skip navigation
Saturn from Cassini Astronomy 161:
An Introduction to Solar System Astronomy
Prof. Richard Pogge, MTWThF 2:30

Lecture 37: The Gas Giants:
Jupiter & Saturn

Jupiter from Cassini Saturn from Cassini
Images from the Cassini Spacecraft [NASA/JPL]

Key Ideas:

Jupiter & Saturn are the largest Planets

Cloud Features:

Atmosphere & Internal Structure:

Jupiter at a Glance

Orbital Data
Semi-Major Axis: a = 5.2 AU
Orbital Period: P = 11.9 years
Eccentricity: e = 0.048
Inclination: i = 1.3°

Planetary Data
Equatorial Radius: R = 71,492 km (11.21 REarth)
Mass: M = 317.7 MEarth
Rotation Period: 9h 50m
Axis Tilt: 3.1°
63 Moons & a faint ring system

Spacecraft to Jupiter



Saturn at a Glance

Orbital Data:
Semi-Major Axis: a = 9.5 AU
Orbital Period: P = 29.5 years
Eccentricity: e = 0.056
Inclination: i = 2.5°

Planetary Data:
Equatorial Radius: R = 60,268 km (9.44 REarth)
Mass: M = 95.2 MEarth
Rotation Period: 10h 14m
Axis Tilt: 26.7°
60 Moons & a spectacular ring system

Spacecraft Visits to Saturn



Jupiter & Saturn are Gas Giants

Have no solid surface:

Rotate rapidly as measured from their magnetic fields:

This rapid rotation noticably flattens the planets at the poles:

Atmospheres of Jupiter & Saturn

Composition The main constituents of the atmospheres of Jupiter and Saturn are:
 Jupiter Saturn
Hydrogen (H2) 86% >93%
Helium (He) 14% >5%
Methane (CH4) 0.1% 0.2%
Water Vapor (H2O) 0.1% 0.1%
Ammonia (NH3) 0.02% 0.01%

These are examples of Reducing Atmospheres, which are atmospheres dominated by Hydrogen Chemistry (CH4, H2O, NH3).

By comparison, Terrestrial planets Oxidizing Atmospheres, dominated by Oxygen chemistry (CO2, H2O, N2).

The Clouds of Jupiter

What we see as the "surface" of Jupiter are the tops of the clouds:

The atmosphere of Jupiter is divided into East-West latitudinal bands:

There are also Cyclonic storms that appear in the regions between Belts and Zones.

Belts & Zones

Belts: high pressure, high temperature

Zones: low pressure, low temperature

Cyclonic Storms

Get strong winds at the belt/zone boundaries:

Results in strong cyclonic storms:

The Great Red Spot

Largest and most complex of Jupiter's storms:

The Atmosphere of Saturn

The atmosphere of Saturn is also divided into dark bands & bright zones like Jupiter's atmosphere, but...

Internal Energy

Jupiter and Saturn radiate more energy at Infrared wavelengths than they receive from the Sun.

Energy Source:

This internal heat helps power the weather seen on Jupiter and Saturn.

By contrast, the weather on the Earth, Venus, and Mars is powered by solar energy (internal "geothermal" heat is insignificant compared to sunlight).

Interior of the Gas Giants

Atmosphere gets thicker the deeper you go, and the pressure rises dramatically:

At the bottom is a massive rock & ice core of 10-15 MEarth & ~1.5 REarth.

Magnetic Fields

Circulating currents in the electrically conductive metallic hydrogen "mantles" of Jupiter & Saturn generates powerful magnetic fields: Magnetic field co-rotates with the interior of the planet Rotating magnetic field also generates radio-wavelength emission

Saturn vs. Jupiter

Saturn is different from Jupiter in a number of important ways:
Return to [ Unit 6 Index | Astronomy 161 Main Page ]
Updated: 2007 November 10
Copyright Richard W. Pogge, All Rights Reserved.