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Future exploration of the ice giants
Scientific discussion meeting organised by Dr Leigh Fletcher, Dr Adam Masters, Dr Athena Coustenis, Dr Kathleen Mandt, Dr Ian Cohen, Dr Christopher Arridge and Dr Amy Simon.
Uranus and Neptune are our closest representatives of a class of planet that may be commonplace in our universe, and yet our exploration and understanding of these icy worlds is in its infancy. This meeting aimed to shape the key questions, motivations, and concepts for future collaborative missions to these tantalising destinations.
Speaker biographies and abstracts are available below. Recorded audio of the presentations is also available below. An accompanying journal issue was published in Philosophical Transactions of the Royal Society A.
Enquiries: contact the Scientific Programmes team
Splinter meeting
A splinter meeting was held following this meeting, details of which can be found on the organisers' website.
Organisers
Schedule
Chair
Dr Leigh Fletcher, University of Leicester, UK
Dr Leigh Fletcher, University of Leicester, UK
Dr Leigh Fletcher is a Planetary Scientist specialising in the exploration of our Solar System’s giant planets via robotic missions and ground-based astronomy. He is a Royal Society University Research Fellow (URF) and Associate Professor in Planetary Sciences at the University of Leicester. He earned a Natural Science degree from Cambridge, a PhD in Planetary Physics from Oxford, and has since worked as a NASA fellow at the Jet Propulsion Laboratory and as a Research Fellow at Oxford. He received the 2016 Harold C Urey prize for outstanding achievements in planetary science by an early-career scientist, awarded by the Division for Planetary Sciences of the American Astronomical Society. He is a co-investigator on the Cassini mission to Saturn, the JUICE mission to Jupiter, and a passionate advocate for future exploration of the distance Ice Giants. He currently leads a planetary atmospheres team at the University of Leicester, funded by the Royal Society, STFC, and the European Research Council.
| 09:00 - 09:05 |
Welcome by the Royal Society and Leigh Fletcher
The Ice Giants, Uranus and Neptune, have never had a dedicated robotic explorer. What little we know of these worlds comes from a brief flyby more than three decades ago, combined with challenging remote observations from ground- and space-based facilities. Missions during the first decades of the 21st century have returned to Jupiter (Galileo, Juno, and JUICE) and Saturn (Cassini), meaning that a journey to the “frozen frontier” is the next logical step in our exploration of the Solar System. This meeting occurs at a crucial moment in our quest for missions to Uranus and/or Neptune – Ice Giant science may become a cornerstone of both ESA’s Voyage 2035-2050 programme, and the US planetary decadal survey beyond 2022. Meanwhile, celestial mechanics moves Jupiter into the perfect location for gravity-assist trajectories to Uranus and Neptune in the 2029-34 period. If we are to rise to the technological and scientific challenge of exploring these remote worlds, we must continue the spirit of international collaboration, and raise the maturity of our ambitious mission concepts. This three-day workshop will review our knowledge of the Ice Giants at the start of the 2020s, and hopes to set in motion a coordinated international effort to realise an ambitious mission to these worlds before the decade is out. Such a paradigm-shifting mission would define Solar System exploration for a whole generation of planetary scientists, just as Cassini did during the previous decade. |
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| 09:05 - 09:15 |
Meeting objectives
Dr Leigh Fletcher, University of Leicester, UK
Dr Leigh Fletcher, University of Leicester, UKDr Leigh Fletcher is a Planetary Scientist specialising in the exploration of our Solar System’s giant planets via robotic missions and ground-based astronomy. He is a Royal Society University Research Fellow (URF) and Associate Professor in Planetary Sciences at the University of Leicester. He earned a Natural Science degree from Cambridge, a PhD in Planetary Physics from Oxford, and has since worked as a NASA fellow at the Jet Propulsion Laboratory and as a Research Fellow at Oxford. He received the 2016 Harold C Urey prize for outstanding achievements in planetary science by an early-career scientist, awarded by the Division for Planetary Sciences of the American Astronomical Society. He is a co-investigator on the Cassini mission to Saturn, the JUICE mission to Jupiter, and a passionate advocate for future exploration of the distance Ice Giants. He currently leads a planetary atmospheres team at the University of Leicester, funded by the Royal Society, STFC, and the European Research Council. 
Dr Amy Simon, NASA Goddard Spaceflight Center, USA
Dr Amy Simon, NASA Goddard Spaceflight Center, USADr Amy Simon is the Senior Scientist for Planetary Atmospheres Research at the NASA Goddard Space Flight Center (GSFC). She joined NASA in 2001, following a postdoctoral position at Cornell University. Dr Simon’s scientific research focuses primarily on the composition, atmospheric structure, and dynamics of the atmospheres of Jupiter, Saturn, Uranus, and Neptune from analysis of spacecraft data. She is the Principal Investigator of the Hubble Outer Planet Atmospheres Legacy program, and is actively involved in flight mission work, as a co-I on NASA’s Cassini, OSIRIS-REx, and Lucy missions. She served as co-lead of the NASA JPL Ice Giant mission concept study. 
Dr Mark Hofstadter, JPL/Caltech, USA
Dr Mark Hofstadter, JPL/Caltech, USADr Hofstadter has over 25 years' experience in Planetary Science, including ground- and space-based observing, mission design and operations, technical and personnel management, teaching, and public outreach. His research primarily involves microwave remote sensing of giant planets and comets, but he has also published work related to the Earth, Mars, and asteroids. He is the PI of a NASA instrument (MIRO) which flew on board the European Space Agency's Rosetta spacecraft. Dr Hofstadter served as Co-Chair of a NASA Science Definition Team investigating possible future missions to Uranus and Neptune, and currently serves on the Steering Committee of NASA's Outer Planets Assessment Group (OPAG). He is a member of the DPS, AGU, and EGU scientific organizations. Dr Hofstadter received a BS degree in Physics from Stanford University and MS and PhD degrees in Planetary Science from Caltech. |
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| 09:15 - 09:45 |
Origin, evolution, and internal structure of the ice giants
There are many open questions regarding the nature of Uranus and Neptune, the outermost planets in our Solar System. This presentation will briefly summarise the current-knowledge about Uranus and Neptune with a focus on their formation, thermal evolution, and internal structure. According to standard planet formation theories, the masses of Uranus and Neptune lie in a regime where planets are expected to accrete gas rapidly and become giant planets. Therefore, the termination of gas accretion at the mass of the ice giants needs to be explained. This presentation will present various formation scenarios that can explain their observed properties and discuss the connection to planet formation theory and for our understanding of exoplanets. It will also briefly discuss the possibility and outcomes of giant impacts on Uranus and Neptune and the connection to their observed differences. Finally, it will present non-standard internal structure models of the planets, suggesting that they are likely to have non-adiabatic interiors with no-distinct layers, and question whether they are indeed “icy" planets. 
Professor Ravit Helled, University of Zurich, Switzerland
Professor Ravit Helled, University of Zurich, SwitzerlandRavit Helled is a Planetary Scientist and a Professor for Theoretical Astrophysics at the Institute for Computational Science, Center for Theoretical Astrophysics & Cosmology, University of Zurich. Prof. Helled has received her PhD in 2008 from Tel-Aviv University on the topic “The Formation of Jupiter". She has been a postdoc and senior researcher at the University of California, Los Angeles (2007-2011), and then a professor at Tel Aviv University (2011-2016), until she moved to Zurich, Switzerland in 2016. Her scientific work concentrates on planet formation & evolution, planetary interiors, and extrasolar planets. Prof. Helled has published many scientific papers, is a frequent invited speaker in international conferences, and often serves as a reviewer in committees and science panels. Prof. Helled is strongly involved in Space exploration and is involved in several ESA and NASA space missions |
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| 09:45 - 10:15 |
Interior structure and energy balance of Jupiter and Saturn
Dr Jonathan Fortney, University of California, Santa Cruz, USA
Dr Jonathan Fortney, University of California, Santa Cruz, USAJonathan Fortney is a Professor in the Department of Astronomy & Astrophysics at the University of California, Santa Cruz, and the Director of the university’s Other Worlds Laboratory. Professor Fortney is a theorist and modeller who works to understand the interiors, atmospheres, and thermal evolution of planets inside and outside the solar system. He has been a member of the science team of NASA’s Cassini Mission to Saturn and NASA’s Kepler Mission to find planets in orbit around other stars. Professor Fortney has a particular interest in the structure and composition of the solar system’s giant planets, and trying to make connections with the numerous exoplanets of similar masses that have been found around other stars. Recognition for his work includes a Sloan Research Fellowship and the Urey Prize from the American Astronomical Society’s Division for Planetary Sciences. |
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| 10:15 - 10:30 | Discussion – interiors objectives | |
| 10:30 - 11:00 | Coffee break | |
| 11:00 - 11:25 |
Atmospheric dynamics and cloud structure of the ice giants
Dr Ricardo Hueso, University of Bilbao, Spain
Dr Ricardo Hueso, University of Bilbao, SpainRicardo Hueso (Bilbao, Spain, 1973). Dr R Hueso studied physics at the University of the Basque Country (UPV/EHU) where he graduated in Physics. He obtained his PhD in Physics at the same University in 2000, with a thesis on the 'Atmosphere dynamics of large-scale storms in the Giant Planets'. He moved to the Observatoire de la Côte d’Azur where he studied early stages of protoplanetary disks with applications to the study of the Solar System formation and the giant plants. He was a 'Ramon y Cajal Fellow' in the UPV/EHU in Spain from 2006–2009 where he continued working on atmospheric dynamics of different Solar System planets from Venus to Neptune including Saturn's moon Titan. He is currently an Assistant professor at the Faculty of Engineering in the UPV/EHU where his work involves astronomical observations, numerical modeling, data analysis from different space missions, frequent collaborations with amateur astronomers and teaching. |
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| 11:25 - 11:50 |
Photochemistry in the atmospheres of Uranus and Neptune
Dr Julianne Moses, Space Science Institute, USA
Dr Julianne Moses, Space Science Institute, USAJulianne I. Moses is a Senior Research Scientist at the Space Science Institute (SSI), which is based in Boulder, Colorado, USA. She received her undergraduate degree in physics (with honors) from Cornell University in 1985 and her PhD in planetary science and geophysics from the California Institute of Technology in 1991. Her research expertise is in physical and chemical processes in planetary and satellite atmospheres, with a particular emphasis on photochemical and thermochemical kinetics modeling of giant planets and extrasolar planets, aerosol formation and dynamics, upper atmospheric structure and chemistry, and atmosphere-surface interactions. |
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| 11:50 - 12:15 |
The upper atmospheres of the ice giants
The upper atmosphere of a giant planet plays an important role as the interface layer between the lower atmosphere below and the magnetosphere beyond. It has two basic components: the neutral thermosphere and the charged particle ionosphere. The ionosphere senses the magnetic field whilst the thermosphere is affected by dynamical processes in the lower atmosphere. Understanding momentum transfer between these systems becomes critical in understanding the energy balance of the atmosphere and magnetosphere as a coupled system. The ionosphere can be sensed remotely from the ground via spectral observations of the molecular ion H3+ which reveal the temperature of the upper atmosphere and ion density of this region. H3+ was discovered at Uranus in 1992 and we have a 27 year baseline of observations that reveal that the upper atmosphere is subject to long-term cooling that may be related to the extreme seasons of Uranus. However, the 2007 equinox did not offer a reversal in this trend, and as of 2018 continued cooling has been observed. Surprisingly, H3+ remains undetected at Neptune, with the upper limit of the ionospheric density being much lower than predicted by models. Finally, Dr Melin will discuss how future facilities, including dedicated spacecraft missions, can enhance our understanding of the ionosphere of Uranus and Neptune. 
Dr Henrik Melin, University of Leicester, UK
Dr Henrik Melin, University of Leicester, UKDr Henrik Melin is an expert in analysing ground-based and spacecraft observations of the giant planets. He obtained his PhD in planetary science from University College London in 2006, working with Professor Steve Miller on ground-based infrared observations of H3+ from Jupiter, Saturn, and Uranus. Henrik spent his first postdoc in Los Angles, working on ultraviolet data from the Cassini spacecraft, mapping neutrals inside the magnetosphere of the planet. Returning to the UK in 2009, he settled in at the University of Leicester, working to combine spacecraft and ground-based observations of the giant planets, studying the entire column of atmosphere, from the troposphere, through the stratosphere and up to the thermosphere. |
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| 12:15 - 12:30 | Discussion 2 – Atmospheric objectives |
Chair
Dr Amy Simon, NASA Goddard Spaceflight Center, USA
Dr Amy Simon, NASA Goddard Spaceflight Center, USA
Dr Amy Simon is the Senior Scientist for Planetary Atmospheres Research at the NASA Goddard Space Flight Center (GSFC). She joined NASA in 2001, following a postdoctoral position at Cornell University. Dr Simon’s scientific research focuses primarily on the composition, atmospheric structure, and dynamics of the atmospheres of Jupiter, Saturn, Uranus, and Neptune from analysis of spacecraft data. She is the Principal Investigator of the Hubble Outer Planet Atmospheres Legacy program, and is actively involved in flight mission work, as a co-I on NASA’s Cassini, OSIRIS-REx, and Lucy missions. She served as co-lead of the NASA JPL Ice Giant mission concept study.
| 13:30 - 13:55 |
Dynamos of ice giant planets
The magnetic fields of Uranus and Neptune are non-axisymmetric and multipolar with quadrupole and octupole components that are comparable to or greater than the dipole. At present, spherical harmonics greater than degree four are below the limits of spatial resolution, and there is no information about any secular variations. Because of these unique characteristics, the ice giants serve as excellent laboratories for determining the fundamental dynamical and chemical processes responsible for generating all planetary magnetic fields. Magnetic fields originate in the electrically conducting fluid regions of planetary bodies and likely result from convectively driven dynamo action. Consequently, an understanding of the dynamo processes that control the magnetic field strength, morphology, and temporal evolution of ice giant planets is critically dependent on their poorly constrained interior structures, bulk compositions, heat balance, and dynamics. It is typically assumed that the magnetic fields are generated in the planets’ “watery” oceans. Moreover, if the transition between the watery ocean and the overlying atmosphere is continuous, these two regions may be dynamically coupled, linking the dynamo to atmospheric dynamics and its thermal emissions. A variety of competing numerical dynamo models have been developed to explain the ice giants’ magnetic fields. Additional constraints derived from a second mission to Uranus and/or Neptune would test these hypotheses, aid in development of more realistic models, and yield better predictions about the evolution of planetary magnetic fields. 
Dr Krista Soderlund, University of Texas at Austin, USA
Dr Krista Soderlund, University of Texas at Austin, USAKrista Soderlund is a planetary geophysicist broadly interested in fluid dynamic processes. She is a Research Scientist at the University of Texas Institute for Geophysics (UTIG), previously earning dual BSc degrees in Physics and Space Sciences from the Florida Institute of Technology in 2005 and a PhD in Geophysics and Space Physics from the University of California, Los Angeles in 2011. She uses numerical models to simulate convection and magnetic field generation within planetary interiors and to study icy satellite oceans and ice shells. Soderlund is also a science team member of the ice-penetrating radar instrument (REASON) on the Europa Clipper mission and served recently on NASA's Ice Giant Mission Study Science Definition Team. |
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| 13:55 - 14:20 |
Ice giant magnetospheres
Dr Carol Paty, University of Oregon, USA
Dr Carol Paty, University of Oregon, USADr Carol Paty is a planetary and space physicist interested in the planetary magnetospheric dynamics and the complex interactions between moons, magnetospheres and ionospheres. She is an Associate Professor at the University of Oregon in the Department of Earth Sciences and in the Clark Honors College. She earned her PhD in Geophysics and Space Physics at the University of Washington and her BA in Physics and Astronomy from Bryn Mawr College. Her research develops 3-dimension numerical simulations to provide a context for integrating and interpreting diverse datasets collected by in situ and remote sensing techniques. She was a participating scientist in NASA's Cassini Mission to Saturn, and is currently a Co-Investigator on the Europa Clipper mission and Jupiter Icy Moons Explorer mission. She is also actively involved in proposals and white papers to inspire a future mission to the Ice Giant systems. |
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| 14:20 - 14:45 |
Ice giant aurora
Uranus and Neptune possess internal magnetic fields with similar characteristics (largely tilted, offset and multipolar) which interact with the solar wind form to ‘twin’ asymmetric magnetospheres unique in the solar system. Our current knowledge of their auroral processes, and of the underlying solar wind-magnetosphere-ionosphere interaction, still mostly relies on Voyager 2 radio/UV and in situ observations obtained during the flyby of each planet, respectively in 1986 and in 1989. These observations were acquired at epochs corresponding to specific solar wind/magnetosphere configurations, expected to vary significantly for both planets along their revolution around the Sun. Fortunately, while waiting for future in depth exploration missions of ice giant planets, some additional clues were in-between obtained from remote long-term Earth-based UV/IR observations which sampled different seasons and reveal strongly different solar wind/magnetosphere interactions. 
Dr Laurent Lamy, Observatoire de Paris, PSL, CNRS, France
Dr Laurent Lamy, Observatoire de Paris, PSL, CNRS, FranceLaurent Lamy is expert in planetary magnetospheres and auroral physics investigated by the means of modelling, UV and radioastronomy. |
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| 14:45 - 15:00 | Discussion – magnetic field objectives | |
| 15:00 - 15:30 | Tea break | |
| 15:30 - 16:00 |
US perspectives on ice giant missions
In two years, the US Planetary Science Decadal Survey will lay out its vision for the next phase of NASA's activities in the Solar System. Part of that vision will define the first dedicated mission to an Ice Giant planet. The Survey could call for a Flagship-class mission that explores all aspects of an ice giant system. Alternatively, by not prioritizing Ice Giants, it might set the stage for a small Discovery-class competed mission that focuses on more limited objectives. Or perhaps it will lay out a path in between those extremes or one not yet considered. While we do not know what direction will be taken, the importance of Ice Giants to the scientific community has already triggered extensive work to define the broad parameters of possible missions, and to explore ways in which other space agencies could contribute to a NASA-led mission. This talk will review recent and ongoing mission studies and preparations for the Decadal Survey, and discuss some of the programmatic and science trade-offs likely to factor in to the Survey's deliberations. This talk will include a pre-recorded presentation from Dr Lori Glaze, Director of NASA's Planetary Science Division.
Dr Mark Hofstadter, JPL/Caltech, USA
Dr Mark Hofstadter, JPL/Caltech, USADr Hofstadter has over 25 years' experience in Planetary Science, including ground- and space-based observing, mission design and operations, technical and personnel management, teaching, and public outreach. His research primarily involves microwave remote sensing of giant planets and comets, but he has also published work related to the Earth, Mars, and asteroids. He is the PI of a NASA instrument (MIRO) which flew on board the European Space Agency's Rosetta spacecraft. Dr Hofstadter served as Co-Chair of a NASA Science Definition Team investigating possible future missions to Uranus and Neptune, and currently serves on the Steering Committee of NASA's Outer Planets Assessment Group (OPAG). He is a member of the DPS, AGU, and EGU scientific organizations. Dr Hofstadter received a BS degree in Physics from Stanford University and MS and PhD degrees in Planetary Science from Caltech. |
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| 16:00 - 16:30 | ESA perspectives on Ice Giant Missions | |
| 16:30 - 17:00 | Discussion – individual agencies and mission proposals |
Chair
Dr Mark Hofstadter, JPL/Caltech, USA
Dr Mark Hofstadter, JPL/Caltech, USA
Dr Hofstadter has over 25 years' experience in Planetary Science, including ground- and space-based observing, mission design and operations, technical and personnel management, teaching, and public outreach. His research primarily involves microwave remote sensing of giant planets and comets, but he has also published work related to the Earth, Mars, and asteroids. He is the PI of a NASA instrument (MIRO) which flew on board the European Space Agency's Rosetta spacecraft. Dr Hofstadter served as Co-Chair of a NASA Science Definition Team investigating possible future missions to Uranus and Neptune, and currently serves on the Steering Committee of NASA's Outer Planets Assessment Group (OPAG). He is a member of the DPS, AGU, and EGU scientific organizations. Dr Hofstadter received a BS degree in Physics from Stanford University and MS and PhD degrees in Planetary Science from Caltech.
| 09:00 - 09:25 |
Lessons learned from (and since) the Voyager 2 flybys of Uranus and Neptune
More than 30 years have passed since the Voyager 2 fly-bys of Uranus and Neptune. What lessons can we glean from the intervening decades? Dr Hammel will discuss a range of topics that can be broadly grouped into process, planning, and people. PROCESS. We must be open to new concepts. Reliance on existing instrument technologies, propulsion systems, and operational modes is inherently limiting. Dr Hammel will cite examples of each during recent decades that could open new vistas in exploration of the deep outer Solar System. PLANNING. Mission gaps stretching over three decades leaves much scope for evolution both in mission development and in the targets themselves. She will touch only briefly on the planetary system science, as that will likely be covered in other talks. The role of the decadal surveys will be examined in this section. She will also sketch out how coordinating distinct and divergent international planning time-lines yields both challenges and opportunity. PEOPLE. Finally, with generational length gaps between missions, ensuring continuity in knowledge and skills requires careful attention to people. As the youngest participants in the Voyager missions (myself included) near retirement age, we and our elders reflect on lessons learned to pass on to the next generations. In preparation for this talk, Dr Hammel reached out to fellow Voyager alums for their lesson ideas for preparing the next generation of voyagers. Some lesson titles include: flexibility (embrace your inner naïveté); empower the youth; to build a cathedral; and outreach matters. 
Dr Heidi Hammel, Association of Universities for Research in Astronomy, USA
Dr Heidi Hammel, Association of Universities for Research in Astronomy, USADr Heidi B Hammel received her undergraduate degree from MIT and her PhD from the University of Hawaii. She is currently the Executive Vice President of AURA, a consortium that operates large astronomical observatories, including the Hubble Space Telescope. Dr Hammel primarily studies outer planets; she served on the imaging team for the Voyager 2 Neptune encounter, and has studied Uranus and Neptune extensively with Hubble, Keck, and other facilities. She is an Interdisciplinary Scientist for NASA’s James Webb Space Telescope, and plans to use her guaranteed observing time to study a diverse array of Solar System targets including the outer planets. She has been recognized for both her science and her work in public outreach, including the Sagan Medal and the San Francisco Exploratorium's Public Understanding of Science Award. Asteroid "1981 EC20" was renamed 3530 Hammel in her honour. |
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| 09:25 - 09:50 |
Why Exoplanets need an Ice Giant Mission
Dr Hannah Wakeford, University of Bristol, UK
Dr Hannah Wakeford, University of Bristol, UKDr Hannah Wakeford has just started a new position as a Lecturer in Astrophysics at the University of Bristol, UK where she will lead a group on exoplanet observations – primarily with Hubble and Webb. Hannah received a Masters in Physics with Planetary and Space Physics from the University of Wales: Aberystwyth after completing her master's thesis at the University Center in Svalbard studying the upper polar atmosphere. She received her PhD studying exoplanet atmospheres from the University of Exeter before moving to the USA as a NASA postdoctoral fellow at NASA’s Goddard Space flight center, and then the Giacconi Prize Fellow at the Space Telescope Science Institute in Baltimore. Hannah has worked on exoplanet atmospheres from giant hot gassy worlds down to small terrestrial-like exoplanets for which she received the NASA Robert H Goddard Award for individual scientific achievement. Hannah also hosts a monthly podcast called Exocast: The Exoplanet Podcast and has won numerous awards for her science communication. |
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| 09:50 - 10:15 |
Cross-NASA divisional relevance of an ice giant mission
Dr Abigail Rymer, JHU-APL, Maryland, USA
Dr Abigail Rymer, JHU-APL, Maryland, USAAbi Rymer is a space physicist with over 15 years' experience studying the Outer Planets as part of the Cassini and Juno instrument teams. Originally from North-West England she followed a non-traditional route to academia including running a pub in Preston, Lancashire and Fine Fragrance Research with Proctor and Gamble in Egham, Surrey. Abi led the multi-instrument team that identified the Enceladus auroral footprint at Saturn and as a result developed an interest in cross-disciplinary topics, from magnetic microbes to exoplanet atmospheres. Most recently she is participating as Co-Investigator and Investigation Scientist on the planned Europa Clipper mission to Jupiter and on proposals and White Papers to help motivate a NASA-led mission to a solar system Ice Giant and to promote cross-divisional research opportunities at NASA. |
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| 10:15 - 10:30 | Discussion – summary of knowledge gaps | |
| 10:30 - 11:00 | Coffee | |
| 11:00 - 11:25 |
The rings and inner satellites of Uranus and Neptune
All four giant planets are encircled by distinctive systems of rings and small, inner satellites. These all reside within or near their central planet's Roche limit, the rough boundary within which bodies held together by self-gravity will be disrupted by tidal forces. However, the similarities of the four ring-moon systems end here; in most other regards, they are remarkably diverse. We study these systems for three key reasons: (1) for the information they reveal about the properties, history, and ongoing evolution of the planetary systems of which they are a part; (2) as dynamical analogues for other astrophysical systems such as protoplanetary disks; and (3) for the wealth of fascinating properties and origin scenarios that make them worthy of study in their own right. The inner Uranus system is characterized by ten narrow rings, some quite dense, as well as a variety of more tenuous structures. These are accompanied by thirteen known moons all orbiting interior to Miranda. Nine of these, Bianca through Perdita, comprise the most densely-packed set of moons in the solar system, with orbits so close that their interactions appear to drive chaos over time scales as short as a million years. Neptune has five named rings, all optically thin, interleaved with seven inner moons. The most notable feature is a set of arcs embedded within the Adams ring; two of these have been stable for time scales of decades. This presentation will provide a brief overview of the state of our knowledge and discuss the key scientific questions related to these systems. 
Dr Mark Showalter, SETI Institute, USA
Dr Mark Showalter, SETI Institute, USADr Mark Showalter is a Senior Research Scientist and Fellow of the SETI Institute in Mountain View, California. Most of his research focuses on the dynamics of rings and small satellites in the solar system. Early in his career, he participated in the Voyager flybys of Uranus and Neptune as an associate of the imaging team. He has also been a co-Investigator on the Cassini mission to Saturn and the New Horizons mission to Pluto and the Kuiper Belt. Starting in 2003, his work with the Hubble Space Telescope (HST) led to the discoveries of the two small moons Mab and Cupid, as well as two faint dust rings. More recently, he led the team that discovered Hippocamp, a small inner moon of Neptune. |
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| 11:25 - 11:50 |
The Uranian satellite system
Dr Elizabeth Turtle, JHU-APL, Maryland, USA
Dr Elizabeth Turtle, JHU-APL, Maryland, USADr Elizabeth (Zibi) Turtle is a planetary scientist at the Johns Hopkins Applied Physics Laboratory. Her research combines remote-sensing observations and modelling of geological structures and their implications for planetary surfaces, interiors, and their evolution, including impact cratering and tectonics on satellites and terrestrial planets, and lakes and seasonal weather on Titan. She has participated in the Galileo, Cassini, and Lunar Reconnaissance Orbiter missions, and is the Principal Investigator for the Europa Imaging System (EIS) on Europa Clipper and for the Dragonfly Titan mission concept being studied under NASA's New Frontiers Program. She earned her PhD in Planetary Sciences from University Arizona and her BSc in Physics from the Massachusetts Institute of Technology. |
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| 11:50 - 12:15 |
Triton and the Kuiper Belt connection
Dr Michele Bannister, Queen's University Belfast, UK
Dr Michele Bannister, Queen's University Belfast, UKDr Michele Bannister is a Postdoctoral Research Fellow and Director’s Outreach Fellow at Queen’s University Belfast. An expert in the discovery and characterization of the populations of small worlds in the Solar System, she has been involved in the discovery of more than eight hundred minor planets that orbit beyond Neptune, and in the observation and further study of interstellar objects including 'Oumuamua. A keen advocate of the public discussion of science, Bannister is a frequent guest on the BBC’s Sky at Night. She was honoured in 2017 by the International Astronomical Union with asteroid (10463) Bannister. |
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| 12:15 - 12:30 | Discussion – Satellite/rings objectives |
Chair
Dr Adam Masters, Imperial College London, UK
Dr Adam Masters, Imperial College London, UK
Dr Adam Masters is a lecturer and Royal Society University Research Fellow at Imperial College London. His research within the College’s space and atmospheric physics group focuses on explaining how energy flows through the Solar System via magnetic fields and charged particle motion in space, as well as understanding how different bodies in the Solar System generate magnetic fields in their interiors. His research programme is underpinned by his involvement in spacecraft missions, such as the Cassini-Huygens mission to Saturn and Titan that ended in September 2017, the Jupiter Icy Moons Explorer mission currently being built for launch, and ongoing high-level planning of future missions to Uranus and Neptune.
| 13:30 - 13:55 |
Mission design prospects for the ice giants
The Ice Giants, Uranus and Neptune, are destinations that have thus far been unexplored by orbiter missions. While trajectory and mission design work for prospective missions to these bodies has been performed for decades, new trajectory analysis tools and techniques have significantly improved our ability to evaluate a broad tradespace of potential architectures. This new capability was amply demonstrated in NASA’s recent Ice Giants Pre-Decadal Survey mission study. The study included a broad assessment of mission design options that could enable significant science at these destinations, including dependencies on launch years, mission duration, delivered mass, etc., all of which can be used to inform trades when developing a mission concept. This talk will address the broad findings of this mission design evaluation, as well as illustrating its impact on the four missions chosen for point design study in the report. In addition, the results of a new study will be discussed in which the impact of incorporation of a number of new technologies was investigated to shape a high-performance Ice Giants mission. A particular focus of this recent study was the use of drag-modulated aerocapture, a technology that was not previously incorporated in the point design options developed in the earlier Pre-Decadal study. 
John Elliot, JPL, USA
John Elliot, JPL, USAJohn Elliott is a principal engineer in JPL’s Mission Concept Systems Development group. He is currently leading studies in support of future outer planets exploration in addition to ongoing work in the development of concepts for robotic lunar exploration. He currently serves as lead architect and systems engineer for the Solar System Mission Formulation office and core flight systems engineer on JPL’s A-Team for early mission concept development. His recent tasks have included serving as study lead for NASA’s Ice Giants Pre-Decadal Survey Mission Study, and performing systems engineering and leadership roles on a number of recent Discovery and New Frontiers mission proposals. Mr Elliott’s past experience includes six years in the terrestrial nuclear power industry with Bechtel Corporation in addition to 28 years in aerospace systems at TRW and JPL. |
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| 13:55 - 14:20 |
Enabling technologies for ice planet exploration
Four challenges are common to space flight missions to the outer solar system, especially to the ice giant planets: providing electric power, providing telecommunications of sufficient performance between Earth and the spacecraft, handling the thermal environment, and if the mission involves inserting into orbit at the destination, providing sufficient propulsive capability for that orbit insertion and a useful orbital tour afterward. In addition to communications challenges, missions including atmospheric entry probes involve the challenge of extreme hypersonic atmospheric entry. Fitting the responses to these challenges within the tight time and mass constraints of travel to the farthest reaches of our planetary system is a difficult engineering task involving advanced technologies and difficult trade decisions. This presentation will review appropriate technology options for addressing these challenges, including performance characteristics that influence their applicability envelopes. Optimizing an ice giant mission's science return can require considering some clever and non-intuitive trajectory options. Both ice giants have unusual fundamental characteristics that heavily influence orbit insertion and tour designs. The Uranian system is much like a smaller-scale Jovian system, but Uranus's 98° obliquity makes orbit insertion and transition to a gravity-assist-driven orbital tour very different from a Jupiter mission, and very seasonal. The Neptunian system's single large satellite, Triton, makes it more like the Saturnian system – except that Triton's orbit is retrograde, making a tour there quite different from a Saturnian tour. This presentation will also discuss trajectory design options at both ice giants. 
Dr Thomas R Spilker, Independent Consultant, USA
Dr Thomas R Spilker, Independent Consultant, USADr Thomas R Spilker received his PhD in 1990 from Stanford University's Center for Radar Astronomy, in Radio Science/Electrical Engineering. From there he went directly to JPL, first as a National Research Council (NRC) Resident Research Associate, then as an employee in the Science Division, eventually to the Advanced Mission Concepts Section as a Principal Mission Architect. While at JPL he worked on NASA's Voyager, Cassini-Huygens, and Genesis missions, and ESA's Rosetta mission as a Co-Investigator on the MIRO instrument, spent three years on the NRC Committee on Planetary and Lunar Exploration, and was a member of the Satellites of the Giant Planets panel for the 2013–2022 Planetary Science Decadal Survey. Taking early retirement from JPL in 2012 to pursue consulting, he has worked with mission concepts from Venus to the ice giant planets and beyond. Currently he is the Technology representative for NASA's Outer Planets Assessment Group. |
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| 14:20 - 14:45 |
The development of European radioisotope space nuclear power systems
Radioisotope power systems (RPS) have been in development in Europe as part of a European Space Agency funded programme since 2009. The programme is focused on developing all of the building blocks that will enable Europe to launch and operate RPS powered missions in deep space and in challenging environments on planetary surfaces. The maturity of the technology has now reached a level that it can be incorporated in mission studies targeting the period from the mid 2020s onwards. This presentation describes the state of the art in European radioisotope thermoelectric generators (RTGs) and radioisotope heater units (RHUs). 
Dr Richard Ambrosi, University of Leicester, USA
Dr Richard Ambrosi, University of Leicester, USARichard Ambrosi obtained his PhD from the University of the Witwatersrand, Johannesburg South Africa. He moved to Leicester in 2000 to work on the Swift Gamma Ray Burst Observatory X-ray Telescope as CCD calibration scientist. Between 2003 and 2005 Richard worked on radiation and dust impact on space instruments with a focus on the ESA Gaia mission and planned future X-ray astronomy missions. In 2006 Richard became the UK Technical Lead for the ExoMars X-ray Diffraction instrument MARS-XRD. Since 2008 Richard has been leading the development of radioisotope thermoelectric generators, heater units for the European Space Agency. Richard is currently Director of the MSc in Space Exploration Systems and also Deputy Director of the Space Research Centre at the University of Leicester. Since 2016 Richard has been working on various aspects of the development and delivery of Space Park Leicester. |
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| 14:45 - 15:00 | Discussion – technologies | |
| 15:00 - 15:30 | Tea | |
| 15:30 - 16:00 |
Strategy for coordination 2020+
Dr Amy Simon, NASA Goddard Spaceflight Center, USA
Dr Amy Simon, NASA Goddard Spaceflight Center, USADr Amy Simon is the Senior Scientist for Planetary Atmospheres Research at the NASA Goddard Space Flight Center (GSFC). She joined NASA in 2001, following a postdoctoral position at Cornell University. Dr Simon’s scientific research focuses primarily on the composition, atmospheric structure, and dynamics of the atmospheres of Jupiter, Saturn, Uranus, and Neptune from analysis of spacecraft data. She is the Principal Investigator of the Hubble Outer Planet Atmospheres Legacy program, and is actively involved in flight mission work, as a co-I on NASA’s Cassini, OSIRIS-REx, and Lucy missions. She served as co-lead of the NASA JPL Ice Giant mission concept study.
Dr Mark Hofstadter, JPL/Caltech, USA
Dr Mark Hofstadter, JPL/Caltech, USADr Hofstadter has over 25 years' experience in Planetary Science, including ground- and space-based observing, mission design and operations, technical and personnel management, teaching, and public outreach. His research primarily involves microwave remote sensing of giant planets and comets, but he has also published work related to the Earth, Mars, and asteroids. He is the PI of a NASA instrument (MIRO) which flew on board the European Space Agency's Rosetta spacecraft. Dr Hofstadter served as Co-Chair of a NASA Science Definition Team investigating possible future missions to Uranus and Neptune, and currently serves on the Steering Committee of NASA's Outer Planets Assessment Group (OPAG). He is a member of the DPS, AGU, and EGU scientific organizations. Dr Hofstadter received a BS degree in Physics from Stanford University and MS and PhD degrees in Planetary Science from Caltech. |
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| 16:00 - 17:00 | Panel discussion |