9. Jupiter: a giant primitive planet


Banded wind-blown clouds on Jupiter

Banded wind-blown clouds on Jupiter

. The traditional nomenclature of Jupiter’s light and dark bands of clouds (left) is given in abbreviated form (center). The dark bands are called belts, denoted by “B”, the light bands are known as zones, or “Z”, and the rest of each name is based on climatic regions at the corresponding latitudes on Earth. North, letter “N” is at the top, and south, denoted by “S”, is at the bottom. The equatorial, or “E”, bands are in the middle, the tropical, “TR”, bands on each side of the equator, and the temperate, “T”, ones at mid-latitudes. Far northern latitudes are denoted by “NN”, far southern latitudes by “SS”, and the polar regions by “P”. The image of Jupiter (right) was taken from the Cassini spacecraft on 7 December 2000, when Jupiter’s moon Europa cast a shadow on the planet. The arrows point in the direction of wind flow, and their length corresponds to the wind velocity, which can reach 180 meters per second near the equator. (Image courtesy of NASA and JPL.)


Jupiter’s turbulent clouds

Jupiter’s turbulent clouds

. This image accentuates the detailed cloud structures and movements at the top of Jupiter’s atmosphere. It was taken from the Cassini spacecraft at a red wavelength where methane gas absorbs light at high altitudes within the ammonia and ammonium hydrosulfide cloud layers. A polar stratospheric haze (bottom) makes Jupiter bright near the south pole. (Courtesy of NASA, JPL, CICLOPS and the University of Arizona.)


Great Red Spot

Great Red Spot

. The largest and oldest known weather system in the solar system is Jupiter’s Great Red Spot. The spot's diameter is twice that of Earth, and one-sixth the diameter of Jupiter itself. The red vortex swirls in the counterclockwise direction in Jupiter’s southern hemisphere, showing that it is a high-pressure anti-cyclone. It has been observed for centuries, probably ever since astronomers turned the first telescopes toward the giant planet. Some small eddies are sucked into the Great Red Spot, helping to sustain it, while other eddies roll around the perimeter, probably reinforcing its circulation. A long-lived white oval is seen just below the Red Spot, also rotating in the anti-cyclone manner. This oval is one of three systems that formed in 1939. They had slowly contracted in length and drifted about the planet approaching and moving apart. The Voyager 1 spacecraft took this image on 25 February 1979. (Courtesy of NASA and JPL.)


Temperature and pressure at Jovian cloud levels

Temperature and pressure at Jovian cloud levels

. The fading radio signals when the Voyager 1 and 2 spacecraft passed behind Jupiter in 1979 revealed the temperatures (bottom axis) and pressures (right axis) in its upper atmosphere. The temperature reaches a minimum of about 114 degrees kelvin at a level called the tropopause where the atmospheric pressure is 0.1 bars, or 100 millibars. By way of comparison, the pressure of the Earth’s atmosphere at sea level is 1.0 bar. The altitudes (left axis) are relative to the 0.1 bar level, and the dots are spaced to indicate tenfold changes in pressure. Solar radiation causes the temperature to increase with height just above the tropospause. At lower levels, the temperature and pressure increases systematically with depth. Three expected clouds layers of ammonia, NH3, ammonium hydrosulfide, NH4SH, and water ice, H2O, are shown. The altitudes of the predicted cloud layers are based on a gaseous mixture that is of solar composition. An increase of the abundance of a condensable gas by a factor of three would lower the altitude of the cloud base by about 10 kilometers.


Jupiter’s ammonia ice clouds

Jupiter’s ammonia ice clouds

. A cloud of ammonia ice (light blue) is shown at the northwest (upper left) of the Great Red Spot (middle), inside its turbulent wake. The cloud was most likely produced by powerful updrafts of ammonia-laden air from deep within Jupiter’s atmosphere. Reddish-orange areas show high-level clouds, yellow regions depict mid-level clouds, and green areas correspond to lower-level clouds. Darker areas are cloud-free regions. Light blue depicts regions of middle-to-high altitude ammonia ice clouds. This near-infrared image was taken on 26 June 1996 from the Galileo spacecraft. (Courtesy of NASA and JPL.)


Thunderstorm on Jupiter

Thunderstorm on Jupiter

. Instruments aboard the Galileo spacecraft determined the altitudes of this tall, thick thunderstorm (mottled white region), which towers 25 kilometers above the surrounding clouds and extends 50 kilometers below them (red base). On Jupiter, water is the only substance that can form a cloud at this depth, where the pressure is four or five times the sea-level pressure on Earth. Other towering thunderstorms on Jupiter have been shown to produce powerful lightening bolts, suggesting that these clouds contain falling raindrops and rising air columns. Massive storm cells like these probably transport heat from Jupiter’s interior into its long-lived cloudy weather patterns of bands and ovals. Similar water-rich thunderstorms with lightning exist on Earth, but their Jovian counterparts are about five times broader and taller. (Courtesy of NASA, JPL, Cornell University, and the California Institute of Technology.)


Hot spot on Jupiter

Hot spot on Jupiter

. The dark region near the center of this image is an equatorial “hotspot”, similar to the site where the Galileo spacecraft parachuted a probe into Jupiter’s atmosphere in December 1995. Jupiter has many such regions, and they continually change, so the probe could not be targeted to either hit or avoid them. The dark hotspot is a clear gap in the clouds where infrared radiant energy from the planet’s deep atmosphere shines through. Although hotter than the surrounding clouds, these so-called “hotspots” are still colder than the freezing temperature of water. Dry atmospheric gas may be converging and sinking in these regions, maintaining their cloud-free appearance. The bright ovals, shown in other parts of this image, may be examples of upwelling moist air. The images combined in this mosaic were taken on 17 December 1996 from the Galileo spacecraft. (Courtesy of NASA and JPL.)


Inside Jupiter

Inside Jupiter

. Giant Jupiter has a thin gaseous atmosphere covering a vast global ocean of liquid hydrogen. At the enormous pressures within Jupiter’s interior, the abundant hydrogen is compressed into an outer shell of liquid molecular hydrogen and an inner shell zone of fluid metallic hydrogen. The giant planet probably has a relatively small core of ice and rock.


Giant Red Spot and Galilean satellites

Giant Red Spot and Galilean satellites

. This “family portrait” includes the edge of Jupiter with its Great Red Spot and on the same scale the planet’s four largest moons, known as the Galilean satellites. From top to bottom the moons are Io, Europa, Ganymede and Callisto. The Great Red Spot is larger than one Earth diameter from north to south, while Europa is about the size of Earth’s Moon. Ganymede is the largest moon in the solar system. (Courtesy of NASA and JPL.)


Internal structures of the Galilean satellites

Internal structures of the Galilean satellites

. The interior characteristics of Jupiter’s four largest moons have been inferred from gravitational and magnetic field measurements from the Galileo spacecraft. The satellites are shown according to their actual relative size, and compared with those of the Moon and Mercury (horizontal bars). With the exception of Callisto, the metal, rock and ice have separated, or differentiated, into distinct layers. Io, Europa and Ganymede all have metallic, or iron and nickel, cores surrounded by rock, or silicate, shells. Io’s rocky shell extends to the surface, while outer layers of water, in ice or liquid form, surround Europa and Ganymede. The surface of Io contains numerous active volcanoes, and Europa’s thin, frozen crust of water ice probably covers a liquid ocean. Callisto seems to have a relatively uniform internal mixture of ice and rock. (Courtesy of NASA and JPL.)


Volcanic deposits on Io

Volcanic deposits on Io

. Massive eruptions continually disfigure the surface of Jupiter’s volcanically active moon Io. Its entire surface is peppered with volcanoes, some of which are erupting as you read this. A prominent, bright red ring, 1400 kilometers across, surrounds the volcano Pele, marking the site of sulfur compounds deposited by its volcanic plumes. A dark circular area intersects the upper-right part of the red ring, 400 kilometers in diameter, that surrounds another volcanic center named Pillan Patera. The dark deposits suggest a high silicate content. Deposits of sulfur dioxide frost appear white and gray in this view, while other sulfurous materials probably cause the yellow and brown shades. Pele is the Hawaiian goddess of the volcano, and Pillan Patera is named for the Araucanian thunder, fire and volcano god. This image was taken on 19 December 1997 from the Galileo spacecraft. (Courtesy of NASA and JPL.)


Volcanoes erupting on Io

Volcanoes erupting on Io

. Several volcanic plumes are shown in this diagram, derived from Galileo observations of Io when Jupiter eclipsed the moon. Bright blue glows were observed emanating from the volcanic plumes, including the volcano Prometheus whose diffuse glow extended 800 kilometers from the edge of Io. The glow is probably molecular emission from sulfur dioxide, denoted SO2, known to be abundant in volcanic plumes. The eruptive centers are named after mythological figures such as Amirani, the Georgian god of fire, Culann, the Celtic smith god, Prometheus, the Greek god of fire, and Zamana, the Babylonian Sun, corn and war god. (Courtesy of PIRL, University of Arizona,)


Eruption of Pele

Eruption of Pele

. During its flyby on 4-5 March 1979, the Voyager 1 spacecraft captured this image of an active volcano on Jupiter’s moon Io. The volcano has been named Pele, after the Hawaiian goddess of the volcano. Its erupting plume is visible at the upper right, rising to a height of about 300 kilometers above the surface in an umbrella-like shape. The plume has been ejected from the triangular-shaped blue and white complex of hills (right center). In this enhanced color image, we see the plume fallout as concentric brown and yellow rings, the largest stretching across 1400 kilometers and covering an area the size of Alaska. Pele remained active for at least two decades, and new deposits from its plumes have been imaged by the Galileo spacecraft in the late 1990s (Fig. 9.11). (Courtesy of NASA, JPL and the U.S. Geological Survey.)


Fountain-like eruptions on Io

Fountain-like eruptions on Io

. Voyager 1 discovered plumes of active volcanoes on Jupiter’s moon Io when the spacecraft flew by the planet on 4-5 March 1979 (left). A computer simulation of a volcanic eruption on Io shows the fountain-like trajectories of the volcanic plume (rightleft), and Nicholas M. Schneider, Lunar and Planetary Laboratory, Tucson (right).]


Tidal flexing of Io

Tidal flexing of Io

. Due to an orbital resonance with nearby Europa, Jupiter’s satellite Io has a noncircular orbit. The forced eccentricity makes Io travel at different velocities along its orbit and the side facing Jupiter nods back and forth slightly, as seen from the planet. Although only half a degree in extent, this movement causes varying tidal forces inside the satellite, flexing it in and out like squeezing an exercise ball with your hand. This, in turn, generates internal friction and heat, leading to the active volcanoes seen on Io with instruments aboard the Voyager 1 and 2 and Galileo spacecraft. In this drawing, Io’s size is exaggerated when compared with Jupiter.


The sodium cloud

The sodium cloud

. Io’s neutral sodium cloud (left) as seen from the Earth, shown together with Jupiter (center) and a schematic drawing of Io’s orbit to scale. Excited sodium atoms that come from Io (location denoted by a cross) emit radiation at spectral lines that can be detected from ground-based optical telescopes. These observations of the sodium cloud were made with the 0.61-meter (24-inch) telescope at Table Mountain Observatory in California; the image of Jupiter was taken at a different time and place. (Courtesy of Bruce Goldberg and Glenn Garneau, Jet Propulsion Laboratory.)


Flux tube and plasma torus

Flux tube and plasma torus

. An electric current of five million amperes flows along Io’s flux tube. It connects Io to the upper atmosphere of Jupiter, like a giant umbilical cord. The plasma torus is centered near Io’s orbit, and it is about as thick as Jupiter is wide. The torus is filled with energetic sulfur and oxygen ions that have a temperature of about 100 thousand degrees kelvin. Because the planet’s rotational axis is tilted with respect to the magnetic axis, the orbit of the satellite Io (dashed line) is inclined to the plasma torus.


Europa’s frozen, disrupted surface

Europa’s frozen, disrupted surface

. Numerous, old impact craters have been erased from Jupiter’s moon Europa, perhaps by fresh ice produced along cracks in the thin crust or by cold glacier-like flows. The number of impact craters found on the bright, smooth surface indicates an age of approximately 100 million years. The thin, water-ice crust has undergone extensive disruption from below (upper left). Two irregular, chaotic dark features (just below center) were most likely formed when liquid water or warm ice welled up from underneath Europa’s icy shell. These dark spots, technically called macula, are named Thera and Thrace after two places in Greece that Cadmus stopped in his search for Europa. This image, approximately 675 kilometers across, was taken from the Galileo spacecraft on 20 February 1997. (Courtesy of NASA and JPL.)


Broken ice on Europa

Broken ice on Europa

. Dark, linear crack-like features (top right) extend for thousands of kilometers across Jupiter’s moon Europa. They are believed to have formed when the satellite’s thin, icy crust fractured, separated and was filled by a dirty slush from a possible ocean below. The long cracks were most likely caused by tides raised on Europa by the gravitational pull of Jupiter. This image, about 770 kilometers wide, was taken from the Galileo spacecraft on 27 June 1996. (Courtesy of NASA and JPL.)


Europa under stress

Europa under stress

. When viewed at high resolution, many sets of parallel and crosscutting ridges and fractures are detected on Jupiter’s moon Europa. These features are the frozen remnants of surface tension and compression, probably produced by heating and upwelling from below. The icy crust has also been broken into plates or “rafts”, ranging up to 13 kilometers across, which have separated and moved into new positions, somewhat like pack ice in the Earth’s polar seas. Soft ice or liquid water below the surface most likely lubricated the moving ice rafts on Europa at the time of disruption. This image, approximately 42 kilometers across, was taken from the Galileo spacecraft on 20 February 1999. (Courtesy of NASA and JPL.)


Ganymede

Ganymede

. The surface of Ganymede, Jupiter’s largest satellite, includes impact craters that suggest an age of a few billion years. The bright rays that surround many craters (lower left) probably consist of icy material thrown out by the impacts. Sinuous ridges and grooves traverse the surface (lower right) most likely caused by deformation of the thick ice crust from below. The Voyager 1 spacecraft took this image, about one thousands kilometers wide, on 5 March 1979. (Courtesy of NASA and JPL.)


Ganymede close up

Ganymede close up

. The bright icy crust on Jupiter’s moon Ganymede contains both young and old terrain with bright grooves, caused by internal stress, and craters due to external impact. The youngest terrain (center) is finely striated and relatively lightly cratered. The oldest terrain (right) is rolling and relatively heavily cratered. The highly deformed grooved terrain (left) is of intermediate age. This image, approximately 89 kilometers across, was taken from the Galileo spacecraft on 20 May 2000 (Courtesy of NASA and JPL.)


Varied terrain on Ganymede

Varied terrain on Ganymede

. The surface of Jupiter’s largest moon, Ganymede, contains old, dark polygonal blocks frozen within its icy surface. They resemble brown, frozen-over continents floating on a background of translucent ice. The ancient blocks have apparently separated like the moving pieces of a huge mosaic or giant jigsaw puzzle, perhaps because of satellite’s crust has expanded. The brilliant, relatively young white material that surrounds some craters is probably fresh, clean water ice that splashed out from inside the satellite. The rays extending from the bright crater in the northern (top) part of this picture are up to 500 kilometers long. This image was acquired from the Voyager 1 spacecraft on 5 March 1979 (Courtesy of NASA and JPL.)


Callisto

Callisto

. Jupiter’s outermost large moon Callisto exhibits more craters and older terrain than seen on any of the Galilean satellites. It is a battered world, pockmarked with impact craters dating back to the final stages of planetary formation over 4 billion years ago. Because Callisto’s icy surface is as rigid as steel, it retains the scars of an ancient bombardment similar to the one that created the heavily cratered terrain on the Moon and Mercury. The bright regions probably contain fresh crustal ice thrown out from relatively young impact craters, and splashed upon the older, dirtier surface ice. This image was acquired in May 2001 from the Galileo spacecraft. (Courtesy of NASA, JPL and DLR – the German Aerospace Center.)


Dark material and few small craters on Callisto

Dark material and few small craters on Callisto

. A dark, mobile blanket of fine material covers Callisto’s surface, sometimes collecting within crater walls. While Jupiter’s moon Callisto is saturated with large impact craters, it has fewer very small craters when compared with the Moon and Mercury. One explanation is that the smaller craters have been filled by dark material that has moved down surface slopes. An alternative explanation for the paucity of little craters on Callisto is that there were fewer small impacting objects in its vicinity when compared with the amount within the inner solar system. This image, about 74 kilometers across, was taken from the Galileo spacecraft on 17 September 1997. (Courtesy of NASA and JPL.)


Jupiter’s main ring and halo

Jupiter’s main ring and halo

. Jupiter’s bright, flat main ring (bottom) is a thin strand of material encircling the planet with an outer radius of 128.94 thousand kilometers, or about 1.8 Jovian radii, located very close to the orbit of the giant planet’s small moon Adrastea, at 128.98 thousand kilometers. The brightness of the main ring drops markedly very near the orbit of another moon, Metis. A faint mist of particles, known as the ring halo, surrounds the main ring and lies above and below it (top). The vertically extended halo is unusual for planetary rings, which are normally flattened into a thin plane by gravity and motion. The halo probably results from the “levitation” of small particles that are pushed out of the main ring plane by electromagnetic forces. These images were obtained from the Galileo spacecraft on 9 November 1996 when it was in Jupiter’s shadow, looking back toward the Sun. The rings of Jupiter proved to be unexpectedly bright when seen with the Sun behind them, just as motes of dust or cigarette smoke brighten when they float in front of a light. A third gossamer ring, which consists of two components, is not shown here; it lies beyond the main ring, at greater distances from Jupiter. (Courtesy on NASA and JPL.)


Summary Diagram.

Summary Diagram.

. Summary Diagram.