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

Future Directions for Investigations and Measurements
The chemical and physical properties of uranian and neptunian ring particles remain almost
completely unknown, beyond the former’s very low albedo. Observing the rings of Uranus and Neptune
at close range in the near infrared would considerably enhance our understanding of their origin and
composition. Observations at high phase angles inaccessible from Earth are the key to estimating particle
sizes. Ground-based observations have detected changes in the rings of Neptune and the diffuse rings of
Uranus on decadal timescales or shorter; Cassini likewise saw significant structural changes in Saturn’s D
and F rings on similar timescales. The mechanisms behind these changes remain mysterious, and it is
highly desirable to study these changing structures in detail. Therefore, orbiter missions to Uranus and/or
Neptune represent the highest priority for furthering ring science in the next decade. 52
The recent New Horizons flyby has demonstrated the value of continued observations of Jupiter’s
rings, revealing a new structure that still is not fully understood. Missions to Jupiter, as well as any
mission encountering Jupiter en route to another target, should observe this poorly characterized ring
system as opportunities allow. 53
The Cassini Solstice mission will continue to yield significant ring science, as articulated above.
In future decades, a dedicated Saturn Ring Observer could potentially obtain “in situ” Saturn-ring data
with unprecedented spatial resolution and temporal coverage. Initial engineering studies for such a
mission exist, but further technology development is required during the next decade to develop a robust
mission profile. 54
Nearly all constituent ring particles are too small to observe individually, even from an orbiting
spacecraft, so a proper interpretation of any observations requires an understanding of their collective
effects and behavior. Thus, for example, theoretical and numerical analyses of ring dynamics are
essential to interpreting the photometry of Saturn’s rings as observed by Cassini and from Earth-based
telescopes. Laboratory studies of potential ring-forming materials also are needed to understand ring
spectroscopy. 55
FIGURE 7.6 In this image of Saturn taken by the Cassini spacecraft of the Saturn system backlit by the
Sun, tiny Earth glints though the magnificent ring system at about the 10 o’clock position. SOURCE:
NASA/JPL/Space Science Institute.
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