra-nuclear densities; the supergiant fast X-ray transients, which are the gates to understand potential implications of super-strong magnetic fields onto accretion processes; and last but not least, black-hole binaries, which give us unique data to understand the formation and evolution of accretion disks, as well as the production of jets and other ejection mechanisms (as for example ultra-fast outflows).

In 2013, INTEGRAL has provided the decisive observational evidence to validate the so-called pulsar recycling scenario by discovering the first truly swinging pulsar between radio and X-rays. In 2020, INTEGRAL has firmly established the long-sought association between fast radio bursting sources and super-strongly magnetized neutron stars. During every year of INTEGRAL operations, new kinds of transient hard X-ray to Gamma-ray emitters are being discovered. Each object provides the community with unique opportunity to study high energy physical processes in different environments and comprehend the ramifications of evolutionary paths.

INTEGRAL has far exceeded its originally planned lifetime but still today, after more than 18 years of successful operations in space, it is providing the international community with yet breakthrough discoveries and unique observational capabilities. The key role played by INTEGRAL in the discovery of the first counter-part to a gravitational wave event in 2017 has given further new life to the mission. It has now been widely recognized that INTEGRAL is a fundamental partner in the huge multi-wavelength effort being put in place to hunt for future counterparts of gravitational wave sources, as well as Neutrino sources.

Enrico Bozzo got his PhD in Astronomy at the University of Rome. After a first post-doc in Rome, he moved in 2009 to the INTEGRAL Science Data Center in Versoix, Department of Astronomy of the University of Geneva, Switzerland. Dr. Bozzo’s main scientific interest is focused on accreting X-ray binaries hosting neutron stars, both from a theoretical and observational perspective. He is involved in the development of future space missions for Astronomical and Astrophysical research, including Euclid, THESEUS, eXTP, and Athena. For the INTEGRAL mission, he is co-cordinating since 2009 part of the science ground segment operations, involving the overviewing of the data processing and distribution to the community, as well as the quick-looking.

Seminar was recorded on November 5, 2020

“The Earth, a Planet like no Other” – Online Presentation with Anny Cazenave

The extraordinary talk will take place on Friday, November 13, 18h CET and can be attended online at https://bit.ly/37J001Z (Zoom Webinar).

Meeting ID: 846 6905 4306         Password: 972498

Abstract: The Earth is the only planet of the Solar System hosting evolved life. «How to build an habitable planet ?» has led to considerable scientific literature in the recent decades and has strongly motivated research on exoplanets. All along its history the Earth has displayed specific chemical and physical properties, including a relatively stable climate that a played major role in the evolution of living organisms. In this presentation we discuss the physical particularities of planet Earth, such as gravity and magnetic fields, rotation, mantle convection and plate tectonics, volcanism and water cycle, and their impacts on climates and life, from paleo times to present. Today, Homo Sapiens polulation is approaching 8 billions, a factor 8 times larger than 2 centuries ago, and an indirect consequence of fossil energy use and associated technological innovation. However, our present-day world is facing a number of new «Grand Challenges», as summarized by the United Nations (UN) 2030 Agenda for Sustainable Development. By providing invaluable information on the Earth system and its evolution under natural and anthropogenic forcing factors, Earth observation from space has a key role to play for reaching several of the 17 Sustainable Development Goals of the UN 2030 Agenda, in particular those related to current climate change, water resources, land and marine biodiversity and food security.

 

Anny Cazenave received her Ph.D. in geophysics in 1975 from the University of Toulouse. Subsequently, working at the French space agency CNES, she went into space geodesy, the use of satellites to track changes in Earth’s surface, gravity field and orientation in space. She first focused on the dynamics of the oceanic crust and the mechanically strong layer of the uppermost mantle below it. Among other things, she used early space- borne radars to show that the ocean surface is not flat, but follows the topography of the ocean floor. In other early work, she addressed questions about the rotation of Venus and the origins of the Mars moons, Phobos and Deimos.

Towards the end of last century, European and American space agencies launched a new series of satellite radar altimeters capable of monitoring sea level everywhere in the world oceans in more or less real time. By the early part of the 21st century, it had been determined that global sea level was rising by at least about three millimetres a year. As one of the leading scientists in the joint French/American satellite altimetry missions, TOPEX/Poseidon, Jason-1, and the Ocean Surface Topography Mission, Anny Cazenave has contributed to a greater understanding of this sea level rise and its dependence on global warming.

Besides a large number of publications, Anny was lead author of the sea level sections of the Intergovernmental Panel on Climate Change’s most recent full reports, in 2007 and 2014.

Since 2013, she has been director of Earth sciences at the International Space Science Institute in Bern. In 2020, she received the prestigious Vetlesen Prize, often referred to as the Nobel Prize in geophysics, for her pioneering work in using satellite data to chart and quantify rises in the surface of the oceans, and related changes in ice sheets, landmasses and freshwater bodies.

 

 

Recently, a SPATIUM issue on Climate Change and Sea Level Rise by Anny Cazenave was published by the Association Pro ISSI.

How Water Explains Missing Planets

by Arian Bastani, NCCR PlanetS, University of Bern

Space exploration telescopes have revealed that planets between the size of 1.3 and 2.4 Earth radii seem to be comparatively rare. Scientists under the lead of the International Space Science Institute and the National Centre of Competence PlanetS have found a remarkably simple explanation.

Since 1995, scientists have found over 4000 planets outside the boundaries of our solar system. Some very small, with as little as a third of Earth’s radius. Other very large, up to 20 times wider than our home planet. These extremes are rare, however. Most known planets measure between 1 and 4 times the radius of Earth.

Within this range of common planet sizes, two were found particularly often: Planets with 1.3 and 2.4 Earth radii. “Sizes between these two peaks are much less common and thus form the so-called radius-valley”, Julia Venturini, lead author and researcher at the International Space Science Institute explains. In a study published in the journal Astronomy and Astrophysics, she and her collaborators have now demonstrated why this could be the case.

 

Water or no water

“We found that it has to do with the formation of planets”, Venturini explains “namely the regions in which the planets form”. Previous studies had been able to account for the radius-valley, but only by limiting the formation of the planets to a specific region around their star. Within this region, no condensed water exists. Thus, such planets would be dry. But, as Venturini points out: “This is at odds with planet formation theory. Planets form very easily beyond the ice line (the cold region of around the star beyond which water condenses), accrete plenty of water, and then typically migrate inwards, ending up closer to the star”.

An illustration of the planet formation within and beyond the ice-line. The planets that form further out grow more massive due to the accumulation of larger icy pebbles. After formation, the planets move closer to the star. Credits: Julia Venturini

 

The solution that Venturini and her colleagues came up with imposes no such limitations on the planets’ formation location. “We found that planets which form only out of dry rocky material stay much smaller than ones that also accumulate ice as they grow”, she explains. “This has to do with the different collisional properties of rocks and ice”. Using computer models, they could reproduce the radius-valley based on these distinct formation regions, separated by the so-called ice-line. Thus, the first common planet size of around 1.3 Earth radii comes from dry terrestrial planets and the second group around 2.4 Earth radii mostly consists of water-rich worlds.

 

Sketch of the two peaks of common planet sizes with dry and water-rich planets, as well as the radius-valley between them, as computed by Venturini et al. (2020). Credits: Julia Venturini

 

Time and new telescopes will tell

“These results could help us with preliminary characterizations of planets beyond our solar system”, Venturini hopes. But they first have to be confirmed. With the development of ever more sophisticated telescopes, such as the planned Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL) of ESA, the compositions of faraway planets could be revealed in more detail and would thus allow to test the results of Venturi and her colleagues.

Julia Venturini is a postdoctoral research fellow at the International Space Science Institute (ISSI)

Reference: Julia Venturini, Octavio M. Guilera, Jonas Haldemann, Mari­a P. Ronco, Christoph Mordasini: The nature of the radius valley: Hints from formation and evolution models, A&A 643, L1 (2020) https://www.aanda.org/10.1051/0004-6361/202039141

Press Release NCCR Planet S (28 October 2020)

Contact: Dr. Julia Venturini, International Space Science Institute, Telephone + 41 31 631 48 86
Email: Julia.Venturini@issibern.ch

“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