Geology Reference
In-Depth Information
Figure 10.2. Neptune
is Great Dark Spot is shown in this Voyager 2
image, along with several other features in the upper atmosphere
(NASA Voyager 2 PIA02219).
'
Figure 10.1. Uranus was the
first planet to be discovered in historic
times. As shown in this Hubble Space Telescope image, Uranus lies
“
with the spin axis inclined about 82° to the ecliptic
plane. Haze, cloud patterns, and the tracks of faint rings and small
satellites form a bull
on its side
”
s eye pattern around the south pole of the
planet. Eight of Uranus
'
Voyager images indicated wind speeds up to 580 m/s in
Neptune
'
small moons are shown here (NASA Hubble
s atmosphere.
Earth-based and spacecraft data show that all of the
giant planets possess ring systems. Uranus
'
rings,
rst
discovered from telescopic observations in 1977, are
now seen to include at least 13 sets, some of which are
broad and diffuse, others of which are narrow and have
sharp boundaries. Particles in the rings range in size from
microns to meters in diameter and are very dark, similar to
soot. Uranus
'
rings could represent one or more moons
that were smashed apart by collisions. Neptune has at least
six ring systems, all of which are very faint and are named
after individuals who contributed to Neptune science in
the 1800s. The outermost main ring, named Adams Ring,
consists of
five arc-segments, which are thought to be held
in place by Galetea, a small moon.
'
PIA01278).
de
nitive answer has been offered to explain this orienta-
tion, it is commonly thought that an enormous impact
might have knocked Uranus on its side. At visible wave-
lengths, both Uranus and Neptune appear rather bland,
with only hints of any structure in the upper atmosphere.
Uranus is the coldest major planet in the Solar System,
generating far less heat from the interior than Neptune. In
natural color, Uranus
south polar region appears
brownish-orange, while Neptune has an overall bluish
cast. In the infrared, however, features such as small
clouds, bands, and other structures are revealed. For
example, Hubble Space Telescope views of both planets
show more detail of these features than indicated in
Voyager images. While atmospheric features of both plan-
ets are much more subdued than those of Jupiter and
Saturn, Neptune shows much more activity than Uranus,
perhaps driven by the greater amount of heat released
from its deep interior. For example, Voyager images
show a feature resembling Jupiter
'
s Great Red Spot, lead-
ing to its name, the Great Dark Spot (
Fig. 10.2
), which
probably is driven by thermal up-welling in the atmos-
phere. Tracking of other cloud features in sequential
'
10.3 Uranian moons
Uranus has at least 27 moons, but those of geologic
interest are (from Uranus outward) Miranda, Ariel,
Umbria, Titania, and Oberon (
Fig. 10.3
), named after
characters from Shakespeare
'
s AMidsummerNight
'
s
Dream and The Tempest and Pope
'
s The Rape of the
Lock. All of the moons are in synchronous rotation,
and their densities of 1.5 to 1.7 g/cm
3
are higher than
