The Jovian PlanetsSaturn

• Small “Core”/Atmosphere Ratio• Rings• Lots of Satellites

Jupiter

Uranus Neptune

Spacecraft Missions to the Jovian PlanetsThree Major Missions• Pioneers 10 & 11 (launched 1972)• Voyagers 1 & 2 (launched 1977)• Galileo (launched 1989)

Difficulties with sending probes to Jovian planets• Energy source: solar panels + internal radioactive

generators needed• Distance from Earth: autonomous• Destruction of spacecraft by debris: asteroids, rocks, etc.• Trajectory: gravity assisted

Flight Paths of Voyager Spacecraft

• Gravity-assisted Trajectories

Trajectory video – Cassini Spacecraft (arrival date to Saturn –2004)

Where are the Voyager Spacecraft?

Deep Space Network – Antenna locations

• Voyager 1 & 2 continue to transmit signals back to Earth• They are continuously monitored by the Deep Space

Network

• Present mission – Find the edge of the Solar System (Video)

The Jovian Planets• How do we determine the nature of their interiors?→ Mass, radius, rotation rate, heat balance, atmospheric

composition, gravitational effects on moons• Composition→ Primarily Hydrogen & Helium, plus methane, ammonia,

water ice, etc…→ Dense core: required to account for gravitational field;

composed of things denser than Hydrogen & Helium (Silicon, metals, heavy volatiles?)

• Note: The behavior of Hydrogen & Helium at high temperatures & pressures is not well understood

Sizes of Jovian planets compared to the Earth

14 Mearth317 Mearth 90 Mearth 17 Mearth

Properties of Jupiter• Composition: 75%

hydrogen, 24% helium + methane, ammonia, water ice…

• Average Distance from the Sun: 0.7 light hours

• Rotation Rate

• Orbital Period: 11.9 Earth years

• Axis Tilt: 3.1°• Number of Moons: ~ 61

9h55m30s – Magnetic Field9h50m30s – Equatorial Clouds9h55m41s – High Latitude CloudsNote: Hydrogen and Helium

are colorless.

Moons are being found at a regular rate around the Jovian planets

Technique is similar toKuiper Belt search

The moon Io and Jupiter

Properties of Saturn• Average Distance from

the Sun: 1.3 light hours• Rotation Rate

• Orbital Period: 29.5 Earth years

• Axis Tilt: 27° (i.e., Seasons: UV + Methane → Ethane in the Summer

• Number of Moons: ~ 31• Equator is 10% wider than

pole-to-pole

10h39m24s – Magnetic Field10h14m – Equatorial Clouds10h40m – High Latitude Clouds

Note: tan “smog” that overliesclouds below gives Saturn itscolor.

The Jovian planets have equatorial bulges

• Rotation Rates ~ 10-17 hours• Gravity makes planets spherical• Rotation makes planets bulge at the equator(Note: This keeps rings/satellites aligned with equator)

Jupiter & Saturn are about as large as planets can be

Internal Heat SourcesJupiter & Saturn radiate twice as much heat as they receive

from the Sun• Earth radiates 0.005% as much energy as it receives

from the Sun

Source of heat from Jupiter is the slow contraction of the planet

• Gravitational potential energy → kinetic energy →thermal energy

Source of heat from Saturn is Helium rain• At lower temperature & pressure of Saturn, liquid helium

does not dissolve with liquid hydrogen• Deficit of Helium relative to Hydrogen has been

measured in the outer atmosphere of Saturn

Probing Jupiter’s Atmosphere – The Galileo Probe (video)

1995: Galileo probe dropped into Jupiter’s atmosphere

cold enough for water tocondense, etc…

Troposphere: turbulent clouds due to the Greenhouse effect

(UV)

JovianAtmosphere Comparison

Internal structure of Jupiter

Belts & Zones• Strong Coriolis forces

divide circulation cells into bands

• Convection results in bands of different color

→ Zones: rising, cooling air out of which ammonia condenses into clouds

→ Belts: falling air depleted in clouds; allows clouds below to be seen

The Great Red Spot

• Storm that has persisted for at least 300 years

• Size: twice as wide as the Earth

• Why are such storms so long-lived?

→ No solid surface to sap away energy (as happens on the Earth)

Magnetic Fields

Auroras of Jupiter

Flux tube connecting satellites to Jupiter

Ultraviolet

Rings• Composition: mixture of

rocks of varying sizes comprised mostly of water ice (high albedo)

• Dimensions of Saturn’s rings: 270,000 km x 10s of meters

• Roche zone: tidal forces ~ binding gravitational forces

• Note: smaller rocks are held together by gravitational & electrostatic forces, & thus can survive

Jupiter’s Rings• Jupiter’s rings are less

prominent than Saturn’s• Why? Smaller particles

Features in Rings• Gaps are present in the

rings. They are created by Gap Moons that nudge particles out of particular orbits

• Spokes: particles levitated out of ring plane by forces associated with the magnetic fields

Origin of Rings• Moon that strayed too

close• Tidal forces prevented a

Moon from ever forming there

Formation of Jovian Planets & Satellites

• Ice & Rock cores build→ Mass ~ 10 Earth Masses

• Hydrogen & Helium from surrounding solar nebulae were gravitationally captured

→ Planets that are massive & cold enough can retain hydrogen & helium

• Solid grains in surrounding nebula form satellites