The Gas Giants: Jupiter and Saturn

The Gas Giants: Outer Atmosphere

Zonal flows (observed as bands)

Composition of Jupiter's outer layers in the atmosphere is mostly hydrogen and helium, similar to the Sun

Saturn has a deficit of helium in its outer atmosphere

Differential rotation:

Example Jupiter: Equatorial regions rotate faster (9h 50m) than polar regions (9h 55m)

Weather

Small scale weather patterns

Great red spot on Jupiter

Storms are thought to be supported by large scale atmospheric motion

Colors are determined by:

chemistry (perhaps sulfur compounds produce different shades)

depth of the layer that is visible - brown oval

Storms

Saturn (Fig 12.5) false color image highlights storms

Jupiter (Fig 11.8) Great red spot and white oval (high cloud tops)

Zones and Belts

Different latitudes are divided into zones and belts (areas of rising and falling atmosphere due to convection). (Fig 11.4 and 11.5)

Galileo probe of Jupiter's Atmosphere

Winds are present at large depths

Implies heat source is from planet not solar heating

No complex organic molecules found, no evidence of prebiotic compounds or bacteria

Ethane ( C₂ H₆) was found, simple carbon-based molecule

Phosphine (PH₃ ) found, may be a coloring agent

Atmosphere

Atmosphere

Equatorial Bulge

Equatorial bulge is the result of gravity and rotation (Fig. 11.2)

Interiors

Both Jupiter and Saturn have large rocky cores, based on measurements of equatorial bulge

Layer of metallic hydrogen

Internal Heat Source

Both Jupiter and Saturn have internal heat sources (give off more energy than they receive from the Sun)

Jupiter's heat source is the heat from planet formation and gravitational collapse

Saturn's heat source is from liquid helium precipitation. This process removes helium and explains helium deficit in outer layers.

Magnetosphere

Fig 11.11, 11.13, 11.12, 12.9

Planet Rings

False color image of Saturn's rings 12.13, rings are very complex

Jupiter's small ring discovered by both Voyager spacecraft 11.25

Saturn Up Close

Rings are probably short-lived

Need constant replenishing

Fig 12.10

Fig 12.10

Ring Orientation

Ring brightness depends on orientation, Fig 12.1

Ring Composition

Rotational and thermal studies showed the rings must be composed of particles (not solid, liquid, or gas)

80% reflectivity (albedo) suggests icy composition

Water ice in rings has been confirmed by satellites

Most particles are similar in size and composition as a large snowball

Rings are truly thin- 10 m thick in places

Due to collisions between ring particles, asymmetric gravitational field of Saturn due to its equatorial bulge keeps rings in Saturn's equatorial plane

Ring Dynamics

Shepherd moons (Fig. 12.16, 12.17, 12.18)

Roche Limit

Tidal force stretches out planets along the direction to the planet

Roche limit= tidal stability limit

Inside this limit, a planet is destroyed by tidal forces

Galilean Satellites

Moon system of Jupiter is like a mini-solar system

Moon density decreases with distance from Jupiter

Io

Volcanically active

Heat source is caused by tidal stresses on satellite

Europa and Ganymede

Water below icy surfaces?

Dark regions caused by meteoritic dust- oldest regions

Plate tectonics or subsurface water action?

Saturn's Largest Satellite Titan

Atmosphere (90% N), dense

Rocky core, surrounded by water ice (based on density)?

Saturn's Medium Sized Satellites

Circular orbits

Tidally locked

No correlation of density with distance from Saturn

Small Satellites: Complicated Orbits

Janus and Epimetheus: orbit sharing satellites

Synchronous orbits about Tethys