The Solar System

532 PART 4^ |^ THE SOLAR SYSTEM

draws it out into a long tail extending away from the planet in

the direction opposite the sun. Th e rapid rotation of Uranus and

its high inclination give the magnetosphere and its long exten-

sion a corkscrew shape. At the time Voyager 2 fl ew past in 1986,

the south pole of Uranus was pointed nearly at the sun, and once

during each rotation the solar wind poured down into the south

magnetic pole. Th e resulting interaction produced strong auroras

that Voyager 2 detected in the ultraviolet at both magnetic poles

(■ Figure 24-8). In the years since, Uranus has moved farther

solar wind and traps some charged particles to create weak radiation
belts in the planet’s magnetosphere. High-speed electrons spiraling
along the magnetic fi eld produce synchrotron radio emission just as
around Jupiter, and the Voyager 2 spacecraft recorded this radiation
fl uctuating with a period of 17.2 hours—the period of rotation of
the magnetic fi eld and, presumably, the planetary interior.
Th e magnetic fi eld and the high inclination of the planet
produce some peculiar eff ects. As is the case for all planets with
magnetic fi elds, the solar wind deforms the magnetosphere and

■ Figure 24-7

The magnetic fi elds of Uranus and Neptune are peculiar. While the magnetic axis of Jupiter is tipped only 10° from its axis of

rotation, and the magnetic axis of Saturn is not tipped at all, the magnetic axes of Uranus and Neptune are tipped at large

angles. Furthermore, the magnetic fi elds of Uranus and Neptune are offset from the center of the planet. This suggests that the

dynamo effect operates differently in Uranus and Neptune than in Jupiter, Saturn, and Earth.

N

S NS NS

N

S

Magnetic N

axis N

N

N

S S

S

S

Jupiter Saturn Uranus Neptune

■ Figure 24-8

Auroras on Uranus were detected in the ultraviolet by the Voyager 2 spacecraft when it fl ew by in 1986. These maps of opposite

sides of Uranus show the location of auroras near the magnetic poles. Recall that the magnetic fi eld is highly inclined and offset

from the planet’s center, so the magnetic poles do not lie near the poles defi ned by rotation. The white dashed line marks zero

longitude. (Courtesy Floyd Herbert, LPL)

UV image

ab

UV image