The Jovian Planets - Mesa Community College

The Jovian Planets

Exploration of the Jovian PlanetsThe outer planets have been visited by several

spacecraft, but only two have stayed in orbit:

• Pioneer 10 and 11 visited Jupiter and Saturn,• Voyager 1 and 2 visited all 4 jovian planets,• the Ulysses solar mission, flyby of Jupiter,• Galileo orbited Jupiter, 1995-2003• Cassini flyby of Jupiter, Saturn orbit since 2004,• New Horizons flyby of Jupiter, en route to Pluto

Each of these missions has provided information about the planets, their moons, and rings.

Terrestrial vs. Jovian Planets

Terrestrial vs. Jovian PlanetsDensity of terrestrial worlds (3.3 – 5.5 grams per cm3)

indicate they are made of rock and metal.

Density of jovian planets (0.7 – 1.6 grams per cm3) indicate they are made of lower density stuff.

Current models of the jovian interiors start with a small core of rock and metal at the center.

On top of that is a thick atmosphere of hydrogen and helium gas.

The thick atmospheres of the jovian planets mean they have no solid surface.

Internal StructureLower layers inside an atmosphere must support the weight of the upper layers.

Locations deeper inside an atmosphere must have larger pressures & higher temperatures to support the upper layers.

Internal StructureDue to their enormous sizes, the pressures inside Jupiter and Saturn are so high that hydrogen is squeezed into a liquid and hydrogen compounds (CH4, NH3, H2O) are squeezed into solids (“ices”).

Jupiter’s density tells us about the interior.

Laboratory studies of H & He tell us how gases behave under high pressure.

Computer models predict pressure & temperature.

Jupiter’s Internal Structure

Uranus & Neptune are essentially twins. They have nearly the same mass and composition.

They both formed far from the Sun where ices were very common, so their cores are rich in ices.

They probably grew slowly since collisions would be slower and less frequent that far from the Sun.

It is thought that they didn’t gather as much gas as Jupiter and Saturn.

So they are mostly core with “thin” atmospheres.

Uranus & Neptune

Uranus & Neptune are more ice and rock than gas. Astronomers call them “ice giants” to divide them from Jupiter & Saturn, which are mostly H & He.

The Ice Giants: Uranus & Neptune

Which of the jovian planets have solid surfaces?

A. Jupiter & Saturn

B. Uranus & Neptune

C. All four planets

D. None of them

Magnetic FieldsThe recipe for a magnetic field, dynamo theory:

1. Fast rotation

2. Interior filled with electrically conducting fluid

3. Hot interior that undergoes convection

Observations:

1. All 4 jovian planets rotate in less than 20 hours

2. Jupiter & Saturn contain metallic hydrogen

3. All 4 jovian planets have hot interiors

Magnetic Fields

Jupiter: strongest magnetic field of any planet, 20000x Earth

Saturn: 600x Earth, less metallic H, less magnetic field

Uranus & Neptune: no metallic hydrogen, but both have fields about 50x Earth’s

MagnetospheresThe fields of Earth, Jupiter, and Saturn are aligned with their rotation axes and centered in the cores.

The fields of Uranus & Neptune are neither aligned nor centered in the core: generated by oceans?

Auroras on Jupiter & Saturn

The atmosphere has very high speed windsand hurricane-like activity, shown here in a movie recorded by Voyager 1 in 1979.

One frame was taken each time the Great Red Spot was visible.

The Atmosphere of Jupiter

The largest circular feature in Jupiter’s atmosphere is the Great Red Spot.

First observed in 1643.

This single storm could easily hold several Earths.

The Atmosphere of Jupiter

Storms A’Plenty

There are no storms in Earth’s atmosphere that last for several centuries.

An ongoing topic of Jupiter research is how the planet’s storms keep going for so long.

This Cassini movie shows Jupiter unrolled.

Saturn’s AtmosphereStorms are visible on Saturn, but they are far less colorful and much shorter lived.

New infrared observations of storms at Saturn’s poles is reviving interest in Saturn’s atmosphere.

The Atmosphere of Uranus

Hubble Space Telescope

images (1999)

Uranus’ unusual heating from the Sun may play a role in its “blank” atmosphere. Seasonal changes may produce formation of clouds or storms.

Voyager 2 flyby images (1986) showed no clouds or storms.

(Left) natural color,

(Right) enhanced color showing haze over pole.

The Atmosphere of NeptuneDuring its 1989 flyby, Voyager 2 found a Great Dark Spot that appeared to be similar to Jupiter’s Great Red Spot. By the late 1990’s, the spot was gone.

Faster Rotation, Complex WindsThe jovian planets rotate faster than Earth so it is not surprising that the wind patterns are complex.

Winds in the zones and belts blow in opposite directions, at 100-1000 kilometers per hour!

Atmospheres: Jupiter vs. SaturnSaturn’s atmosphere is cooler and under lower pressure, so thicker, deeper cloud layers.

Jupiter’s clouds are thin, so we can see several layers.

Terrestrial planets and jovian planets do share some features. Which of the following Earthly feature is not present in/on the jovian planets?

A. rotating cyclonic storms like hurricanes

B. cores of high temperature metal

C. volcanoes, plate tectonics, and impact craters

D. magnetic fields that extend into space