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

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8 Satellites: Active Worlds and Extreme Environments This chapter is devoted to the major satellites of the giant planets: those large enough to have acquired a roughly spherical shape through self-gravity. There are 17 of these worlds (four at Jupiter, seven at Saturn, five at Uranus, and one at Neptune), ranging in diameter from 5260 kilometers (Ganymede) to 400 kilometers (Mimas) (Table 8.1, Figure 8.1). They are astonishingly diverse, with surface ages spanning more than 4 orders of magnitude, and surface materials ranging from molten silicate lava to nitrogen frost. This diversity makes the satellites exceptionally interesting scientifically, illuminating the many evolutionary paths that planetary bodies can follow as a function of their size, composition, and available energy sources, and allowing us to investigate and understand an exceptional variety of planetary processes. However, this diversity also presents a challenge for any attempt to prioritize exploration of these worlds, as we move from initial reconnaissance to focused in-depth studies. The sizes, masses, and orbits of all the large satellites are now well known, and are key constraints on the origin of the planetary systems to which they belong. Additional constraints come from their detailed compositions, which we are just beginning to investigate. Several worlds have unique stories to tell us about the evolution of habitable worlds, by illuminating tidal heating mechanisms, providing planetary-scale laboratories for the evolution of organic compounds, and by harboring potentially habitable subsurface environments. Many of these worlds feature active planetary processes that are important for understanding both these bodies themselves, and worlds throughout the solar system. These processes include silicate volcanism, ice tectonics, impacts, atmospheric escape, chemistry, and dynamics, and magnetospheric processes. While much can still be learned from ground-based and near-Earth telescopic observations, particularly in the temporal domain, and from analysis of existing data, missions to these worlds are required to produce new breakthroughs in our understanding. During the past decade, our understanding of these worlds has been substantially expanded by the Cassini spacecraft and its Huygens probe that descended to Titan in 2005. Data from Cassini continues to revise and expand what we know about Saturn’s moons. In addition, continued analysis from past missions such as Galileo has produced surprises as well as helping inform the planning for future missions. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 8-1
TABLE 8.1 Characteristics of the Large- and Medium-Size Satellites of the Giant Planets Primary Satellite Distance from Primary (km) Radius (km) Bulk Density (g cm -3 ) Geometric Albedo Dominant Surface Composition Surface Atmospheric Pressure (bars) Dominant Atmospheric Composition Notes Jupiter Io 422,000 1822 3.53 0.6 S, SO2, silicates 10 -9 SO2 Intense tidally driven volcanism, plumes, high mountains Europa 671,000 1561 3.01 0.7 H2O, hydrates 10 -12 O2 Recent complex resurfacing, probable subsurface ocean Ganymede 1,070,000 2631 1.94 0.4 H2O, hydrates 10 -12 O2 Magnetic field, ancient tectonism, probable subsurface ocean Callisto 1,883,000 2410 1.83 0.2 Phylosilicates?, H2O Partially undifferentiated, heavily cratered, probable subsurface ocean Saturn Mimas 186,000 198 1.15 0.6 H2O Heavily cratered Enceladus 238,000 252 1.61 1.0 H2O Intense recent tectonism, active water vapor/ice jets Tethys 295,000 533 0.97 0.8 H2O Heavily cratered, fractures Dione 377,000 562 1.48 0.6 H2O Limited resurfacing, fractures Rhea 527,000 764 1.23 0.6 H2O Heavily cratered, fractures Titan 1,222,000 2576 1.88 0.2 H2O, organics, liquid CH4 1.5 N2, CH4 Active hydrocarbon hydrological cycle, complex organic chemistry Iapetus 3,561,000 736 1.08 0.3 H2O, organics? Heavily cratered, extreme albedo dichotomy Uranus Miranda 130,000 236 1.21 0.3 H2O Complex and inhomogeneous resurfacing Ariel 191,000 579 1.59 0.4 H2O Limited resurfacing, fractures Umbriel 266,000 585 1.46 0.2 H2O, dark material Heavily cratered Titania 436,000 789 1.66 0.3 H2O Limited resurfacing, fractures Oberon 584,000 761 1.56 0.2 H2O, dark material Limited resurfacing Neptune Triton 355,000 1353 2.06 0.8 N2, CH4, H2O 10 -5 N2, CH4 Captured. Recent resurfacing, complex geology, active plumes PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION 8-2
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PREPUBLICATION COPY Subject to Furt
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The National Academy of Sciences is
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COMMITTEE ON THE PLANETARY SCIENCE
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STAFF DAVID H. SMITH, Senior Progra
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Preface Strategic planning activiti
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statement of task’s call for “i
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Understand the Processes That Contr
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Executive Summary In recent years,
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however, that the Discovery program
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• Jupiter Europa Orbiter (descope
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TABLE ES.2 Medium Class Missions—
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Summary This report was requested b
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• Recent volcanic activity on Ven
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Mission Study Process and Technical
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Near the end of the past decade, NA
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• Mars Astrobiology Explorer-Cach
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development, and descoped or cancel
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Plausible circumstances could impro
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Data Distribution and Archiving Dat
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Sample curation facilities are crit
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consider making equivalent systems
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committee concluded that for the mo
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alanced ground-based solar astronom
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1 Introduction to Planetary Science
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THE 2002 SOLAR SYSTEM EXPLORATION D
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Medium The first decadal survey ide
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FIGURE 1.6 Victoria crater as image
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FIGURE 1.8 The mirror for the Large
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FIGURE 1.10 From a comet, to the de
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• The committee’s programmatic
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• Opportunities for joint venture
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FIGURE 1.14 Schematic showing the f
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2 National and International Progra
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FIGURE 2.3 Sand dunes on Mars photo
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NASA’s Earth Science Division Pla
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More recently, among the goals of t
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FIGURE 2.6 A natural bridge on the
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investigations should still be deve
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FIGURE 2.10 The surface of Titan as
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3 Shared objectives that incorporat
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3 Priority Questions in Planetary S
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• How have the myriad chemical an
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How Did the Giant Planets and Their
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heavy bombardment? Clues to address
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Did Mars or Venus Host Ancient Aque
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We lack critical geophysical data a
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detected in time. The report conclu
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How Have the Myriad of Chemical and
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13. P.R. Estrada, I. Mosqueira, J.J
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51. M.J. Mumma, G.L. Villanueva, R.
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4 The Primitive Bodies: Building Bl
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FIGURE 4.1 Asteroids and comet nucl
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• How do the compositions of pres
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Future Directions for Investigation
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Astrobiology is the study of the or
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Important Questions Some important
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observations of the outer parts of
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Sample Curation and Laboratory Faci
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In the previous decadal survey, CCS
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asteroid (either ice-rock or metal-
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hazard. Asteroid 433 Eros, one of t
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BOX 4.1 The Discovery Program, Vita
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ody exploration can be achieved by
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34. H.H. Hsieh and D. Jewitt. 2006.
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FIGURE 5.1 Mercury, Venus, and the
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Constrain the Bulk Composition of t
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from Venus Express and Galileo may
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• Understand the composition and
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• Is there evidence of environmen
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Important Questions Some important
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timescales, including the possible
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that may have fostered life, there
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• Venus In Situ Explorer • Sout
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FIGURE 5.3 Venus’s climate is con
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Important scientific objectives tha
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BOX 5.1 Planetary Roadmaps Roadmaps
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4. D.J. Lawrence, W.C. Feldman, J.O
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6 Mars: Evolution of an Earth-like
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BOX 6.1 Mars Science Laboratory Sch
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live there now?”—both key compo
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characteristics (water, gradients i
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availability, physicochemical facto
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UNDERSTAND THE PROCESSES AND HISTOR
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FIGURE 6.4 Examples of recent clima
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particularly the polar-layered depo
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FIGURE 6.6 Geologic time sequence o
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Future Directions for Investigation
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planets and for understanding subse
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experiments, compounded by the unce
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Curation Martian samples require sc
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particle sizes, wavelength ranges,
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environmental conditions including
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Mars Polar Climate Mission As a fol
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R.E. Arvidson, C.C. Allen, D.J. Des
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Page 191 and 192: B.M. Jakosky and R.J. Phillips. 200
Page 193 and 194: 72. White papers received by decada
Page 195 and 196: (MRR-SAG). Posted by the Mars Explo
Page 197 and 198: the solar system formed. Understand
Page 199 and 200: FIGURE 7.2 Left: This Hubble image
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Page 203 and 204: FIGURE 7.4 The intrinsic specific l
Page 205 and 206: Investigate the Chemistry of Giant
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Page 209 and 210: • What causes the enormous differ
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Page 217 and 218: • Assess tidal evolution within g
Page 219 and 220: • What processes drive the visibl
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Page 223 and 224: INTERCONNECTIONS Links to Other Par
Page 225 and 226: SUPPORTING RESEARCH AND RELATED ACT
Page 227 and 228: FIGURE 7.10 Our atmosphere blocks l
Page 229 and 230: Cassini Solstice Mission ADVANCING
Page 231 and 232: 8. Determine the composition, struc
Page 233 and 234: Summary To achieve the primary goal
Page 235 and 236: Outer Solar System; William B. McKi
Page 237 and 238: 54. White papers received by decada
Page 239: 92. White papers received by decada
Page 243 and 244: organisms live there now?” Titan
Page 245 and 246: • Why are Titan and Callisto appa
Page 247 and 248: Callisto but unlike Ganymede. This
Page 249 and 250: valuable window into solar system h
Page 251 and 252: Future Directions for Investigation
Page 253 and 254: FIGURE 8.6 Multiple jets, dominated
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Page 265 and 266: hardened technology for Io and Gany
Page 267 and 268: FIGURE 8.11 After a comprehensive t
Page 269 and 270: FIGURE 8.12 Galileo color image of
Page 271 and 272: Titan Saturn System Mission Many Ti
Page 273 and 274: 1. What is the nature of Enceladus
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Page 277 and 278: 7. O. Mousis, J.I. Lunine, M. Pasek
Page 279 and 280: 45. K.K. Khurana, M.G. Kivelson, K.
Page 281 and 282: 9 Recommended Flight Investigations
Page 283 and 284: All of the recommendations below ar
Page 285 and 286: As discussed in more detail below,
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Page 289 and 290: TABLE 9.2 Discovery Program Mission
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overarching questions in Chapter 3.
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These five were selected from the s
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The Mars community, in their inputs
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should immediately undertake an eff
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(a) (b) FIGURE 9.1 Notional funding
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As noted, the recommended and cost-
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described above are the existing De
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The projected need decreased from 2
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partnership with the Department of
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10 Planetary Science Research and I
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Through the direct involvement of s
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Theoretical development and numeric
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Defining the Need Jon Miller, in hi
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efforts, can help assure compatibil
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history. And telescopic observation
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Hubble Space Telescope Hubble obser
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Although Ka-band downlink has a cle
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and Planetary Institute. Currently,
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the Green Bank Telescope (GBT), and
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up observations. Likewise, monitori
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11 The Role of Technology Developme
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particular technology item. In gene
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The Requirement for Power Of all th
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proposals and populated by technolo
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TABLE 11.1 Summary of Types of Miss
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Solar System Access and Other Core
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influence on the planetary science
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A Letter of Request and Statement o
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latter topics are treated in the NR
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main findings and recommendations s
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TABLE B.1 Institutional Distributio
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M. Gudipati, Laboratory Studies for
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Scott A. Sandford, The Comet Coma R
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C Cost and Technical Evaluation of
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were all full mission studies selec
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Schedule To aid in the assessment o
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FIGURE C.3 Complexity Based Risk As
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Lunar Lander Network⎯Four Landers
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Caching Mars Rover Mars Astrobiolog
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Mars Sample Return Lander and Mars
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Flagship‐class Europa Orbiter SOU
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Saturn Atmospheric Entry Probe SOUR
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Enceladus Orbiter Spacecraft SOURCE
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Uranus Orbiter with Entry Probe SOU
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SUMMARY Linked technical, cost, and
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Overview The purpose of this rapid
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Conclusions Based on analyses of th
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Technology development was found to
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• Characterize the local meteorol
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• Characterize Ganymede’s uniqu
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landing in the small southern lakes
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atmospheric probe and another a sep
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FIGURE E.1 Projected budget for the
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Biosphere: The life zone of Earth o
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EPOXI: The name of the extended mis
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Late heavy bombardment: A postulate
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Nili Fossae region: A fracture in t
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Protoplanet: A planet in the proces
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Stardust: A spacecraft launched in
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G Mission and Technology Study Repo
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