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

TABLE 7.1 Major Accomplishments by Ground- and Space-based Studies of Giant Planets in the Past
Decade
Major Accomplishment
The census of known exoplanets increased dramatically, from about 50 in 2000 to more than
500 in 2011, with an additional 1,200 candidates as of this writing a ; most of these are giants,
with increasing evidence that ice-giant-sized planets are more abundant than Jupiters; first
compositional measurements acquired; and complex multi-planet systems discovered.
A spacecraft en route to Pluto observed Jupiter’s polar lightning, the life cycle of fresh
ammonia clouds, the velocity of extensive atmospheric waves, boulder-size clumps speeding
through the planet’s faint rings, and the path of charged particles in the previously
unexplored length of the planet’s long magnetic tail.
Discoveries at Saturn include confirmation of the hot southern polar vortex, deep lightning,
large equatorial wind changes and seasonal effects, ring sources and shepherd moons,
propeller-like ring structures as well as spokes and wakes, and the likely source of Saturn’s
kilometric radio emissions
Uranus’s equinox in 2007 was observed with modern instruments (last equinox was in
1965). Revealing unprecedented cloud activity with both bright and dark atmospheric
features, two new brightly colored rings, and several new small moons.
Neptune’s ring arcs shifted location and brightness in an unexplained fashion, and evidence
emerged for a hot polar vortex on Neptune.
Three giant impacts on Jupiter have been recorded since June 2009; one of them was large
enough to create a debris field the size of the Pacific Ocean; Jupiter also exhibited planetwide
cloud and color changes for the first time in two decades.
Mission and/or
Technique
Ground- and spacebased
telescopes
New Horizons
Cassini
Ground-based
telescopes
Ground-based
telescopes
Ground-based
telescopes
a W. Borucki and the Kepler Team, Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four
months of data, submitted to Astrophysical Journal, arXiv:1102.0541 [astro-ph.EP], 2011.
Currently, Earth is the single known example of an inhabited world, and the solar system’s giants
hold clues to how Earth came to be. Bearing this in mind, we articulate three overarching goals for giant
planet system exploration, each of which is discussed in more depth in subsequent sections.
• Giant planets as ground truth for exoplanets: Explore the processes and properties that
influence giant planets in the solar system (including formation, orbital evolution, migration,
composition, atmospheric structure, and environment), in order to characterize and understand the
observable planets in other planetary systems.
• Giant planets role in promoting a habitable planetary system: Test the hypothesis that the
existence, location, and migration of the giant planets in the solar system has contributed directly to the
evolution of terrestrial planets in the habitable zone.
• Giant planets as laboratories for properties and processes on Earth: Establish the relevance of
observable giant planet processes and activities, such as mesoscale waves, forced stratospheric
oscillations, and vortex stability, as an aid to understanding similar processes and activities on Earth and
other planets.
PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION
7-3