The Jupiter System

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		Jupiter, Ganymede, and Callisto at 47 million km This image of Jupiter, Ganymede and Callisto was taken while Voyager 1 was a little over a month away (closest approach was on March 5). Ganymede is at right center and Europa is at the top right. Ganymede is larger than Mercury and looks to be composed of a mixture of rock and water ice. Europa, slightly smaller than the Moon, exhibits a very bright surface. Jupiter is 71,492 km in diameter and north is at 11:30. (Voyager 1, P-20938)
		The Great Red Spot The Great Red Spot is a gigantic long-lived storm, similar to a hurricane. The red color is caused when reddish material is moved by the storm toward the surface, and comes and goes, though the storm itself has been observed since telescopic observations began. The spot is an oval with major and minor axes of roughly 20,000 and 13,000 Km. making it somewhat larger than the Earth. This picture is a mosaic of several Galileo images.
		Southeast of the Great Red Spot on Jupiter This Voyager 1 image shows clouds of Jupiter to the southeast of the Great Red Spot. The colors have been photographically exaggerated to enhance subtle variations in color and shading in order to bring out details of the cloud structure and atmospheric dynamics. (Voyager 1, P-21224)
		Jupiter and Io This image was taken by the Cassini spacecraft on January 1, 2001, while en route to Saturn. It shows Io against a backdrop of the clouds of Jupiter. The weird surface of Io is clearly noticeable. The diameter of Io is approximately the distance from Los Angeles to Boston, which gives some idea of the scale of the Jovian weather systems below. NASA uses the gravity of planets like Jupiter to accelerate and alter the courses of spacecraft heading to more distant worlds, in this case allowing a "free" visit to Jupiter
		Crescent Jupiter and Io This image was taken by the Cassini spacecraft on January 3, 2001, as it was departing Jupiter. The reddish area on Jupiter near Io is not the Great Red Spot.
		Jupiter's satellite Io This is the famous "Pizza Picture" of Io from Voyarer 1. The colors have been enhanced some, and the atmospheric haze and volcanic plumes have been added in from an overexposed image. Io is about 3,600 km in diameter. It is the most volcanically active body in the solar system, usually sporting several active volcanoes at any time that constantly alter the landscape. In the image, dark round spots usually mark the volcanic vents and the ovals surrounding them are eruption deposits. Sulfur and sulfur compounds produce the exotic colors. The vulcanism of Io is produced by the combined tides of Jupiter and the other moons, which bend and heat the solid crust.
		False Color Image of Io and Jupiter This image of Io against the clouds of Jupiter was produced from separate Galileo spacecraft images through violet, green, and near-infrared filters. Jupiter is dark in the near infrared, and the lack of a red image combined with this makes Jupiter look blue, but these are very near the actual colors of Io, except fot the bright infrared spots near some of the volcanoes, which would not be as prominant in natural color. By shear coincidence, this is nearly the same face of Io as that seen in the "Pizza Picture," so it is possible to see common and altered features.
		Volcanic Caldera and Flows on Io This image shows volcanic calderas on Jupiter's moon Io. The caldera may be venting gasses, seen as the light patch at left center in this picture. The dark areas on the caldera floor are thought to be molten basalt, similar to the lava on Earth. The image was taken as Voyager 1 approached Io at a distance of about 130,000 km. (Voyager 1, P-21286)
		Ionian Volcanic Eruption at Tvashtar Catena This Galileo image shows a volcanic eruption in progress. It was produced by merging an infrared image showing the lava flow with a natural color image of the region, in order to produce a simulation of what would actually be seen with the naked eye at Io. Simply producing a true-color photograph was not feasable because of data transmission constraints and the fact that the color filters that produce good photographs are not usually the ones that produce the best scientific data.
		Io Sodium Cloud Ionized sodium produces characteristic colors which can be isolated, imaged, and used to track eruptions that contain this metal. In this case, nearly everything yellow is sodium, while red represents all other sources of light. The crescent at the left is the side of Io illuminated by reflected light from Jupiter - the moon itself is in Jupiter's shadow. The bright spot on the right of the disk is an eruption of the volcano Prometheus, and the gas can be seen escaping into space. The red spot below and to the left of Prometheus in this image is the volcano Pele, which was not erupting nearly as much at the time.
		Aurorae on Io When high-speed charged particles trapped in Jupiter's powerful magnetic field slam into Io's atmosphere of volcanic exhaust, they energize the atmospheric atoms and they emit light. The process is similar to that by which electricity produces light in flourescent bulbs and to that which produces the aurorae borealis and australis on Earth. A "normal" view of Io is shown in the same orientation for comparison. The right and left limbs in this image point toward (0°) and away from Jupiter, respectively, and the brighter glows there may indicate greater overall outgassing in those areas, where the tidal effect of Jupiter is greatest.
		Color image of Jupiter's moon Europa This image was captured on September 7, 1996, at a range of 677,000 kilometers (417,900 miles) by the Galileo spacecraft. Complex linear grooves and fractures are apparent in this view, which shows features as small as a few kilometers in diameter. The moon itself has a diameter of about 3160 km. The surface is made of water ice with salty impurities near the cracks believed to come from a subsurface ocean. The large crater, Pwyll, is named for a hero of the Welsh legends called The Mabinogion.
		Double Ridges, Pits, and Smooth Terrain on Europa This false color Galileo mosaic of a region about 800 x 350 Km in area displays some of the characteristic features of this moon. Relatively smooth terrain is criscrossed by double cracks that appear to have deposited yellow material on the surface. There are also small pits and larger pits that seem to include rougher material. These features support the hypothesis that Europa is covered by a crust of ice several kilometers thick that rides on top of a liquid or slushy ocean. The colors in the image are exaggerated but otherwise natural. The smooth terrain would appear slightly bluish and the ridges slightly yellow to orange to the eye. Yellow colors may be the result of sulfur compounds.
		Double Ridge on Europa This single Galileo image shows a double ridge at high resolution. The size of the image is about 14 x 17 kilometers, or 15 meters/pixel. The entire region is covered by smaller double ridges and grooves.
		Europan Ice Pack This simulated color Galileo mosaic of a 70 x 30 kilometer part of the Conamara region of Europa shows what appears to have been a crust covered with double ridges, then shattered into fragments, then refrozen. Colors were added to a black and white mosaic in order to produce this image. No upended iceberg appears to be more than a kilometer or so thick, indicating that the crust may have been that thin when the region shattered. NASA hopes that future missions can chart the actual thickness of the ice, and that later "hydrobots" might travel beneath it to search for life.
		Jupiter's Moon Ganymede from 3.4 Million Kilometers Voyager 1 view of Ganymede, Jupiter's largest moon, from a distance of about 3.4 million kilometers (2.1 million miles). This color image is composed of images taken through three different filters. Note the intricate light and dark markings on the suface, which hint at a complex history. (Voyager 1, P-21186)
		Complex Structures on Ganymede This Galileo image of Ganymede shows two kinds of tectonic features. On either end there is folded, marbled terrain, and in the center a band of parallel folds or fractures. The surface of Ganymede is largely water ice, and these features result from the stretching and folding of this ice. The driver of these motions is possibly a subsurface liquid mantle of water, like the more well-known one speculated for Europa. The entire region is peppered with small craters.
		Impact Craters and Tectonics on Ganymede In this close-up, it is possible to see how several features on Ganymede are related. The lines on the surface can be seen to cross the two craters, indicating that the craters were made first, then fractured by the line-forming process. The fact that there are few craters on Ganymede and that many that are have been altered indicates that the crustal motions of Ganymede are continuing, possibly to the present day.
		Jupiter's Moon Callisto Callisto is the outermost of Jupiter's large moons and the one that appears most similar to our moon. Like the other Jovian moons, it is made of water ice. The dark brown material is probably sulfur compounds originating at Io. When a comet or asteroid hits the surface, the resulting crater is white because it digs up cleaner ice.
		Impact Features on Callisto One of the most dominant features on Callisto is a concentric ring impact feature called Asgard. This Galileo mosaic shows a tiny part of this feature at high resolution. The fuzzy features around the outside of the sharper image are part of a low-resolution context image. The ridge near the bottom is one of the rings caused by the Asgard impact. The white material at right is ejecta from a nearby impact. The feature at the top, called Doh, is the analog of a crater on an icepack: the penetration caused the upwelling or expansion of slushy material which "erupted" onto the surface to form a dome. (Doh is the name of the Ketian shaman said to have created the earth, not the sound Callisto made when hit by the meteor.)