2. The new, close-up view from space


Space-age view of the planets

Space-age view of the planets

. A montage of planetary images taken with different spacecraft and presented, from top to bottom, in order of increasing distance from the Sun. They are Mercury (top) taken from Mariner 10, a Venus image from Magellan, the Earth seen by Galileo, with our Moon, a Viking mosaic image of Mars, Voyager 1 images of Jupiter and Saturn, and Voyager 2 views of Uranus and Neptune (bottom). The inner planets, closest to the Sun (Mercury, Venus, Earth and Mars) are roughly to scale to each other, and the outer planets, furthest from the Sun (Jupiter, Saturn, Uranus and Neptune) are also shown roughly to scale to each other. (Courtesy of JPL and NASA.)


The far side of the Moon

The far side of the Moon

. A view of the Moon never seen before the Space Age, and not visible from the Earth. This picture of the backside of the Moon was recorded by cameras aboard Apollo 16 in April 1972. The image is centered on the boundary between the lunar near side (upper left) and the Moon's hidden face (lower right). Three lunar maria are visible as dark patches on the near side. Clockwise from upper left: the Sea of Crises, the Border Sea and Smyth's sea. At lower right are the light-colored and heavily cratered highlands of the far side of the Moon. They contain almost none of the dark maria that characterize the side of the Moon that faces the Earth. (Courtesy of NASA.)


Lunar rover

Lunar rover

. The battery-powered lunar rovers, used in the last three Apollo missions, could carry two astronauts and all their equipment for thousands of meters across the lunar surface. Because there is no substantial atmosphere, water or weather on the Moon, both the rover and the footprints in the lunar soil may last for millions of years. By that time micrometeorites will have pitted the rover and erased the footprints. (Courtesy of NASA.)


Spaceshot of Mercury

Spaceshot of Mercury

. A photomosaic of Mercury's southern hemisphere produced from images acquired by Mariner 10 during its first encounter with the planet in March 1974. Mercury has a heavily cratered surface that resembles the lunar highlands. Bright rayed craters are also present on Mercury, as they are on the Moon. (Courtesy of JPL and NASA.)


Veiled Venus

Veiled Venus

. Bright opaque clouds of sulfuric acid wrap around Venus. The creamy yellow veil of clouds circulates once around the planet in only four Earth days, moving at speeds of up to 100 meters per second. Strong zonal winds combine with weaker poleward winds to carry the clouds in a slow spiral toward the poles. The thick cloudy atmosphere of Venus always blocks our view of the surface, and warms that surface to a torrid 730 degrees kelvin. (Courtesy of NASA.)


Saturn's realm

Saturn

. The magnificent rings of Saturn encircle the planet, never touching its cloud tops. The prominent gap in the rings is named the Cassini Division. The yellow-brown atmosphere of Saturn, shown here in enhanced color, has a banded structure, but it lacks Jupiter's bright zones and belts. Three icy satellites (Tethys, Dione and Rhea) are visible as small white spots against the darkness of space (bottom left), and another smaller satellite (Mimas) is visible against Saturn's cloud tops, just below the rings (right). Because of its rapid spin, Saturn has an oblong, egg-like shape, flattened at the poles and extended at the equator. (Courtesy of JPL and NASA.)


Neptune's dynamic atmosphere

Neptune

. After a journey of 12 years and 7 trillion (7 x 1012) meters, the Voyager 2 spacecraft captured this view of Neptune's Great Dark Spot (left center), accompanied by bright, white clouds that undergo rapid changes in appearance. The spot is as large as the Earth and about one third the diameter of the Great Red Spot of Jupiter. Another, smaller dark feature (bottom center) has a bright core. Internal heat drives strong winds on Neptune, moving at speed of up to 450 meters per second. The Voyager 2 images were sent by a small 20-watt transmitter. Traveling at the speed of light the radio signals took more than 4 hours to reach Earth. (Courtesy of JPL and NASA.)


Grand tour of Voyager 1 and 2

Grand tour of Voyager 1 and 2

. The flights of the two Voyager spacecraft through the solar system. Both spacecraft were launched in 1977 and flew past Jupiter in 1979, transmitting remarkable details of the giant planet's weather and the surfaces of its four largest satellites. Voyager 1 and 2 used the gravity of Jupiter to accelerate them on toward Saturn, providing close-up images of its rings and satellites in 1980-81. Saturn provided another gravity assist to propel Voyager 2 on to Uranus, in 1986, and from there on to Neptune in 1989. Voyager 1 was targeted differently at Saturn, sacrificing its grand tour for close views of the satellite Titan. Both spacecraft are now heading toward the edge of the solar system and will eventually leave it.


Giant world

Giant world

. Jupiter's clouded world with its alternating structure of light zones and dark belts. The two innermost Galilean satellites are also visible. Bright orange Io is seen just above the cloud tops, and icy-white Europa lies above it to the right. (Courtesy of JPL and NASA.)


Mozaic of Mars

Mozaic of Mars

. This computer-generated mosaic of Viking orbiter images of Mars shows three volcanoes as dark spots to the west (left), while the bottom center of the scene shows the entire Valles Marineris canyon system, from Noctis Labyrinthus (left) to the chaotic terrain (right). Outflow channels are found in the north (top), and a variety of clouds and hazes are also visible, especially near the edge. (Courtesy of Alfred S. McEwen, U.S. Geological Survey.)


Surface of Mars

Surface of Mars

. The Martian surface viewed from the Viking 1 lander on 3 August 1976. The Martian landscape resembles the rock-strewn deserts of the Earth. The wind-blown dunes create a gently rolling landscape. Drifting dust clings against the wind-eroded rocks and fills the sky. Mars is a cold and desolate world in which the silence is broken by the roar of winds, the hiss of dust, the rumble of mammoth landslides, and perhaps by outbursts of active volcanoes. (Courtesy of JPL and NASA.)


Venus unveiled

Venus unveiled

. A cloud-penetrating radar system on board the Magellan spacecraft has mapped the global landforms and features on Venus with a resolution of 120 meters, more completely than any planet including Earth. This hemisphere, centered at 180 degrees east longitude, shows the bright, planet-wide, equatorial highlands that contain towering volcanoes, long lava flows and deep faults and fractures. They run from lower left to upper right through Aphrodite Terra (left of center), a continent sized highland, through the bright highland Atla Regio (just right of center) to Beta Regio (far right and north). Dark areas correspond to terrain that is smooth on the scale of the radar wavelength (0.13 meters); bright areas are rough. The orange tint, based on color images taken by the Venera 13 and 14 landers, simulates the color of sunlight at ground level after being filtered through the planet's thick atmosphere and clouds. (Courtesy of JPL and NASA.)


Asteroids close up

Asteroids close up

. These images of the asteroids 951 Gaspra (left) and 243 Ida (right) were taken by the Jupiter-bound Galileo spacecraft on 29 October 1991 and 28 August 1993, respectively. Both objects have irregular, elongated shapes. The illuminated part of Gaspra is 18 thousand meters long, from lower left to upper right, and it contains an abundance of small craters. Ida is about 52 thousand meters in length, and is accompanied by a small moon (right center), named Dactyl. (Courtesy of JPL and NASA.)


Asteroids close up

Asteroids close up

. These images of the asteroids 951 Gaspra (left) and 243 Ida (right) were taken by the Jupiter-bound Galileo spacecraft on 29 October 1991 and 28 August 1993, respectively. Both objects have irregular, elongated shapes. The illuminated part of Gaspra is 18 thousand meters long, from lower left to upper right, and it contains an abundance of small craters. Ida is about 52 thousand meters in length, and is accompanied by a small moon (right center), named Dactyl. (Courtesy of JPL and NASA.)


Galileo's long flight to Jupiter

Galileo

. After launch in October 1989, the Galileo spacecraft used the gravity of the Earth and Venus to accelerate it on to its encounter with Jupiter, six years after launch. In its long, indirect flight path, Galileo was able to fly past two asteroids at close range, 951 Gaspra in October 1991 and 243 Ida in August 1993 (Fig. 2.14). It released an atmospheric probe just before arrival at Jupiter in December 1995; the main spacecraft continued to orbit the planet and examine its satellites for the next five years.


The black heart of Comet Halley

The black heart of Comet Halley

. The coal-black nucleus of Comet Halley is a dirty ball of ice, about the size of Paris or Manhattan. It is silhouetted against bright jets of water and dust that stream sunward (upper right) from at least three places that have been warmed by the Sun's radiation. In this projection, the nucleus measures 14.9 thousand meters by 8.2 thousand meters. This is a composite of images taken by the European Space Agency's (ESA's) Giotto spacecraft near its encounter with the nucleus of Comet Halley on 14 March 1986. (Courtesy of ESA.)


Lunar crater Timocharis

Lunar crater Timocharis

. Astronauts on board the Apollo 15 mission took this image of the medium-sized crater Timocharis, about 34 thousand meters across, in August 1971. The deposits and ejecta have been thrown radially outward by the meteorite impact that created the primary crater with its circular rim. Smaller secondary craters are located beyond the radial ejecta. (Courtesy of NASA.)


Cross-sectional anatomy of a crater

Cross-sectional anatomy of a crater

. An impacting meteorite excavates a circular crater that is almost 40 times the diameter of the meteorite. The depth of the crater is roughly one tenth its diameter, and the crater floor is depressed below the surrounding terrain. The explosion gauges out a circular hole, depositing material around its rim and ejecting debris radially outward in all directions. The surface rebounds from the impacting force of a large meteorite, creating a central peak in the floor of the biggest craters.


The Moon's Apennine mountains

The Moon

. The radial structure and steep inner slopes of these mountains (lower right) mark a section of the outer rim of the Imbrium Basin. The huge excavation was subsequently filled with lava to form the smooth Mare Imbrium and partially submerge the inner ring of mountains (upper left). The smaller circular craters include Timocharis (Fig. 2.16), about 34 thousand meters in diameter (center left) and the largest round structure Archimedes (upper center) with a diameter of 83 thousand meters. (Courtesy of the Lick Observatory.)


Mercury's Caloris Basin

Mercury

. A Mariner 10 mosaic image of the sunlit portion of the Caloris Basin. This multi-ring feature spans 1.34 million meters, and its rim is marked by rough mountainous blocks that rise up to 1,000 meters above the surrounding terrain. The collision resulted in a flat basin floor (left); it has been subsequently marked by smaller craters. (Courtesy of JPL and NASA.)


Mercury's Caloris impact

Mercury

. When an exceptionally large meteorite hit Mercury an estimated 3.85 billion years ago, it sent intense waves around the planet and through its core. They came to a focus on the opposite side of Mercury, disrupting the surface and producing hilly and lineated terrain there. The Caloris Basin was excavated at the impact site, and it now exhibits concentric waves that froze in place after the impact (Fig. 2.19).


Argyre region on Mars

Argyre region on Mars

. A mosaic of Viking images reveals the Argyre impact basin (left center) on Mars. The basin is a large circular expanse of light-colored plains about 800 thousand meters across. Its smooth floor is apparently filled with lava, like the Imbrium Basin on the Moon (Fig. 2.18). A rim of rugged mountains (left bottom) marks the basin edge, resembling the Apennine mountains on the Moon (Fig. 2.18). The adjacent terrain shows the heavily cratered surface of Mars that is typical of the planet's southern hemisphere. Argyre is the name of the "silver" island at the mouth of the Ganges River on Earth. (Courtesy of JPL, NASA and the U.S. Geological Survey.)


Aurelia impact crater on Venus

Aurelia impact crater on Venus

. The unusual crater shapes on Venus are illustrated in this Magellan radar image of the Aurelia crater. Like the large impact craters on the Moon, it contains a circular rim, terraced walls and a central peak. But unlike lunar craters, lobate flows emanate from the ejecta, and a sector of the flow is missing, apparently due to an oblique impact from the upper-left. Interaction with the dense, thick atmosphere on Venus caused the ejected debris to act like a fluid, producing the lacy, rounded lobes of ejecta. Crater Aurelia, which is 32 thousand meters in diameter, has been named in honor of the mother of Julius Caesar; apparently, Aurelia is also the name of Arnold Schwarzenegger's mother. (Courtesy of JPL and NASA.)


Jupiter's satellite Callisto

Jupiter

. This Voyager 1 image shows the heavily cratered surface of Callisto. Its icy crust is as rigid as steel, and it therefore retains the scars of an ancient bombardment by impacting meteorites. An exceptionally large meteorite sent waves rippling across the surface, like a rock dropped into a pond. The extensive system of concentric rings, extending about 1.5 million meters form the impact site (top center), is named Valhalla after the home of the Norse gods.. The impacting object apparently punctured the surface and disappeared. Today only the frozen, ghostlike ripples remain. Although there are very few large craters, the rest of Callisto is pockmarked with smaller impact craters that are flat for their size, and many of them have bright rims that resemble clean water ice splashed upon the dirtier surface ice. (Courtesy of JPL and NASA.)


Uranus' moon Miranda

Uranus

. The complex surface of Miranda, the innermost and smallest of the five major Uranian satellites, is seen at close range in this Voyager 2 image. It contains a rugged, higher-elevation terrain (right) and a lower, complex terrain with ridges, grooves and jagged cliffs. The numerous craters on the rugged, higher terrain indicate that it is older than the lower terrain. The largest impact craters shown here are abut 25 thousand meters across. The other relatively young and complex terrain is characterized by sets of bright and dark bands such as the distinctive "chevron" feature (top center). (Courtesy of JPL, NASA and the U.S. Geological Survey.)


Mauna Loa

Mauna Loa

. This radar image of the Mauna Loa volcano on the Big Island of Hawaii maps lava flows and other volcanic structures. Mauna Loa has erupted more than 35 times since the island was first visited by westerners in the early 1800s. The large summit crater, called Mokuaweoweo Caldera, is seen near the center of the image; this central depression was formed after lava flowed down the flanks of the volcano and magma was withdrawn inside it. If the height of the volcano is measured from its base on the ocean floor, Mauna Loa is the tallest mountain on Earth, rising almost 9 thousand meters above the ocean floor. (Courtesy of JPL and NASA.)


Nyiragongo

Nyiragongo

. The continent of Africa is being split apart by the pent-up pressure of hot, rising magma in numerous underlying hot spots along the Great Rift Valley. Volcanic outpourings like Nyiragongo fill the valley with lava as the rift slowly widens. (Courtesy of Bruce Coleman.)


Maat Mons

Maat Mons

. This three-dimensional perspective of Maat Mons on Venus was obtained from radar data taken with Magellan in October 1991. It is 8 thousand meters high, the second highest peak on the planet. Fresh, dark lava extends for hundreds of thousands of meters in the foreground, perhaps flowing from a relatively recent eruption. Maat Mons is a giant shield volcano similar in size and shape to the big island of Hawaii (Fig. 2.25). Maat is the name of the ancient Egyptian goddess of truth and justice, and Mons is the Latin term for "mountain". The orange tint simulates the color of sunlight at ground level after filtering by the dense, thick atmosphere. (Courtesy of JPL and NASA.)


Shield volcanoes on Venus

Shield volcanoes on Venus

. Approximately 200 small volcanoes, ranging in diameter from 2 thousand to 12 thousand meters, can be identified in this Magellan radar image. They are shield-type volcanoes constructed mainly from eruptions of fluid lava flows similar to those that produce the Hawaiian Islands and sea floor volcanoes on Earth. These small volcanoes are the most abundant geological features on the surface of Venus, believed to number in the hundreds of thousands and perhaps millions. (Courtesy of JPL and NASA.)


Pancake domes on Venus

Pancake domes on Venus

. These seven volcanic domes were discovered in Magellan's radar images. They all have round shapes that are about 25 thousand meters across, and steep sides that are less than 750 meters high. Their central vents may be lined up along a crack in the surface. These domes are interpreted as very thick, stiff and sluggish lava flows, rather than the fluid and runny type. Eruptions of the pasty, viscous lava, coming from a central vent on a relatively level surface, would form the circular, flattened shapes that resemble giant pancakes. Since there is little or no erosion by wind or water on Venus, newer pancakes look much the same as the ones on which they are superimposed. (Courtesy of JPL and NASA.)


Olympus Mons

Olympus Mons

. A mosaic of the towering Martian volcano Olympus Mons, using data obtained from the Viking 1 orbiter in the late 1970s. It is the largest known volcano in the solar system, rising 27 thousand meters and spreading over 600 thousand meters at its base. The lava flows on the gentle slopes of this volcano are relatively young, averaging only about 30 million years old. The summit caldera, or central depression, is a composite of as many as seven roughly circular depressions that probably formed by recurrent collapse when magma was withdrawn from within the volcano. The caldera is almost 3 thousand meters deep and up to 70 thousand meters across. The volcano is surrounded by a well defined scarp, or cliff, that is up to 6 thousand meters high. Much of the plains surrounding the volcano are covered by rigid and grooved aureole, the Latin term for "circle of light". Mons is the Latin term for "mountain". Mount Olympus, the highest mountain in Greece, is the home of the gods in Greek mythology. (Courtesy of JPL, NASA and the U.S. Geological Survey.)


Ceraunius Tholus

Ceraunius Tholus

. This Viking 1 image portrays the large volcano, Ceraunius Tholus, which is 115 thousand meters in diameter. A 2-thousand-meter wide channel extends from the summit caldera down the flanks of the volcano into an input crater in the adjacent plains. Smaller channels are just visible elsewhere on the flanks. The surrounding region (left) includes intensely fractured terrain. The term tholus means "small domical mountain or hill, and ceraunius means "thunderclap". Ceraunius tholus is named for the Ceraunii mountains on the coast of Epirus, Greece. (Courtesy of JPL and NASA.)


Apollinaris Patera and Tyrrhena Patera

Apollinaris Patera and Tyrrhena Patera

. These Martian volcanoes, imaged by cameras on Viking 1, are of the patera type, with low summits and broad flows. The summit caldera of Apollinaris Partera (left) is 80 thousand meters wide, and the lava flows on its flanks occurred, on average, about a billion years ago. Tyrrhena Patera (right) is low-lying, fractured and highly eroded, with an estimated age of about 2 billion years. The caldera, about 12 thousand meters across, is surrounded by a fracture ring about 45 thousand meters in diameter. Several channels extend outward as much as 200 thousand meters from the volcano center. The volcano could be comprised largely of ash flows, in contrast to the towering, younger shield volcanoes which are mostly lava (Fig. 2.30). In Greek mythology, Apollo is the god of prophecy, sunlight, music and healing, and patera is an ancient Roman term meaning a "broad flat saucer or dish". The Tyrrhenian Sea is located between Italy and Sicily. (Courtesy of JPL and NASA.)


Apollinaris Patera and Tyrrhena Patera

Apollinaris Patera and Tyrrhena Patera

. These Martian volcanoes, imaged by cameras on Viking 1, are of the patera type, with low summits and broad flows. The summit caldera of Apollinaris Partera (left) is 80 thousand meters wide, and the lava flows on its flanks occurred, on average, about a billion years ago. Tyrrhena Patera (right) is low-lying, fractured and highly eroded, with an estimated age of about 2 billion years. The caldera, about 12 thousand meters across, is surrounded by a fracture ring about 45 thousand meters in diameter. Several channels extend outward as much as 200 thousand meters from the volcano center. The volcano could be comprised largely of ash flows, in contrast to the towering, younger shield volcanoes which are mostly lava (Fig. 2.30). In Greek mythology, Apollo is the god of prophecy, sunlight, music and healing, and patera is an ancient Roman term meaning a "broad flat saucer or dish". The Tyrrhenian Sea is located between Italy and Sicily. (Courtesy of JPL and NASA.)


Volcanic activity on Io

Volcanic activity on Io

. Voyager 1 captured this view of numerous volcanoes on Io on 13 July 1979. In contrast to Jupiter's satellite Callisto (Fig. 2.23), there are no impact craters on the surface of Io. Its volcanoes are continually resurfacing the satellite, keeping it young and erasing all signs of any impact craters. (Courtesy of JPL and NASA.)


Lava flows on Jupiter's satellite Io

Lava flows on Jupiter

. Numerous calderas and lava flows are located in this Voyager 1 image mosaic of Io's volcanic plains. They are punctuated by dark snake-like tendrils of red, brown and black lava flows that are rich in sulfur. The bright whitish patches probably consist of freshly deposited sulfur dioxide frost. This scene is about 2.1 million meters long, indicating that the slopes of active volcanoes stretch as far as 200 thousand meters from the hot, black calderas into the cooler surrounding terrain. (Courtesy of JPL, NASA and the U.S. Geological Survey.)


Culann Patera

Culann Patera

. One of the most colorful volcanic centers on Io is shown in this picture, constructed from images taken on 25 November 1999 through the red, green, and violet filters of a camera on board Galileo. Various colored lava flows spill out of the caldera on all sides. Unusual dark red flows to the south east (bottom right) may be sulfur flows or silicate flows whose surfaces have been modified. The diffuse red material around the caldera is believed to be a compound of sulfur deposited from a plume of gas. Culann is the Celtic smith god, and patera is a Roman term meaning a "broad flat saucer or dish". (Courtesy of JPL, NASA and LPL at the University of Arizona.)


Triton's dark plumes and streaks

Triton

. This image of the south polar terrain on Triton reveals about 50 elongated dark plumes, or "wind streaks" on the moon's highly reflective surface. The plumes originate at very dark spots, generally several thousand meters across, probably marking vents where nitrogen gas was driven outward in geyser-like eruptions from beneath the surface. Winds in Triton's thin, nitrogen atmosphere may have carried the dark erupted material along, depositing it in the elongated streaks. This image was taken on 25 August 1989 from Voyager 2. (Courtesy of JPL and NASA.)


Earth, the water planet

Earth, the water planet

. Almost three quarters of the Earth's surface is covered by water, as suggested by this view of the North Pacific Ocean. Earth is the only planet in the solar system where substantial amounts of water exist in all three possible forms - gas (water vapor), liquid and solid (ice). Here white clouds of water ice swirl near Alaska; the predominantly white ground area, consisting of snow and ice, is the Kamchatka Peninsula of Siberia. Japan appears near the horizon. From this orientation in space, we also see both the day and night sides of our home planet. (Courtesy of NASA.)


Outflow channels

Outflow channels

. A Viking 1 image of the Ares Vallis region shows dry river beds produced by past flows of liquid water. Catastrophic floods must have carved out these outflow channels deep in the Martian surface, creating streamlined hills, scoured floors, and large teardrop-shaped islands where flowing water encountered an obstacle. Ares is the Greek god of war; the Roman equivalent is Mars. (Courtesy of Michael H. Carr, U.S. Geological Survey, and NASA.)


Global topography of Mars

Global topography of Mars

. The laser altimeter on Mars Global Surveyor yielded this precise global relief map of Mars, with the south pole (S) at the bottom and the north pole (N) at the top. The red areas in the southern hemisphere are high regions, about four thousand meters above the average surface height, and the blue regions of the northern hemisphere are low places, about four thousand meters below the average height. Since it is mainly downhill from south to north, ancient flood waters must have flowed in that direction, within the blue-colored outflow channels to the east (right) of Valles Marineris and to the west (left) of Olympus Mons, perhaps emptying into the northern lowlands and forming an ancient ocean there. (Courtesy of JPL and NASA.)


Layered rocks on Mars

Layered rocks on Mars

. These images from Mars Global Surveyor reveal hundreds of layers of similar thickness, texture and pattern that have been exposed in an impact crater in western Arabia Terra (left) and in a canyon located in southwestern Candor Chasma (right) of the Valles Marineris. The numerous, uniform deposits resemble regularly-layered, sedimentary rocks found on Earth. The Martian features could therefore be due to sediments that settled out of liquid water in ancient lakes or shallow seas a few billion years ago. The material might alternatively be due to deposits of airborne dust settling out of the atmosphere, that were later buried and compacted. Arabia is a peninsula of southwestern Asia, bordering the Persian Gulf, the Arabian Sea , and the Red Sea; terra means "extensive land mass"; candor is Latin for "glossy whiteness or sincerity", and chasma is "a deep, elongated, steep-sided depression". (Courtesy of JPL, NASA and Malin Space Science Systems.)


Layered rocks on Mars

Layered rocks on Mars

. These images from Mars Global Surveyor reveal hundreds of layers of similar thickness, texture and pattern that have been exposed in an impact crater in western Arabia Terra (left) and in a canyon located in southwestern Candor Chasma (right) of the Valles Marineris. The numerous, uniform deposits resemble regularly-layered, sedimentary rocks found on Earth. The Martian features could therefore be due to sediments that settled out of liquid water in ancient lakes or shallow seas a few billion years ago. The material might alternatively be due to deposits of airborne dust settling out of the atmosphere, that were later buried and compacted. Arabia is a peninsula of southwestern Asia, bordering the Persian Gulf, the Arabian Sea , and the Red Sea; terra means "extensive land mass"; candor is Latin for "glossy whiteness or sincerity", and chasma is "a deep, elongated, steep-sided depression". (Courtesy of JPL, NASA and Malin Space Science Systems.)


Jupiter's satellite Europa

Jupiter

. Dark streaks mark Europa's smooth surface, forming a spidery, veined network in this Voyager 2 image taken on 9 July 1979. In contrast to Jupiter's satellite Callisto (Fig. 2.23), Europa has very few impact craters; the absence of craters suggests that the ice crust is relatively young. Internal stresses apparently fractured its icy mantle, producing intersecting cracks that extend for millions of meters, but reach depths of less than 100 meters. The fractures may have been filled by liquid water gushing out from a global ocean in the satellite's interior, warmed by tidal heating. (Courtesy of NASA and JPL.)


Europa in color

Europa in color

. A composite, color-enhanced image of the Minos Linea region of Jupiter's moon Europa, taken on 28 June 1996 by imaging cameras on Galileo. The icy plains, shown here in bluish hues, reflect different amounts of light, probably as the result of differences in the sizes of the ice grains. The long red cracks in the ice could mark the sites of liquid water oozing out from the warm interior of Europa. The area covered in this image is about 1.26 thousand meters across. In Greek mythology, Minos is the son of Zeus and the king of Crete, who kept a monster named minotaur in a labyrinth. Linea is a "dark or bright elongate marking". (Courtesy of JPL, NASA and PIRL at the University of Arizona.)


Jupiter's satellite Ganymede

Jupiter

. Large dark blocks are frozen within the icy surface of Ganymede. They are believed to be part of the original crust of the satellite, resembling frozen-over continents floating on a background of translucent ice. The brilliant white material that surrounds some craters is probably clean water ice or bright snow that was splashed out from inside the satellite. The enhanced color of this Galileo image of Ganymede, taken on 29 March 1998, also reveals the two predominant terrain on Ganymede, bright grooved terrain and older, dark furrowed areas. The violet hues at the poles may be the result of small particles of frost. (Courtesy of JPL, NASA, and DLR, the German aerospace center.)


Saturn's satellite Enceladus

Saturn

. The bright, smooth surface of Enceladus, shown in this Voyager 2 image obtained on 25 August 1981, reflects almost 100 percent of the incident sunlight, making it one of the most reflective objects in the solar system. When viewed up close, part of its surface is scarred with impact craters, and such impacts might have released liquid water from the satellite's interior. Other parts of the surface contain cracks and grooves, suggesting that internal stresses that may have also discharged water that froze into smooth ice. (Courtesy of JPL and NASA.)