The Origin and Evolution of the Solar System

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16 The structure of the Solar SystemFigure 1.8. Three successive alignments of the three inner Galilean satellites which forma Laplacian triplet. Orbits and Jupiter are drawn to scale but angles are exaggerated.Table 1.5. Titius-Bode type relationship compared with the actual semi-major axes for theGalilean satellites. Distances are in units of the Jupiter radius.1 2 3 4SatelliteAmalthea Io Europa Ganymede Callisto 2.5 5.9 9.4 15.0 26.4 Ò 3 6 9 15 27Òtable 1.5. Similar relationships may be constructed for the other major planetsystems.It is easy perhaps to overstate the similarities between the major satellitesystems and the planetary system itself. One property of the planetary systemthat is not mirrored in the satellite systems is the ratio of angular momentum forthe primary spin to that contained in the secondary orbits. As we have seen earlierthe total magnitude of the orbital angular momentum of the major planets is morethan 200 times that of the solar spin. By contrast, the spin of Jupiter has angularmomentum 100 times that of the orbital value for the Galileans. Two major factorscontribute to this difference.
Satellite systems, rings and planetary spins 17(1) The major planets are 200 times more distant from the Sun in terms ofprimary radius. Thus the Galileans orbit Jupiter at 5.9–26.4 Jovian radiiwhereas the major planets orbit the Sun at between 1120 and 6470 solarradii.(2) Jupiter rotates very rapidly compared to the Sun; its angular rate is 60 timesgreater.The mass ratios in the two systems are more similar being 600:1 for the Sun–planets and 4000:1 for Jupiter–Galileans. The other satellite systems have similarratios.None of the other satellites of Jupiter is comparable to the Galileans, the nextlargest being Amalthea, an irregularly shaped body with dimensions ¾¼ Ñ ¢½¼ Ñ ¢ ½¼ km. Two groups of outer satellites, one in direct and the otherin retrograde orbits (inclinations greater than ¼ Æ —see table 1.4), are probablycaptured debris from some event in the vicinity of Jupiter.The Galilean satellites are remarkable for the diversity of their surface structures.Io was the first body, other than the Earth, to show volcanic activity. Justbefore Voyager 1 reached the Jovian system it was predicted that volcanoes shouldbe active on Io (Peale et al 1979) and, indeed, a volcanic plume was imaged bythe approaching spacecraft. Altogether eight volcanoes have been observed onthe satellite. The basis of the prediction was the 2:1 ratio of the periods of Io andEuropa. Because of this the nearest approach, and hence the maximum perturbation,of Io by Europa is always at the same point of Io’s orbit. Thus Io’s orbit isnot quite circular ( ¼¼¼¼½) and because of its proximity to Jupiter it undergoesa periodic tidal stress. Hysteresis converts some of the energy involved inthis alternating stretching and compression into heat and it is estimated that theresultant energy generation in Io amounts to about ½¼ ½¿ W. It is this energy thatdrives the volcanism. The orange-yellow colour of much of Io’s surface is dueto sulphur and sulphur dioxide emission from the volcanoes. Since the surface isconstantly being renewed there is no evidence of bombardment of the surface.Europa, the next Galilean satellite, has a very different appearance. Its densityis a little less than that of the Moon and it is the only Galilean satellite lessmassive than the Moon. The surface is extremely smooth, again showing littleevidence of bombardment damage and indicating an active surface. It is coveredwith ice, which cannot be very thick if the density is taken into account. It isthought that water, in liquid form just below the surface of Europa, is occasionallyreleased and then freezes, covering any underlying surface features. Although itis further from Jupiter than Io it may also have an input of tidal energy. This couldcontribute to the heat required to produce the liquid water. At the same time thetidal flexing could also give rise to the very distinctive cracked surface of Europa.Ganymede, the next satellite outwards, is larger than Mercury and the largestand most massive satellite in the Solar System, having twice the mass of theMoon. It has an icy surface layer, perhaps 100 km thick, below which there isa much thicker layer of water or mushy ice. Older well-cratered regions are dark
Page 1 and 2: The Origin and Evolution of the Sol
Page 5 and 6: ContentsIntroductionxvPART 1The gen
Page 7 and 8: ContentsixPART 2Setting the theoret
Page 9 and 10: Contentsxi7.3 Angular momentum 2257
Page 11: ContentsxiiiPART 4The current state
Page 14 and 15: xviIntroductionwhich they provide a
Page 16 and 17: 4 The structure of the Solar System
Page 23 and 24: Planetary structure 11Figure 1.4. T
Page 25 and 26: Planetary structure 13Figure 1.5. S
Page 27: Satellite systems, rings and planet
Page 31 and 32: Satellite systems, rings and planet
Page 43 and 44: Asteroids 31a precise estimate of t
Page 45 and 46: Asteroids 33Figure 1.17. A schemati
Page 47 and 48: Meteorites 35for in this way. Other
Page 49 and 50: Meteorites 37types of meteorites th
Page 51 and 52: Meteorites 39Figure 1.21. An etched
Page 53 and 54: Comets 41these anomalies contain a
Page 55 and 56: Comets 43Figure 1.23. The structure
Page 57 and 58: Comets 45of the Solar System indica
Page 59 and 60: Stars and stellar evolution 47Figur
Page 71 and 72: The formation of dense interstellar
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The formation of dense interstellar
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The evolution of proto-stars 73Figu
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Observations of star formation 75Be
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Observation of young stars 77Figure
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Theories of star formation 79Figure
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Theories of star formation 81small
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Theories of star formation 83and su
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Planets around other stars 95(a)(b)
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Planets around other stars 97Figure
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Circumstellar discs 99e.g. Vega, ha
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The nature of scientific theories 1
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3.2 Required features of theoriesRe
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Required features of theories 105to
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Required features of theories 107Th
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Chapter 4Theories up to 19604.1 The
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The historical background 113Figure
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The historical background 115Figure
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Buffon’s comet theory 117writing
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The Laplace nebula theory 119Figure
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The Roche model 1214.4 The Roche mo
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The Roche model 123Figure 4.7. A sa
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The Chamberlin and Moulton planetes
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The Jeans tidal theory 127(i) stell
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The Jeans tidal theory 129Figure 4.
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y ×The Jeans tidal theory 131(4.
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The Schmidt-Lyttleton accretion the
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The Schmidt-Lyttleton accretion the
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The major problems revealed 137were
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The major problems revealed 139suma
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Chapter 5A brief survey of modern t
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The Proto-planet Theory 145their ra
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The Capture Theory 147Figure 5.3. T
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The Solar Nebula Theory 1495.4 The
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The Modern Laplacian Theory 151(iii
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The Modern Laplacian Theory 153Figu
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5.6 Analysing the modern theoriesAn
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Formation of the Sun: dualistic the
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Formation of the Sun: monistic theo
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Formation of the Sun: monistic theo
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andFormation of the Sun: monistic t
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Formation of planets 169but, of cou
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Formation of planets 171been brough
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Formation of planets 173Figure 6.5.
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Formation of planets 175Figure 6.8.
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Formation of planets 177Figure 6.10
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Formation of planets 179Table 6.3.
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Formation of planets 185within whic
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Formation of planets 187Table 6.4.
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and the time-scale for the formatio
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Formation of planets 193the main ne
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Formation of satellites 1956.5 Form
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Formation of satellites 197Figure 6
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Formation of satellites 203field pe
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Successes and remaining problems of
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Successes and remaining problems of
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Chapter 7Planetary orbits and angul
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The evolution of planetary orbits 2
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Initial planetary orbits 221Figure
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Initial planetary orbits 223Table 7
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Angular momentum 225Figure 7.9. Var
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Angular momentum 227it is not possi
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The spin axes of the Sun and the pl
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Chapter 8A planetary collision8.1 I
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Interactions between proto-planets
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The Earth and Venus 245being subjec
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The Earth and Venus 247Figure 8.6.
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The Earth and Venus 249Table 8.3. P
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Chapter 9The Moon9.1 The origin of
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The origin of the Earth-Moon system
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The chemistry of the Earth and the
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The chemistry of the Earth and the
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The physical structure of the Moon
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Lunar magnetism 283Figure 9.19. The
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Lunar magnetism 285isted. Another i
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Lunar magnetism 289much smaller tha
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Summary 293The maximum magnetizing
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Mars 295of regular satellites since
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Mars 297Figure 10.1. The densities
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Mars 299Figure 10.2. The structure
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Mars 301Figure 10.4. A model for Ma
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A general description of Mercury 30
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A general description of Mercury 30
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Neptune, Pluto and Triton 307Table
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Neptune, Pluto and Triton 309Table
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Neptune, Pluto and Triton 311where
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Irregular satellites 313It could be
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Summary 315sumed to be close in to
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Meteorites 317and Dodd 1973). This
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Meteorites 319Table 11.1. Percentag
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Meteorites 32111.2.1.2 AchondritesA
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Stony irons 323(a)(b)Figure 11.1. (
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Information from meteorites 325Figu
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Isotopic anomalies in meteorites 32
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Explanations of isotopic anomalies
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Comets—a general survey 355Figure
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Comets—a general survey 357popula
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Comets—a general survey 361the ra
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The inner-cloud scenario 365to have
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Comets from the planetary collision
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Ideas about the origin and features
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374 Comparisons of the main theorie
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Appendix IThe Chandrasekhar limit,
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388 The Chandrasekhar limit, neutro
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390 The Chandrasekhar limit, neutro
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392 The Virial TheoremCombining the
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394 Smoothed particle hydrodynamics
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396 Smoothed particle hydrodynamics
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Appendix IVThe Bondi and Hoyle accr
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400 The Bondi and Hoyle accretion m
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ReferencesAarseth S J 1968 Bull. As
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404 ReferencesFreeman J W 1978 The
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406 ReferencesMullis A M 1991 Geoph
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IndexAannestad P A, 61Aarseth S J,
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410 Indexcirculation, 132circumstel
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412 Indexgrain formation, 347-349Gr
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414 Indexlunarbasalt, , 286highland
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416 Indexdiscovery, 7Great Dark Spo
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418 Indexformation, 145, 148, 195-2
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420 IndexVan Flandern T C, 308, 310
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The Origin and Evolution of the Solar System

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