1B11 Foundations of Astronomy The Jovian Planets Silvia Zane, Liz Puchnarewicz

1B11 The Giant Planets + the icy object Pluto Low densities  mostly H & He (ices for Uranus, Neptune) “Surfaces” : cloud tops Magnetic fields: all strong (Jupiter’s mag. Moment 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.. The 4 “giants”

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

1B11 The Interior Ex. Uranus and Neptune Ices (H 2 0, CH 4 ) H 2 0 (+ He) Rocky core? Same size as rock/ice core of Jupiter and Saturn 30% (Radius) 75% 100%

1B11 The Interior Hydrogen Phase diagram P (Mbar) T(K) Liquid H 2 Solid H 2 Liquid Metallic Solid Metallic J S U, N

1B11 The Surface Layers Predicted Cloud Structure Altitude (km) T(K) These clouds are white. The reds and brown observed clouds result from more complex hydrocarbons produced by photolysis of NH 3, CH 4, etc.. Clouds are more muted on Saturn, owing to lower UV bar 1 bar 10 bar NH 3 NH 4 SH H2OH2O

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.

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…

1B11 Planetary rings 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 RPRP R Moonlet, held together by gravity Disrupted by tidal forces

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

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

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

1B11 Titan (moon of Saturn) Atmospheric composition: N 2 : 82 –99% CH 4 : 1-6 % Ar: 1-6%  Many Hydrocarbon traces, e.g. Ethane (C 2 H 6 ) Clouds: organic molecules produced by photolysis Surface: ice? Covered in hydrocarbons, possibly liquid?

1B11 Triton (moon of Neptune) Composition: Ice/rock? Very thin (10 –5 bar) N 2 and CH 4 atmosphere It has a retrograde orbit  CAPTURED? similar object to Pluto?

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) N 2 with CH 4 (like Triton) Moon: Charon (radius=595 km, orbital period 6.4 d)

1B11 Trans-Neptunian objects (TNOs) Since 1992  200 icy objects with diameters  100 km have been found beyond Neptune. More than 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

1B11 web sites Images of planets, missions, moons, rings.. And links therein!