Chapter 12-13 Saturn & Uranus and Neptune

12.1 Orbital and Physical Properties

  • Mass: 5.7 × 1026 kg

  • Radius: 60,000km

  • Density: 700kg/m³ —less than water!

  • Rotation: Rapid and differential, enough to flatten Saturn considerably

  • Rings: Very Prominent; wide but extremely thin

  • Saturn’s atmosphere also shows zone and band structure, but coloration is much more subdued than Jupiter’s

  • Mostly molecular hydrogen, helium, methane, and ammonia; helium fraction is much less than on Jupiter

12.3 Saturn’s Interior and Magnetosphere

  • Interior structure similar to Jupiter’s

  • Saturn also has a strong magnetic field, but only 5% as strong as Jupiter’s

12.4 Saturn’s Spectacular Ring System

  • Ring particles range in size from fractions of a millimeter to ten tens of meters

  • Composition: Water ice— similar to snowballs

  • Why rings?

  • Too close to planet for moon to form— tidal forces would tear it apart

  • Voyager probes showed Saturn’s rings to be much more complex than originally thought

  • Details of formation are unknown:

    • Too active to have lasted since birth of solar system

    • Either must be continually replenished, or are the result of catastrophic event

13.1 The Discoveries of Uranus and Neptune

  • Uranus was discovered in 1781 by Herschel; first planet to be discovered in more than 2000 years

  • Little detail can be seen from Earth

  • Neptune was discovered in 1846, after analysis of Uranus’s orbit indicated its presence

  • Details of Neptune cannot be made out from Earth either

13.2 Orbital and Physical Properties

  • Uranus and Neptune are very similar

  • Uranus

    • Mass: 14,5 x Earth

    • Radius: 4.0 x Earth

    • Density: 1300 kg/m³

  • Neptune

    • Mass: 17.1 x Earth

    • Radius: 3.9 x Earth

    • Density: 1600 kg/m³

  • Peculiarity of Uranus: Axis of rotation lies almost in the plane of its orbit. Seasonal variations are extreme

13.3 The Atmosphere of Uranus and Neptune

  • Outer atmosphere of Uranus and Neptune are similar to those of Jupiter and Saturn

  • Uranus and Neptune are cold enough that ammonia freezes; methane dominates and gives the characteristic blue color

  • Clouds only in lower, warmer layers

  • Band structure of Neptune is more visible; it had a “Dark Spot” similar to Jupiter’s storms (now vanished)

13.4 Magnetospheres and Internal Structure

  • Uranus and Neptune both have substantial magnetic fields< but at a large angle to their rotation axes

13.5 The Moon System’s of Uranus and Neptune

  • Uranus has 27 moons, five of which are major: Miranda, Ariel, Umbriel, Titania, and Oberon

  • Neptune has 13 moons, but only two can be seen from Earth: Triton and Nereid

  • Further away from the Sun so they have more moons because they are the biggest in their neighborhood

13.6 The Rings of the Outermost Jovian Planets

  • Uranus and Neptune have faint ring systems, recently detected via stellar occultation

  • Uranus has narrow rings

  • Neptune has five rings: three narrow and two wide