Dynamos of ice giant planets
Dr Krista Soderlund, University of Texas at Austin, USA
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.
Ice giant magnetospheres
Dr Carol Paty, University of Oregon, USA
Ice giant aurora
Dr Laurent Lamy, Observatoire de Paris, PSL, CNRS, France
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.
Discussion – magnetic field objectives
US perspectives on ice giant missions
Dr Mark Hofstadter, JPL/Caltech, USA
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.
ESA perspectives on Ice Giant Missions
Discussion – individual agencies and mission proposals