“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.

“Juno: Revealing the Mysteries of Jupiter” with Ravit Helled (University of Zurich, Switzerland)


Juno was launched in August 2011 to arrive at Jupiter almost five years later. Juno is the first Jupiter mission on a polar orbit. It is a NASA New Frontiers mission and its goals are to understand the origin and the evolution of the planet, to study Jupiter’s interior structure, in particular look for evidence for a heavy-element core and determining its bulk composition, map the gravity and magnetic fields of the planet and map the magnetosphere, measure water and ammonia in the planet’s deep atmosphere, and observe auroras. The mission is ongoing and scheduled to end by having Juno deorbit and dive into Jupiter’s atmosphere in July next year where the spacecraft would be destroyed. Juno’s orbit has a large eccentricity and thus the mission is particularly suited to explore the planet’s magnetosphere and gravity field. Juno is the first mission to Jupiter that relies solely on solar energy thanks to its orbit. The orbit is also well suited to deal with the strong radiation level around the planet.

The question of heavy-element cores in giant planets is one of long-standing interest in planetary science due to its direct connection to planet formation theory. Before the Juno mission, some models of the interior structure allowed cores of masses of several times the Earth’s mass (or even larger), while other models concluded that a core is not necessary to explain the planet’s gravity field features. Juno gravity data imply that Jupiter’s interior is inhomogeneous in composition, and that it is likely to have a “fuzzy” core.

Another question of long-standing interest is the origin of Jupiter’s magnetic field. It is undisputed that a dynamo is at work – in some way similar to the dynamo that generates the Earth’s magnetic field in its core. But the dynamo is not located in Jupiter’s core but at depths where hydrogen becomes metallic and behaves like a metal. It is also still unknown how the dynamo is powered. Accurately mapping Jupiter’s magnetic field helps to understand the dynamo mechanism and can also be used to further constrain the internal structure.

The Juno spacecraft carries a plaque remembering Galileo Galilei and three mini Lego figures (but made of aluminum rather than plastic because of the more challenging space environment) representing Galileo and the roman gods Jupiter and Juno.

Prof. Ravit Helled is professor at the Center for Theoretical Astrophysics and Cosmology of the Institute for Computational Science at the University of Zurich. She is a member of the Juno science team and a highly cited and respected expert for the interior structure of giant planets and their formation in the solar system and beyond.

This Seminar was recorded on September 10, 2020

From the Interstellar Medium to Comets: The Case of Hydroxylated Silicates in 67P/Churyumov–Gerasimenko

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

Recent investigations of the surface composition of comet 67P/Churyumov-Gerasimenko, by means of observations provided by the VIRTIS imaging spectrometer onboard the Rosetta mission, revealed the presence of aliphatic organics and ammonium salts, which characterize the ubiquitous 3.2 µm absorption band in the comet’s infrared spectrum. (See ISSI Team Report from April 9, 2020)

Here we report of a further laboratory investigation, which indicates that hydroxylated magnesium-rich amorphous silicates have spectral properties compatible with the infrared absorption observed on the comet 67P/Churumov-Gerasimenko. They can be an additional constituent of the comet’s surface. Hydroxylated amorphous silicates are formed upon interaction of hydrogen atoms with amorphous silicates. Such process can take place in the interstellar medium (ISM), and the presence of hydroxylated silicates on a cometary nucleus would represent an evolutionary linkbetween the ISM and the primitive objects in the Solar System. The link is consistent with the evolution of aliphatic organics, which also originate in the ISM.

The investigation took advantage, among other authors, of the collaboration of the ISSI Team “Comet 67P/Churyumov-Gerasimenko Surface Composition as a Playground for Radiative Transfer Modeling and Laboratory Measurements” led by M. Ciarniello and has been published in the paper

Hydroxylated Mg-rich Amorphous Silicates: A New Component of the 3.2 μm Absorption Band of Comet 67P/Churyumov–Gerasimenko by V. Mennella et al., 2020, The Astrophysical Journal Letters, Volume 897, Number 2, DOI: https://doi.org/10.3847/2041-8213/ab919e

“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

ISSI Tuesday Tea(m) Time 1551

Report by Joachim Wambsganss, ISSI Director

Following the interruption of the usual activities at ISSI in Bern due to the Corona crisis, the ISSI directorate discussed other/new/additional ways to promote and enable international space science. We came up with three new initiatives, the first of which started on July 14, 2020: ‘ISSI Tuesday Tea(m) Time 1551’ and will be presented here.

The idea behind it is as follows: Due to national and international travel restrictions, regular full physical meetings at ISSI Bern are presently difficult. This is of particular concern to the ISSI International Teams. International Teams consist of 8 to 15 scientists and typically meet in Bern at the ISSI premises two or three times within roughly two years. At any given time, about 50 International Teams are “active”. Since mid-March, no meeting of an International Team has taken place at ISSI although the first physical meetings will likely resume in September.  

To provide support to International Teams, the ISSI directorate came up with the suggestion to meet “virtually” in form of video conferences. In order to structure this and to give ISSI scientists a chance to participate, we fixed a weekly slot, Tuesdays at 15:51 o’clock Bern time (i.e. CEST or CET, respectively). So ideally, every Tuesday a different team shall meet within the next so many months. The slightly odd-looking time-of-day was chosen because the numerals 1551 look very similar to the letters ISSI and hence have a visual connection and can be easily remembered as well. Since on one hand, this afternoon time is when many cultures celebrate a cup of tea, on the other hand we want each ISSI Team to use this opportunity, we call this new activity: 

ISSI Tuesday Tea(m) Time 1551

(or in short ISSI TTT 1551). Most of the International Teams responded positively, some embraced this new opportunity of a soon-to-be-held team meeting enthusiastically.

The first actual “ISSI TTT 1551”-event took place on Tuesday this week, July 14, 2020. The ISSI International Team An Exploration of the Valley Region in the Low altitude Ionosphere: Response to Forcing from Below and Above and Relevance to Space Weather lead by Jorge Chau (Leibniz Institute of Atmospheric Physics, Rostock, Germany) met online via the ZOOM system, the session had been prepared by ISSI.

Screenshot of the first Tuesday Tea(m) Meeting with the J. Chau Team and ISSI Staff Members

 

 

 

 

 

 

 

 

 

 

 

 

 

This “ISSI TTT 1551”-premiere worked very well. After a few introductory words by ISSI representatives, the team chair Koki Chau presented a draft agenda for the meeting. First some administrative issues were discussed, e.g. whether the next envisioned physical meeting team meeting at ISSI Bern – foreseen for end of September – could or should be held, maybe combined as a hybrid meeting with remote participation possible. Then the team discussed how to proceed with another new ISSI activity, namely an ISSI@25 video, meant to celebrate 25 years of ISSI with a 25 second video per International Team (this will be reported about in the near future with a separate spotlight). Following a brief status of activities, three short science talks (10 min each) were presented by team members followed by a Q&A period. A general discussion concluded the meeting.

This first ISSI TTT 1551 was an excellent realization of our vision at ISSI of how such a meeting should work. Five ISSI staff members participated, at least for part of the time. They enjoyed the opportunity to meet the team and get an excellent impression on what their science is all about as well as of the enthusiasm of the team members. This team was an excellent pioneer and did extremely well from our ISSI perspective. We certainly hope that the team enjoyed their Tea Time as well. We look forward to many more interesting and exciting ISSI TTT 1551 events with other active ISSI International Teams in the coming months!

3He-rich Solar Energetic Particles Observations at Parker Solar Probe

Report from ISSI Team #425 Origins of 3He-Rich Solar Energetic Particles led by R. Bucik and J.F. Drake 

Left: Mass histogram for 3He-rich SEP event on 2019 April 20 shows small but clear 3He peak. Right: Jet observations at the west limb from the SDO/AIA. Adapted from Wiedenbeck et al. (2020).

3He-rich solar energetic particles (SEPs) are one of the most peculiar and least explored particle populations in the heliosphere with a tremendously enhanced abundance of the 3He nuclide and ultra-heavy elements (e.g., Pb) by a factor up to 104 above the solar corona or solar wind. One reason for the current lack of understanding of 3He-rich SEPs is the small size of these events. Recently launched Parker Solar Probe (PSP) is able to approach the solar sources of 3He rich SEPs at distances (~0.05 au; 1 au ~ 1.5⨉108 km) that have never been reached before. On 2019 April 20-21, the IS⊙IS energetic particle suite on PSP made its first observations of 3He-rich SEPs. 3He-rich SEPs were observed at energies near 1 MeV/nuc in association with energetic protons, heavy ions, and electrons. At the time of 3He-rich SEP observations, the spacecraft was near 0.46 au. The event was also detected by ULEIS and EPAM on Advanced Composition Explorer (ACE) spacecraft, located near Earth, at 0.99 au from the Sun. The average intensity at ~ 1 MeV/nuc was a factor ~4 greater at PSP than at ACE, which might be attributable to a 1/r2 dependence of the fluence, where r is a distance from the Sun. At that time, PSP and ACE were both magnetically connected to a location near the west limb of the Sun. Remote sensing measurements showed the presence of a type III radio burst and also a helical unwinding jet from this region of the Sun. This activity, which is commonly associated with 3He-rich SEP acceleration on the Sun, originated from the active region number AR 12738. We also searched for smaller 3He-rich SEP events that are not observable near the Earth but might have been detectable closer to the Sun because of the expected strong radial dependence of the intensities of SEP events impulsively released from localized sources. Although no such events were detected during the first two orbits of PSP, this search will be continuing as PSP moves progressively closer to the Sun, and as solar activity increases. These observations should enable IS⊙IS to make significant progress in understanding small 3He-rich SEP events.

 

Animation of the Jet observations at the west limb from the SDO/AIA. Adapted from Wiedenbeck et al. (2020).

 

Reference

Wiedenbeck M.E., Bucik R., Mason G.M., Ho G.C., Leske R.A. et al., 3He-rich Solar Energetic Particle Observations at Parker Solar Probe and Near Earth, Astrophys. J. Suppl. Ser. 246, 42, 2020.