Vision and Voyages for Planetary Science in the - Solar System ...

• What processes drive the visible atmospheric flow and how do they couple to the interior
structure and deep circulation?
• What are the sources of vertically propagating waves that drive upper atmosphere oscillations
and do they play a role on all planets?
• Are there similar processes on Uranus and Neptune, and how do all these compare with
Earth’s own stratospheric wind, temperature and related abundance (ozone, water) variations?
• How does moist convection shape tropospheric stratification?
• What are the natures of periodic outbursts such as the global upheaval on Jupiter and the
infrequent great white spots on Saturn?
Future Directions for Investigations and Measurements
To answer these, we must resolve the three-dimensional structure of the atmospheric flow fields
with high spatial and temporal resolution, including polar regions. The vertical motions in the troposphere
involve the fast, localized, motions caused by moist convection and the slow, global, overturning
meridional circulation caused by the predicted (Hadley-like) belt-zone convection cells.
Determining atmospheric motion and coupling includes the study of atmospheric waves, and the
stratospheric responses to the wave forcing (oscillations); such waves may have a chemical signature.
The stratospheric oscillations that have been discovered on Earth, Mars, Jupiter and Saturn provide a rare
stage for conducting comparative planetological investigation between terrestrial and giant planets. It may
also be possible to detect similar oscillations on Uranus and Neptune.
Finally, there is a need to explore polar phenomena. Jupiter’s poles exhibit numerous small
vortices, and, to date, their zonal mean flow structure has not been observed in detail. Saturn’s north pole
has a circumpolar jet that meanders in a hexagonal shape, while the south pole has a hurricane-like
structure with a well defined eye-wall. Little is known about the polar regions of Uranus and Neptune.
Some of the above atmospheric objectives may be addressed by Juno and JEO for Jupiter, and to
some extent by Cassini for Saturn. Significant advances on Jupiter by JEO would require long temporal
observations, adequate spatial resolution on Jupiter, and relevant instrumentation. For Uranus or
Neptune, these atmospheric objectives are poorly constrained by Earth-based data. An orbiter would be
optimal for investigating such phenomena. Significant theoretical and modeling research should also be
supported to infer the atmospheric structures underlying the observed layers and to advance the
understanding of shear instabilities. 77
Juno may achieve measurements of gravitational signatures of deep zonal flows for Jupiter, and
the Cassini mission may do likewise for Saturn during its final proximal orbits. This will reveal the basic
structure of the deep flow driven by internal convection, and yield information about the internal heat
transport. Juno and Cassini should place useful limits on the higher-order moments of the internal
magnetic fields and potentially detect some temporal evolution (i.e., secular variation). For an ice giant, a
flyby could moderately improve our understanding, while an orbiter with a low periapse approach would
greatly advance the scientific understanding of the interiors and magnetic fields of the ice giants. 78
Assess Tidal Evolution Within Giant Planet Systems
A ubiquitous example of an external process within planet systems is the tide raised on a planet
by an inner satellite, and the resulting transfer of angular momentum from the planet’s spin to the orbit of
the moon (or vice versa in the case of retrograde or sub-synchronous satellites such as Triton and
Phobos). Such tidal torques are thought to have established the orbital architectures of the inner satellite
systems of Jupiter, Saturn and Uranus—including their numerous orbital resonances—as well as the
current states of the Earth-Moon and Pluto-Charon systems. Tides raised by giant planets on their
satellites, in concert with eccentricities driven by orbital resonances, are responsible for significant
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