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Saturn from Cassini Astronomy 161:
An Introduction to Solar System Astronomy
Prof. Richard Pogge, MTWThF 9:30

Lecture 38:
Uranus & Neptune

Uranus & Neptune

Key Ideas:

Uranus & Neptune are the outermost of the Jovian planets.



Comparison of the Jovian Planets

Orbits of Uranus & Neptune

Semi-Major Axis: a = 19.2 AU
Orbital Period: P = 84 years
Eccentricity: e = 0.05
Inclination: i = 0.8°

Semi-Major Axis: a = 30.1 AU
Orbital Period: P = 165 years
Eccentricity: e = 0.01
Inclination: i = 1.8°

Properties of Uranus & Neptune

Equatorial Radius: R = 25,559 km (4.01 REarth)
Mass: M = 14.5 MEarth
Rotation Period: 17h 14m
Axis Tilt: 97.9°!
27 moons, and thin, dark rings

Equatorial Radius: R = 24,766 km (3.88 REarth)
Mass: M = 17.1 MEarth
Rotation Period: 16h 07m
Axis Tilt: 29.6°
13 Moons and very dark, uneven rings and ring arcs.

Spacecraft studies

Voyager 2 flew by Uranus & Neptune:

Both have been extensively studied using the Hubble Space Telescope:

New studies are being enabled by the use of adaptive optics to "detwinkle" the atmosphere of the Earth and provide views of Hubble-type clarity from the ground.

Uranus & Neptune the Twins

Uranus & Neptune are near twins:

Both appear bluish/green in color:

Interiors of Uranus & Neptune

The interior structures of both are very similar:

Both lack the deep metallic hydrogen mantles found on Jupiter & Saturn because of their smaller size (pressure never gets high enough inside).

Uranus' Atmosphere

Uranus appears as a virtually featureless hazy blue ball.

Occasional clouds/storms seen in the infrared with the Hubble Space Telescope.

Neptune's Atmosphere

Neptune, like Jupiter & Saturn, radiates about 2.7x as much energy as it receives from the Sun.

Uranus' Extreme Seasons

The rotation axis of Uranus is tilted ~98°

Get extreme seasonal variations driven by uneven heating between hemispheres:

Such extreme seasonal variations may help account for Uranus' lack of weather (the strong hemispheric difference may interfere with the processes in bands and zones that are seen on the other Jovian planets).

The Moons of Uranus & Neptune

Uranus has 27 moons:

Neptune has 13 moons:

We will take a closer look at Triton along side Pluto and Charon which it closely resembles in its properties.

Comparison of the Jovian Planets

Jupiter & Saturn:

Uranus & Neptune:

Magnetic Fields

All Jovian planets have strong magnetic fields

Uranus & Neptune have off-center fields:

Nobody knows why, though a few ideas are being worked on.

Readings in Universe: Chapter 16, sections 16-1 through 16-5
Return to [ Unit 6 Index | Astronomy 161 Main Page ]
Updated: 2006 November 8
Copyright Richard W. Pogge, All Rights Reserved.