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

EXPLORING THE GIANT PLANET’S ROLES IN PROMOTING
A HABITABLE PLANETARY SYSTEM
The solar system contains myriad objects—small and large—orbiting the Sun, and these bodies
can directly affect the habitability of Earth. For example, large planetary impacts are an ongoing process,
not merely a historical fact. Observations of Jupiter make this very clear; witness the spectacular impact
of D/Shoemaker-Levy 9 with Jupiter in 1994. The effects of the jovian collisions prompted studies of,
and surveys for, potentially hazardous asteroids in near-Earth space. The surprising second collision of a
body with Jupiter in 2009, followed by two more jovian impacts in 2010, underscores the hazards in the
interplanetary environment.
The Sun itself is highly variable, with potentially significant consequences. The explosive release
of stored magnetic energy in the Sun’s atmosphere leads to extremely large solar “storms,” causing
changes in emitted electromagnetic radiation at all energies, ejecting energetic particles, and enhancing
the solar wind at Earth. The most prominent examples of their manifestations include not only natural
spectacles such as auroral displays, but also direct impacts on human activities such as catastrophic
failures of electrical grids and spacecraft hardware. The aurorae of the Jupiter and Saturn provide
important data points in understanding the propagation of these storms across the solar system.
Understanding these solar eruptions, and their propagation to Earth and beyond, plays an important role in
contemporary solar physics and has generated its own field of space weather.
By studying the giant planets in the context of processes that occur throughout the solar system,
we gain a deeper understanding of how those processes play out here on Earth. This is illustrated with
specific examples about energy balance, interactions with the Sun’s magnetic field, and how the surfaces
in giant planet systems are “weathered.”
Specific objectives associated with the goal of exploring the giant planets’ role in crafting a
habitable planetary system include the following:
• Search for chemical evidence of planetary migration;
• Explore the giant planets’ role in creating our habitable Earth via large impacts; and
• Determine the role of surface modification via smaller impacts.
Subsequent sections examine each of these objectives in turn, identifies important questions to be
addressed and future investigations and measurements that could provide answers.
Search for Chemical Evidence of Planetary Migration
In the past, various models have been proposed for formation of planetary systems in general and
specifically for the solar system. All these models made basic assumptions concerning condensation of
planet-forming components and the manner in which they were accumulated by the planets. In the last
two decades, increased computing power has led to rejection of some models and increased support for a
model in which Jupiter and Saturn interacted to perturb the planets into their current configuration. The
degree to which the planets were formed by collisional impacts of volatile-bearing bodies or collapse of
gases onto larger bodies should have left behind evidence that can be found within the compositional
makeup of the surviving bodies. Thus, determination of the chemical composition (D/H, other isotopic
abundances, noble gases, water) will discriminate among models that will constrain initial conditions and
illuminate how the planets have evolved.
The distribution of the heavy elements (atomic mass >4) as a function of distance from the Sun
can provide strong constraints for discriminating among theories and dynamical models of solar system
formation and evolution. One of the predictions of the models is that the central core mass of the giant
planets should increase with distance from the Sun. This should result in a corresponding increase in the
abundances of the heavier elements. Currently the only element measured for all four planets is carbon,
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