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| Saturn hexagon | |
|---|---|
| Name | Saturn hexagon |
| Type | Atmospheric vortex |
| Location | North Pole, Saturn |
| Discovered | 1980s |
| Discoverer | Voyager program |
| Notable | Persistent, six-sided jet stream |
Saturn hexagon The Saturn hexagon is a persistent, roughly regular six-sided jet stream pattern encircling the north polar region of Saturn discovered in the late 20th century. It has been observed by multiple missions and observatories and remains one of the most striking and studied features in planetary science, drawing attention from researchers associated with NASA, European Space Agency, and the Jet Propulsion Laboratory. The phenomenon connects investigations spanning the Voyager program, Cassini–Huygens, and ground-based facilities such as the Hubble Space Telescope and the W. M. Keck Observatory.
Initial identification occurred during the Voyager program flybys in 1980–1981 when images from the Voyager 1 and Voyager 2 spacecraft revealed a geometric pattern near the north pole. Subsequent observations were advanced by the Cassini–Huygens mission from the Jet Propulsion Laboratory and the European Space Research and Technology Centre, which provided extensive imaging and spectroscopy between 2004 and 2017. Planetary scientists from institutions including California Institute of Technology, University of Arizona, Cornell University, University of Oxford, and Massachusetts Institute of Technology have analyzed datasets from instruments such as the Imaging Science Subsystem (ISS), Composite Infrared Spectrometer, and Visual and Infrared Mapping Spectrometer. Observations from terrestrial observatories like the Arecibo Observatory (historically), Subaru Telescope, and the Very Large Telescope supplemented spacecraft data, while specialist groups at NASA Ames Research Center, Southwest Research Institute, and Planetary Science Institute performed long-term monitoring. Seasonal changes observed alongside comparisons with data from the Uranus orbiter concept studies and proposals by the European Space Agency show interest in future polar missions.
The hexagon is approximately 29,000 kilometers in diameter, centered on Saturn’s north pole, and embedded within a strong eastward zonal jet at about 78°N planetocentric latitude. Research teams affiliated with University of California, Berkeley, University of Colorado Boulder, Princeton University, University of Chicago, and Brown University have measured wind speeds up to ~120 meters per second along the hexagon’s edges using cloud-tracking algorithms developed at Jet Propulsion Laboratory and NASA Goddard Space Flight Center. The structure displays a coherent Rossby wave-like meandering of the jet, studied using theoretical frameworks from researchers at Imperial College London, University of Cambridge, National Center for Atmospheric Research, and Scripps Institution of Oceanography. The hexagon persists for decades with little longitudinal drift relative to Saturn’s rotation, prompting analyses by teams at Max Planck Institute for Solar System Research, University of Leicester, University of Oxford, and University of California, Los Angeles. Vertical structure inferred from thermal infrared and microwave sounding by groups at California Institute of Technology and Jet Propulsion Laboratory indicates confinement to the troposphere with possible coupling to stratospheric vortices examined by Northwestern University and University of Michigan researchers.
Formation theories invoke barotropic instabilities, shear-driven jet instabilities, trapped Rossby waves, and polar vortex interactions, debated among scientists at Massachusetts Institute of Technology, University of Arizona, University of Texas at Austin, Columbia University, and Yale University. Numerical studies by teams at Princeton University, Imperial College London, Max Planck Institute for Meteorology, and Los Alamos National Laboratory explore how differential rotation and latitudinal potential vorticity gradients can yield polygonal patterns. Laboratory analogs and shallow-water models developed at University of Oxford, University of Cambridge, University of Southampton, and University of Reading replicate hexagonal modes under constrained boundary conditions. Alternative suggestions involving deep-seated convective plumes and interactions with internal heat flux have been pursued by groups at California Institute of Technology, Jet Propulsion Laboratory, Institute for Advanced Study, and University of Tokyo. Debate continues with contributions from Royal Society fellows and members of the American Geophysical Union.
Polygonal and jet-related features appear in other contexts: the polar vortices on Earth, the north polar vortex on Venus, the hexagon-like structures in laboratory rotating fluids studied by researchers connected to ETH Zurich and University of Maryland, and transient jet meanders on Jupiter observed by Galileo (spacecraft), Juno (spacecraft), and ground-based campaigns associated with Space Telescope Science Institute. Studies comparing Saturn and Jupiter polar dynamics have been undertaken at NASA Jet Propulsion Laboratory, European Space Agency, Russian Academy of Sciences, and Chinese Academy of Sciences. The hexagon’s apparent uniqueness among the gas giants has driven comparative work involving Uranus and Neptune atmospheric modeling teams at University of Oxford and University of Arizona.
Numerical models reproducing polygonal jets have been developed by groups at Princeton University, California Institute of Technology, University of Cambridge, Max Planck Institute for Meteorology, and University of Colorado Boulder using shallow-water, primitive-equation, and three-dimensional general circulation models. Laboratory experiments conducted by researchers at École Polytechnique Fédérale de Lausanne, University of Leeds, University of Cambridge, MIT, and University of Southampton employ rotating annulus setups and nonlinear wave forcing to generate stable polygonal flows. Computational efforts leveraging resources at National Center for Supercomputing Applications, Oak Ridge National Laboratory, NERSC, and Leibniz-Rechenzentrum have tested parameter regimes relevant to Saturn’s atmospheric stratification and radiative forcing, with collaborations across European Space Agency and NASA Ames Research Center. Continued progress depends on proposals for future missions and instrument suites endorsed by panels from National Academies of Sciences, Engineering, and Medicine and review committees at NASA and ESA.