The date of each photograph and the distance of the spacecraft from
the planet or satellite are included with each picture.
[Illustration: 2/5/79 28.4 million km (17.6 million mi)
Jupiter is the largest planet in our solar system, with a diameter
11 times that of Earth. Jupiter rotates very quickly, making one
full rotation in just under ten hours. Composed primarily of
hydrogen and helium, Jupiter’s colorfully banded atmosphere displays
complex patterns highlighted by the Great Red Spot, a large,
circulating atmospheric disturbance. Three of Jupiter’s 13 known
satellites are also visible in this Voyager 1 photograph. The
innermost large satellite, Io, can be seen in front of Jupiter and
is distinguished by its bright, orange surface. To the right of
Jupiter is Europa, also very bright but with fainter surface
markings. Callisto is barely visible beneath Jupiter. These
satellites orbit Jupiter in the equatorial plane and appear in their
present position because Voyager is above the plane.]
[Illustration: Jupiter’s atmosphere is undergoing constant change,
presenting an ever-shifting face to observers. The Great Red Spot
has undergone three major periods of activity in the last 15 years.
These images of Jupiter, taken by Voyager 1 (top) and Voyager 2
(bottom) almost four months apart, show that cloud movement in the
Jovian atmosphere is not uniform because wind speeds vary at
different latitudes. For example, the white ovals which appear below
the Great Red Spot dramatically shifted between January and May, the
time interval between these two pictures. The bright “tongue”
extending upward from the Great Red Spot interacted with a thin,
bright cloud above it that had traveled twice around Jupiter in four
months. Eddy patterns to the left of the Great Red Spot, which have
been observed since 1975, appear to be breaking up.]
[Illustration: 1/24/79 40 million km (25 million mi)]
[Illustration: 5/9/79 46.3 million km (28.7 million mi)]
[Illustration: 2/25/79 9.2 million km (5.7 million mi)
The Great Red Spot on Jupiter is a tremendous atmospheric storm,
twice the size of Earth, that has been observed for centuries. The
Great Red Spot rotates counterclockwise with one revolution every
six days. Wind currents on the top flow east to west, and currents
on the bottom flow west to east. This Voyager 1 picture shows the
complex flow and turbulent patterns that result from the Great Red
Spot’s interactions with these flows. The large white oval is a
similar, but smaller, storm center that has existed for about 40
years.]
[Illustration: 7/3/79 6 million km (3.72 million mi)
A comparison of the Voyager 2 photograph above with the preceding
Voyager 1 photograph shows several distinct changes in the Jovian
atmosphere around the Great Red Spot. The white oval beneath the
Great Red Spot in the first picture has moved farther around
Jupiter, and a different white oval has appeared under the Great Red
Spot in the Voyager 2 picture taken four months later. The disturbed
cloud regions around the Great Red Spot have noticeably changed, and
the white zone west of the Great Red Spot has narrowed.]
[Illustration: 3/2/79 4 million km (2.5 million mi)
High-speed wind currents in the mid-latitudes of Jupiter are shown
in this high-resolution Voyager 1 photograph. The pale orange line
running diagonally to the upper right is the high-speed north
temperate current with a wind speed of about 120 meters per second
(260 miles per hour), over twice as fast as severe hurricane winds
on Earth. Toward the top of the picture, a weaker jet of
approximately 30 meters per second (65 miles per hour) is
characterized by wave patterns and cloud features that rotate in a
clockwise manner.]
[Illustration: 3/2/79 4 million km (2.5 million mi)
The large brown-colored oval appearing in this Voyager 1 picture was
selected as one of the targets to be photographed near closest
approach to Jupiter because it is probably an opening in the upper
cloud deck that exposes deeper, warmer cloud levels. Brown ovals
(which can also be seen in the preceding and following photographs)
are common features in Jupiter’s northern latitudes and have an
average lifetime of one to two years.]
[Illustration: 6/28/79 10.3 million km (6.4 million mi)
Jupiter’s Equatorial Zone is the broad, orange band that traverses
the center of this Voyager 2 picture. This zone is characterized by
the wispy clouds along its northern edge. The brown oval was
observed by Voyager 1 four months earlier, illustrating the
stability of this type of feature in the Jovian atmosphere. In
contrast, the turbulent region in the lower right of the picture,
which lies just to the left of the Great Red Spot, shows features
that are relatively short lived. With the exception of the cooler
Great Red Spot, as colors range from white to orange to brown, we
are generally looking at deeper and warmer layers in the Jovian
atmosphere.]
[Illustration: This infrared image of Jupiter was taken from Earth
and shows heat radiating from deep holes in Jupiter’s clouds. Bright
areas in the image are higher temperature regions than the dark
areas and correspond to parts of the atmosphere that are relatively
free of obscuring clouds. The Great Red Spot appears on the left
limb, or edge of the planet, as a dark area encircled by a bright
ring, indicating that the Spot is cooler than the surrounding
region. The infrared image was recorded by the 200-inch Hale
telescope on Mount Palomar in California.]
[Illustration: 1/10/79 535,000 km (332 million mi)
This Voyager 1 picture was also taken the same day, about one hour
after the infrared image.]
[Illustration: 3/5/79 515,000 km (320,000 mi)
The largest aurora ever observed, nearly 29,000 kilometers (18,000
miles) long, appears in this Voyager 1 photograph, taken on the dark
side of Jupiter six hours after closest encounter. The auroral
lights are brighter than any northern lights seen on Earth.
Jupiter’s north pole is approximately midway along the auroral arc.
This timed exposure of the aurora also shows what appear to be
lightning storms several thousand kilometers below the aurora. The
strength of the lightning bolts is comparable to that of superbolts
seen near cloud tops above Earth. Lightning had been suspected to
exist on Jupiter, but at lower levels in the atmosphere.]
[Illustration: 3/4/79 1.2 million km (750,000 mi)
The first evidence of a ring around Jupiter is seen in this
photograph taken by Voyager 1. This photograph was part of a
sequence planned to search for such rings around Jupiter. The
multiple image of the extremely thin, faint ring appears as a broad
light band crossing the center of the picture. This multiple image
and the elongated, wavy motion of the background stars are due to
the 11-minute, 12-second exposure and the very slow natural
oscillation of the spacecraft. The ring, which is in Jupiter’s
equatorial plane, is invisible from Earth because of its thinness
and transparency and because of Jupiter’s brightness. The black dots
in the picture are calibration points in the camera.]
[Illustration: Because of Voyager 1’s discovery of a ring around
Jupiter, Voyager 2 was programmed to take additional pictures of the
ring. These three Voyager 2 images show Jupiter’s ring in
progressively higher resolution. The pictures were taken when
Jupiter was eclipsed by the Sun, and the ring appears unusually
bright because of the forward scattering of sunlight by small ring
particles.]
[Illustration: 7/10/79 1.45 million km (900,000 mi)
In this four-picture mosaic, the arms of the ring curving toward the
spacecraft (on the near side of the planet) are cut off by the
planet’s shadow. Scientists estimate that the distance from the
Jovian cloud tops to the outer edge of the ring is 55,000 kilometers
(35,000 miles).]
[Illustration: 7/10/79 1.55 million km (961,000 mi)
In this picture, which is composed of six images, there is evidence
of structure within the ring, but the spacecraft motion during these
long exposures obscured the highest resolution detail. However,
there is speculation that the ring width, estimated at 6000
kilometers (4000 miles), contains more than one ring.]
[Illustration: 7/10/79 1.45 million km (900,000 mi)
This photograph is an enlargement of the isolated left frame in the
first picture and reveals a density gradient of very small particles
extending inward from the ring. The thickness of the ring has been
estimated at less than one kilometer (0.6 mile) although the ring
appears about 30 kilometers (19 miles) thick in the image, due to
camera motion and finite resolution. Composition of the low-albedo
(dark) particles is not known, but particle size probably ranges
from microscopic to at most a few meters in diameter. If collected
together to form a single body, the total mass of the Jovian rings
would form an object with a diameter less than twice that of tiny
Amalthea.]
[Illustration: 2/13/79 20 million km (12.4 million mi)
Jupiter and two of its planet-sized satellites, Io at left and
Europa at right, are visible in this Voyager 1 picture. Jupiter’s
four largest satellites—Io, Europa, Ganymede and Callisto—were
discovered in 1610 by Galileo Galilei. The two outer Galilean
satellites are Ganymede and Callisto, not shown in this picture. All
four satellites probably formed about four billion years ago but
their surfaces vary in age tremendously. Io and Europa have younger,
more active surfaces than Ganymede and Callisto. Like our Moon, the
satellites keep the same face toward Jupiter. In this picture, the
sides of the satellites that always face away from the planet are
visible.]
[Illustration: Amalthea, Jupiter’s innermost satellite, was
discovered in 1892. It is so small and close to Jupiter that it is
extremely difficult to observe from Earth. Amalthea’s surface is
dark and red, quite unlike any of the Galilean satellites. The three
Voyager 1 pictures and the one Voyager 2 picture following (seen
against the disk of Jupiter) reveal a small, elongated object, about
265 kilometers (165 miles) long and 150 kilometers (90 miles) in
diameter. Amalthea keeps its long axis pointed toward Jupiter as it
orbits around the planet every 12 hours.]
[Illustration: 3/4/79 1.25 million km (780,000 mi)]
[Illustration: 3/4/79 695,000 km (430,000 mi)]
[Illustration: 3/5/79 425,000 km (264,000 mi)]
[Illustration: 7/9/79 560,000 km (350,000 mi)
Amalthea was observed end-on in the Voyager 2 picture, which has
been computer-processed to enhance the image.]
[Illustration: 3/4/79 377,000 km (234,000 mi)
Io, Jupiter’s innermost Galilean satellite, displays great diversity
in color and brightness. This Voyager 1 four-picture mosaic shows
Io’s complex coloration of red-orange, black, and white regions, and
the two major topographic features: volcanic regions, the most
prominent of which is the “hoofprint” (volcanic deposition feature)
in the center-right, and the intervolcanic plains that are
relatively featureless. Io’s vivid coloring is probably due to its
composition of sulfur-rich materials that have been brought to the
surface by volcanic activity.]
[Illustration: 3/5/79 129,600 km (80,500 mi)
The bright area at the upper right in this Voyager 1 picture of Io
appears to be a caldera (collapsed volcano) that is venting clouds
of gases. The clouds may condense to form extremely fine particles
that scatter light and appear blue. Because the infrared
spectrometer discovered sulfur dioxide on Io, scientists believe
this gas may be the main component of the clouds. Sulfur dioxide
clouds would rapidly freeze and snow back to the surface. It is also
possible that dark areas in the floors of the calderas are pools of
encrusted liquid sulfur.]
[Illustration: 3/5/79 66,000 km (41,000 mi)
Evidence of erosion in Io’s southern polar region is visible in this
Voyager 1 high-resolution image. The picture has been
computer-enhanced to bring out surface detail while suppressing
bright markings. A depressed segment of the crust, bounded by
faults, is seen near the terminator in the upper right portion of
the image. At the lower center are complicated scarps (slopes) and
portions of isolated elevated terrain that geologists interpret as
“islands” left behind as the scarps eroded. Scientists speculate
that sulfur dioxide (as a subsurface liquid) may be a determinant in
the creation of these features.]
[Illustration: 3/4/79 862,000 km (540,000 mi)
Io’s surface, less than ten million years old, is quite young
compared to the other Galilean satellites and to other terrestrial
bodies, such as Mercury and the Moon. The surface is composed of
large amounts of sulfur and sulfur dioxide frost, both of which
account for most of the surface color. This picture was taken by
Voyager 1. Material deposited by the volcano (see following
pictures) can be seen as a white ring near the center of Io.]
[Illustration: The first active volcanic eruptions other than on
Earth were discovered on Io. These volcanoes are extremely explosive
with ejection velocities of more than one kilometer per second (2200
miles per hour), which is more violent than Etna, Vesuvius, or
Krakatoa on Earth. Both pictures below were taken by Voyager 1.]
[Illustration: 3/4/79 450,000 km (280,000 mi)
In this picture, the plume visible on the right edge extends more
than 100 kilometers (60 miles) above the surface.]
[Illustration: 3/4/79 499,000 km (310,000 mi)
The same volcano is shown in this picture, photographed one hour and
52 minutes earlier.]
[Illustration: 3/4/79 490,000 km (304,000 mi)
Special color reconstruction by means of ultraviolet, blue, green,
and orange filters allowed scientists to study the amount of gas and
dust and the size of the dust particles that erupted from the
volcano on Io shown in this Voyager 1 image. The region that is
brighter in the ultraviolet (blue area) is about 210 kilometers (130
miles) high, over twice the height of the denser, bright yellow
core. The vent area is visible on page 18 as a dark ring in the
upper left region of Io.]
[Illustration: 7/10/79 1.2 million km (750,000 mi)
Of the eight active volcanoes discovered on Io by Voyager 1, six of
the seven volcanoes sighted by Voyager 2 were still active. The
giant volcano observed by Voyager 1 over the “hoofprint” region (see
page 18) had become inactive. Scientists, therefore, believe that
the satellite is undergoing continuous volcanic activity, making
Io’s surface the most active in the solar system. This Voyager 2
photograph, which shows three active volcanoes, was one of the last
of an extensive sequence of “volcano watch” pictures planned as a
result of Voyager 1’s volcano discovery. The black dots are
calibration points on the camera.]
[Illustration: 7/8/79 1.2 million km (750,000 mi)
Europa, approximately the same size and density as our Moon, is the
brightest Galilean satellite. The surface displays a complex array
of streaks, indicating that the crust has been fractured. In
contrast to its icy neighbors Ganymede and Callisto, Europa has very
few impact craters. The relative absence of features and low
topography indicate that the crust is young and probably warm a few
kilometers below the surface. The warmth is probably due to a
combination of radioactive and tidal heating. The tidal heating
within Europa is estimated to be ten percent that of the stronger
tidal heating effect within Io. The regions that appear blue in this
Voyager 2 image are actually white.]
[Illustration: 7/9/79 240,000 km (150,000 mi)
Europa’s surface is probably a thin ice crust overlying water or
softer ice (slush) about 100 kilometers (60 miles) thick that covers
a silicate interior. The tectonic processes on Europa’s surface
create patterns that are drastically different from the fault
systems seen on Ganymede’s surface, where pieces of the crust have
moved relative to each other. On Europa, the crust evidently
fractures, but the pieces remain roughly in their original position.
This Voyager 2 picture is composed of three images.]
[Illustration: 7/9/79 240,000 km (150,000 mi)
Long linear fractures or faults which crisscross Europa’s surface in
various directions are over 1000 kilometers (600 miles) long in some
places. Large fractures are 200 to 300 kilometers (125 to 185 miles)
wide, wider than the crust is thick. Also visible are somewhat
darker mottled regions that appear to have a slightly pitted
appearance. No large craters (more than five kilometers in diameter)
are identifiable in this Voyager 2 picture, indicating that this
satellite has a very young surface relative to Ganymede and
Callisto, although perhaps not as young as Io’s surface. Scientists
believe that the surface is a thin ice crust overlying water or
softer ice and that the fracture systems are breaks in the crust.
Resurfacing processes, such as the production of fresh ice or snow
along the cracks and cold glacier-like flows, have probably removed
evidence of impact events (cratering). Europa, therefore, appears to
have many properties similar to Ganymede and Io.]
[Illustration: 7/9/79 240,000 km (150,000 mi)
Complex narrow ridges, seen as curved bright streaks 5 to 10
kilometers (3 to 6 miles) wide and typically 100 kilometers (60
miles) long, characterize the surface topography of this view of
Europa. The dark bands also visible in this Voyager 2 photo are 20
to 40 kilometers (12 to 25 miles) wide and up to thousands of
kilometers long. The fractures on the icy surface are filled with
material from beneath, probably as a result of internal tidal
flexing which continually heats the thin outer ice crust. A few
features are suggestive of degraded impact craters.]
[Illustration: 3/4/79 2.6 million km (1.6 million mi)
Ganymede, Jupiter’s largest satellite, is about one and one-half
times the size of our Moon but only about half as dense and is
composed of about 50 percent water or ice and the rest rock. The
bright surface of Ganymede is a complex montage of ancient,
relatively dark and cratered terrain, grooved terrain that resulted
from a dramatic history of tectonic movement in the icy crust, and
bright young ray craters that expose fresh ice. This photograph was
taken by Voyager 1.]
[Illustration: 7/7/79 1.2 million km (750,000 mi)
The dark, cratered, circular feature in this Voyager 2 photograph is
about 3200 kilometers (2000 miles) in diameter and is on the side of
Ganymede opposite to that shown in the previous picture. This region
is apparently the largest piece of ancient, heavily cratered crust
left on Ganymede. The light branching bands are ridged and grooved
terrain which are younger than the more heavily cratered dark
regions. Despite the dramatic surface appearance, Ganymede is
relatively devoid of topographic relief due to the consequences of
glacier-like “creep” in the icy crust.]
[Illustration: 7/8/79 312,000 km (194,000 mi)
Several different types of terrain common to Ganymede’s surface are
visible in this Voyager 2 picture. The boundary of the largest
region of dark ancient terrain (also shown in the previous photo)
can be seen to the right, revealing the light linear features that
may be the remains of shock rings from an ancient impact. The broad
light regions are the typical grooved structures contained within
the light regions on Ganymede. On the lower left is another example
of what might be evidence of large-scale lateral faulting in the
crust; the band appears to be offset by a linear feature
perpendicular to it. These are the first clear examples of lateral
faulting seen on any planet other than Earth.]
[Illustration: 7/8/79 313,000 km (194,500 mi)
This color reconstruction of part of Ganymede’s northern hemisphere,
taken by Voyager 2, encompasses an area about 1300 kilometers (800
miles) across. It shows part of a dark, densely cratered region that
contains numerous craters, many with central peaks. The large bright
circular features have little relief and are probably the remnants
of old, large craters that have been annealed by the flow of icy
material near the surface. The gradually curving lines that press
through the dark region suggest the presence of a large impact basin
to the southwest, which has been obliterated by the subsequent
formation of younger grooved terrain.]
[Illustration: 3/5/79 165,000 km (103,000 mi)
A broad, north-south strip of grooved terrain on Ganymede, offset by
a traversing fault in the upper part of the picture, is shown in
this Voyager 1 photograph. There are several other perpendicular
fault lines farther down on the fault. Within the major light
stripes, the more closely spaced, shallow grooves run parallel to
the boundaries of the stripes. The larger striped features divide
the cratered terrain into isolated polygons several hundred to about
1000 kilometers (600 miles) across.]
[Illustration: 3/5/79 145,000 km (90,000 mi)
The grooved terrain at higher resolution emphasizes numerous
interwoven linear features in this Voyager 1 picture, near the
terminator on Ganymede. This suggests an early period in Ganymede’s
history when the crust was active and mobile, resembling Earth’s
plate tectonics in some ways. The causes of the extreme differences
in crustal evolution between Callisto and Ganymede are under
investigation. Combinations of radioactive heating and a greater
degree of tidal heating for Ganymede are possibilities.]
[Illustration: 7/9/79 100,000 km (62,000 ml)
This mosaic of Ganymede, composed of photographs taken by Voyager 2,
shows numerous impact craters, many with bright ray systems. The
rough terrain at the lower right is the outer portion of a large,
fresh impact basin that postdates most of the other terrain. The
dark patches of heavily cratered terrain (right center) are probably
ancient mixtures of ice and rock formed prior to the grooved
terrain. The large rayed crater at the upper center is about 150
kilometers (95 miles) in diameter.]
[Illustration: 7/8/79 85,000 km (53,000 mi)
Curved troughs and ridges in this high-resolution Voyager 2
photograph of Ganymede are the distinctive characteristics of an
enormous, ancient impact basin. The basin itself has been eroded by
later geologic processes; only the shock ring features are preserved
on the ancient surface. Near the bottom of the picture these curved
markings are perforated with the younger, grooved terrain.]
[Illustration: 7/7/79 2.3 million km (1.4 million mi)
Callisto, only slightly smaller than Ganymede, has the lowest
density of all the Galilean satellites, implying that it has large
amounts of water in its bulk composition. Its surface is darker than
the other Galilean satellites, although it is still twice as bright
as our Moon. This Voyager 2 image shows Callisto to have the most
heavily cratered and, therefore, the oldest surface of the Galilean
satellites, probably dating back to the period of heavy meteoritic
bombardment ending about four billion years ago.]
[Illustration: 3/6/79 350,000 km (217,000 mi)
The prominent concentric ring structure shown in this Voyager 1
four-picture mosaic of Callisto is believed to be a large impact
basin, similar to Mare Orientale on the Moon and Caloris Basin on
Mercury. The bright circular spot is about 600 kilometers (360
miles) across, and the outer ring is about 2600 kilometers (1560
miles) across. This is the first recognized basin in the Jovian
system and supports the assumption that Callisto’s surface is old.
The lack of high ridges, ring mountains, or a large central
depression suggests that the impacting body caused melting, some
flow, and shock waves, and that the refreezing occurred in time to
preserve the concentric shock rings.]
[Illustration: 7/7/79 390,000 km (245,000 mi)
Callisto is the most heavily cratered planetary body in our solar
system. In this Voyager 2 nine-frame mosaic, a special computer
filter was used to provide high contrast in the surface topography.
The impact structure visible at the upper right edge of the
satellite is smaller than the largest one found by Voyager 1 but
more detail is obvious; it is estimated that 15 concentric rings
surround the bright center. Many hundreds of moderate-sized craters
are also visible, a few with bright ray patterns. The limb is
smooth, which is consistent with Callisto’s icy composition.]
[Illustration: 3/6/79 200,000 km (125,000 mi)
This high-resolution image of Callisto, photographed by Voyager 1,
shows details of the large ring structure surrounding the remains of
the ancient impact basin visible on page 35. The surface area shown
in this image is at the right edge and slightly above the center of
the picture on page 35. The relatively undisturbed region on the
right shows the shoulder-to-shoulder large impact craters typical of
most of Callisto’s surface. A decrease in crater density toward the
center of the structure (to the left) is evident, and is caused by
the destruction of very old craters by the large impact that formed
the ring]