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From page 285... ... 11 Question 8: Circumplanetary Systems What processes and interactions establish the diverse properties of satellite and ring systems, and how do these systems interact with the host planet and the external environment? Circumplanetary systems -- where a system of moons and/or rings orbit a central body -- are seen throughout the solar system, and in some cases are akin to mini-solar systems with numerous and varied orbiting bodies (Figure 11-1) Read the entire page →
From page 286... ... 286 ORIGINS, WORLDS, AND LIFE FIGURE 11-1 A selection of circumplanetary systems of the solar system. Distances are normalized to the size of each primary body. Read the entire page →
From page 287... ... QUESTION 8: CIRCUMPLANETARY SYSTEMS 287 Q8.1 HOW DID CIRCUMPLANETARY SYSTEMS FORM AND EVOLVE OVER TIME TO YIELD DIFFERENT PLANETARY SYSTEMS? The physical, orbital, and compositional characteristics of the present-day circumplanetary material provide clues as to how these systems, and their parent planets, have formed and evolved. Read the entire page →
From page 288... ... 288 ORIGINS, WORLDS, AND LIFE and densities. At present, the combination of factors leading to the various bulk composition patterns observed across the solar system (see Figure 11-1) Read the entire page →
From page 289... ... QUESTION 8: CIRCUMPLANETARY SYSTEMS 289 FIGURE 11-2 The inferred interior structures of select moons in the solar system. These structures are subject to uncertainties on material porosity and composition (e.g., metal content and degree of hydration of the silicate rock, impurity content in the ice, abundance of refractory organic material of intermediate density, relative thicknesses of oceans and ice shells) Read the entire page →
From page 290... ... 290 ORIGINS, WORLDS, AND LIFE Strategic Research for Q8.1 • Determine the differentiation state, radial interior structure, tidal response, and presence/absence of water and magma oceans and reservoirs within the moons of Jupiter, Saturn, Uranus, and Neptune by measuring their gravity fields, shape, induced magnetic field and plasma environment, and other geophysical quantities. • Determine the masses, densities, and bulk compositions of Kuiper belt objects and their satellites with surveys for multiple systems and satellites, and characterization of their bulk properties and orbital motion. Read the entire page →
From page 291... ... QUESTION 8: CIRCUMPLANETARY SYSTEMS 291 FIGURE 11-3 Schematic illustration of the interior structures and proposed processes responsible for the transport of heat and material through planetary satellites -- focusing on Io, Europa, Enceladus, and Titan. While these worlds represent four well-studied endmembers, similar processes may occur on a variety of planetary satellites across the solar system, including the satellites of Jupiter, Saturn, Uranus, and Neptune. Read the entire page →
From page 292... ... 292 ORIGINS, WORLDS, AND LIFE Matching observations with theoretical predictions for tidal hearing is difficult because of a lack of observational constraints of the interior structures of tidally heated worlds, incomplete theoretical models, and the lack of knowledge of how relevant planetary materials (e.g., both within the rock/ice/melt of the satellite, and within the giant planet cores and fluid envelopes) behave under relevant pressure, temperature, and forcing conditions. Read the entire page →
From page 293... ... QUESTION 8: CIRCUMPLANETARY SYSTEMS 293 bands on Europa, fractures on Enceladus, grooved terrain on Ganymede, wispy terrain on Dione, fractures on Triton, and canyons on Tethys, Miranda, Pluto, and Charon. Tectonic activity from shear stresses is less prevalent but is observed on Io, Europa, Ganymede, and Enceladus in the form of strike-slip faults, deformation within bands, and deformation of existing features (e.g., craters) Read the entire page →
From page 294... ... 294 ORIGINS, WORLDS, AND LIFE insignificant (e.g., Ahuna Mons on Ceres) , or ceased long ago (e.g., Wright and Piccard Montes on Pluto, irregular mare patches on the Moon [see Figure 2-5] Read the entire page →
From page 295... ... QUESTION 8: CIRCUMPLANETARY SYSTEMS 295 Beyond knowing what bodies have dynamos, it is also important to characterize the magnetic fields. Ganymede's intrinsic magnetic field is known to be dipole-dominated, but its detailed configuration and evolution over time have not yet been determined (Journaux et al. Read the entire page →
From page 296... ... 296 ORIGINS, WORLDS, AND LIFE • Determine the rheological behavior of icy crusts, including determining how and when they fracture with laboratory and analogue studies of ice failure and rheological behavior at the conditions relevant to icy satellites. • Determine how, why, and when tectonic and (cryo) Read the entire page →
From page 297... ... QUESTION 8: CIRCUMPLANETARY SYSTEMS 297 FIGURE 11-4 Two satellites of Saturn imaged by Cassini show the extremes of surface crater density. Left: Methone has a smooth surface with no visible impact craters, as it is very small and young. Read the entire page →
From page 298... ... 298 ORIGINS, WORLDS, AND LIFE readily ionized, enabling it to then be carried along magnetic field lines into the atmosphere, as seen on Saturn. Deeper searches at Uranus and Neptune may show new dusty rings. Read the entire page →
From page 299... ... QUESTION 8: CIRCUMPLANETARY SYSTEMS 299 Q8.4 HOW DO PLANETARY MAGNETOSPHERES INTERACT WITH SATELLITES AND RINGS, AND VICE VERSA? The co-rotating charged particles of outer planet magnetospheres interact with the surfaces and atmospheres of the moons and rings embedded in the magnetospheres and erode them. Read the entire page →
From page 300... ... 300 ORIGINS, WORLDS, AND LIFE FIGURE 11-5 Top panel: Saturn's radiation belts as structured by the rings and inner moons, with gaps owing to the absorption of energetic protons by the moons and rings, and with the highest-energy (giga-electron volt [GeV] Read the entire page →
From page 301... ... QUESTION 8: CIRCUMPLANETARY SYSTEMS 301 and morphology of these rings. Similarly, both the prevalence and evolution of the dusty spokes over Saturn's B-ring are clearly influenced by seasonal changes in the magnetospheric environment. Read the entire page →
From page 302... ... 302 ORIGINS, WORLDS, AND LIFE Strategic Research for Q8.4 • Quantify material sources, sinks, and mass transport between Jupiter's magnetosphere and moons via in situ magnetic field and plasma measurements. • Characterize the magnetospheric interactions between Uranus and Neptune's atmosphere, moons, and rings with observations of planetary aurorae, measurements of satellite and ring exospheres and ionospheres, in situ measurements of the global distribution of the plasma composition, density, velocity and temperature, neutral density and composition, and charged dust in both the orbital plane of the moons and rings and at high inclinations. Read the entire page →
From page 303... ... QUESTION 8: CIRCUMPLANETARY SYSTEMS 303 more tenuous ring systems dominated by fine debris released from larger bodies can provide information about dust production, transport, and loss in different environments (Hedman et al. Read the entire page →
From page 304... ... 304 ORIGINS, WORLDS, AND LIFE Q8.5c What Is the Life Cycle of Planetary Rings? Recent measurements of the total mass of Saturn's rings and the mass flux between those rings and the planet indicate that the composition and mass of Saturn's rings may change substantially on timescales of hundreds of millions of years, which is much shorter than the age of the solar system (Waite et al. Read the entire page →
From page 305... ... QUESTION 8: CIRCUMPLANETARY SYSTEMS 305 • Constrain the origin of Phobos and Deimos, including whether they arose from past martian rings, by determining their bulk composition and interior structure by in situ geochemical and geophysical measurements. • Determine whether equatorial ridges on worlds like Iapetus, Pan, and Atlas are produced by the deposition of ancient rings or by other processes, with a combination of high-resolution remote sensing observations of equatorial ridges, and theoretical models for ring collapse and other competing hypotheses. Read the entire page →
From page 306... ... 306 ORIGINS, WORLDS, AND LIFE Crida, A., S Charnoz, H.W. Read the entire page →
From page 307... ... QUESTION 8: CIRCUMPLANETARY SYSTEMS 307 O'Donoghue, J., L Moore, J Read the entire page →
From page 308... ... Q9 PLATE: Earth, viewed from above the Moon's surface by the Lunar Reconnaissance Orbiter in 2015. SOURCE: Courtesy of NASA/GSFC/Arizona State University. Read the entire page →

From page 285...

... 11 Question 8: Circumplanetary Systems What processes and interactions establish the diverse properties of satellite and ring systems, and how do these systems interact with the host planet and the external environment? Circumplanetary systems -- where a system of moons and/or rings orbit a central body -- are seen throughout the solar system, and in some cases are akin to mini-solar systems with numerous and varied orbiting bodies (Figure 11-1)