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1B11 Foundations of Astronomy The Jovian Planets

1B11 Foundations of Astronomy The Jovian Planets. Silvia Zane, Liz Puchnarewicz emp@mssl.ucl.ac.uk www.ucl.ac.uk/webct www.mssl.ucl.ac.uk/. 1B11 The Giant Planets. The 4 “giants”. + the icy object Pluto. Low densities  mostly H & He (ices for Uranus, Neptune) “Surfaces” : cloud tops

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1B11 Foundations of Astronomy The Jovian Planets

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  1. 1B11 Foundations of AstronomyThe Jovian Planets Silvia Zane, Liz Puchnarewicz emp@mssl.ucl.ac.uk www.ucl.ac.uk/webct www.mssl.ucl.ac.uk/

  2. 1B11 The Giant Planets The 4 “giants” + the icy object Pluto • Low densities mostly H & He (ices for Uranus, Neptune) • “Surfaces” : cloud tops • Magnetic fields: all strong (Jupiter’s mag. Moment 20.000 Earth’s) • Internal heat: J, S, N radiate  twice the heat they receive from the Sun  internal heat e.g. gravitational contraction ( 1mm/year), etc..

  3. 1B11 The Interior Ex. Jupiter Based on mean density, assumed chemical composition. And Hydrogen Phase diagram T 165K P 1 bar T10000K P3 Mbar Liquid Molecular H (+ He) T20000K P70 Mbar Liquid Metallic H (+ He) 15% (Radius) 75% 100% ? Rocky-ice core10-15 M Clouds (complex molecules)

  4. 1B11 The Interior Ex. Uranus and Neptune H20 (+ He) Ices (H20 , CH4) 30% (Radius) 75% 100% Rocky core? Same size as rock/ice core of Jupiter and Saturn

  5. 1B11 The Interior Hydrogen Phase diagram T(K) J S 104 Liquid H2 Liquid Metallic U, N 103 Solid H2 Solid Metallic 102 0.1 1.0 10 100 P (Mbar)

  6. Altitude (km) T(K) 1B11 The Surface Layers Predicted Cloud Structure 0.1 bar +50 NH3 1 bar 0 NH4SH -50 H2O 10 bar -100 120 160 340 • These clouds are white. The reds and brown observed clouds result from more complex hydrocarbons produced by photolysis of NH3, CH4, etc.. • Clouds are more muted on Saturn, owing to lower UV

  7. 1B11 The Surface Layers This animation of Jupiter was created from a mosaic of images taken by the Voyager spacecraft. As the animation starts, the great red spot is towards the left side. A number of brown spots can be seen just above center.

  8. 1B11 Internal Heat Jupiter, Saturn and Neptune all radiate about twice as much energy as they receive from the Sun  An internal heat source, possible responsible for dynamic meteorology of Jupiter Possibilities: • Primordial heat • Gravitational Contraction ( 1mm/yr) • Combination of all of these…

  9. 1B11 Planetary rings Moonlet, held together by gravity • All four giant planets have rings • Rings are composed of small, solid (generally icy) particles orbiting in equatorial plane • Probable origin: disruption of small moons or comets within a giant planet’s Roche limit Disrupted by tidal forces R RP

  10. 1B11 Major Satellites of Jupiter and Saturn Jupiter (Galilean Satellites, 1610) Saturn (Titan, 1655)

  11. 1B11 Galilean Satellites: Summary Io: • Highly volcanic • Energy Source: tidal friction Europa: • icy crust, few craters • Evidence for ocean: • recent resurfacing (new ice) • surface features (ice flows) • spectral evidence for salts •  possible biosphere ?

  12. 1B11 Galilean Satellites: Summary Ganimede, Callisto: • Thick icy mantles to keep density low Heavily cratered icy crust (esp. Callisto) Silicate mantle Ice (possibly liquid at depth) Possible core ? (esp. Ganimede) • Both probably now inert, Ganymede has been active more recently than Callisto (few craters  younger surface)

  13. 1B11 Titan (moon of Saturn) Atmospheric composition: N2: 82 –99% CH4: 1-6 % Ar: 1-6% Many Hydrocarbon traces, e.g. Ethane (C2H6) • Clouds: organic molecules produced by photolysis • Surface: ice? Covered in hydrocarbons, possibly liquid?

  14. 1B11 Triton (moon of Neptune) Composition: Ice/rock? Very thin (10–5 bar) N2 and CH4 atmosphere • It has a retrograde orbit  CAPTURED? • similar object to Pluto?

  15. 1B11 Pluto (discovered 1930) • Mean orbital distance: 39.5 AU • Eccentricity: 0.25 • Orbital inclination: 17.1º • Radius : 1150 km (0.18 R : smaller than triton!) • Mean density: 2.0 g cm–3 (rock/ice composition) • Atmosphere: very thin (10–5 bar) N2 with CH4 (like Triton) • Moon: Charon (radius=595 km, orbital period 6.4 d)

  16. 1B11 Trans-Neptunian objects (TNOs) • Since 1992 200 icy objects with diameters 100 km have been found beyond Neptune. • More than 70000 are thought to exist between 30 and 50 AU. • Pluto and Triton are probably just the largest and/or the closest members of the TNO population. • TNOs probably mark the inner edge of the KUIPER belt-source of short period comets

  17. 1B11 web sites http://www.ex.ac.uk/Mirrors/nineplanets http://www.solarviews.com/eng/ Images of planets, missions, moons, rings.. And links therein!

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