The following notices contains data which were discovered about the Jovian environment by the Galileo mission. Some data from additional and later studies may have been added, chronologically to the texts as they mostly are pointed to
->More About Jupiter by Cassini on its Route to Saturn (December 2000)
During a six-month period, included a gravity-assisted flyby there, the Cassini mission to Saturn flew by Jupiter by December 2000, allowing for more science about the gas giant. Convective lightning storms were seen evolve over time as heights and composition of these storms and the many clouds, hazes and other types of storms that blanket Jupiter were better caracterized. A dark oval around 60 degrees North latitude was spoted, a giant storm like Jupiter's Great Red Spot as quite transient, developing a
bright inner core, rotating and thinning over six months. Such a oval may have been associated with Jupiter's powerful auroras. Scientists also saw that ordered flow of the eastward and westward jet streams in low latitudes gives way to a more disordered flow at high latitudes, or a intense equatorial
eastward jet (310 mph, or 500 km/h) high in the stratosphere, about 60 miles (100 kilometers) above the visible clouds. A cosmic sonic boom also is occuring when supersonic solar wind is slowed and deflected around the magnetosphere surrounding Jupiter as that protective magnetic bubble has been observed contracting as a region of higher solar wind pressure blew on it. Organic molecule acetylene exist
at the north and south poles of Jupiter as such a enhanced emission results both from the warmer
temperatures in the auroral hot spots, and probably also from an enhanced abundance in these regions. A invisible wave as seen by the Cassini mission on its way to Saturn, in 2000, is shaking up one of Jupiter's jet streams, an interaction that also takes place in Earth's atmosphere and influences the weather. At the difference of the meandering jets at Earth, those at the giant planet are straight and narrow but they display some wandering comportment too and take a aspect of chevrons when they hit a Rossby wave, or a gravity inertia wave which are resonances in the atmosphere. The presence of the transient large storm, and the Great Red Spot in the southern hemisphere of Jupiter likely explains that jet streams behave differently either side of the equator
 | That true color mosaic of Jupiter was constructed from images taken by the Cassini mission in December 2000, during its closest approach to the giant planet at a distance of approximately 6.2 million miles. picture courtesy NASA/JPL/Space Science Institute |
->More About Jupiter and the Moons by New Horizons on its Route to Pluto (Feb. 28, 2007)
On its route to Pluto, the NASA New Horizons mission used Jupiter like a gravity assisted-flyby booster and it put the occasion to profit by using its science tools about the gas giant and its moons. Detailed views and speed measurement of those 'waves' which run the width of the planet and indicate violent storms under were taken, as clumps of debris -maybe indicating a recent impact- have been seen inside the tenuous rings of Jupiter. Metis and Adrastea there have been seen sheperding the materials as no new tiny moon was revealed. Io, as far as it is concerned, has been observed with more than 20 geological changes since the Galileo mission and its plumes were observed, as tons of materials from Io's volcanoes have been detected down Jupiter's magnetic tail's charged particles flow, moving there grouped into large, dense blobs. Ammonia clouds have been observed welling up from the lower atmosphere and, for the first time outside the Earth, polar lightnings have been observed, hinting to that the heat at Jupiter is upwelling at any latitudes, the poles included. Details of Jupiter's high-altitude clouds emerge in the methane absorption band picture above, as taken Feb. 28, 2007, by some 1.4 million miles (2.3 million km) from the gas giant. Images taken through this filter preferentially pick out clouds that are relatively high because sunlight at the wavelengths transmitted by the filter is completely absorbed by the methane gas that permeates Jupiter's atmosphere before it can reach the lower clouds. A south pole cap is seen which likely is a haze of small particles created by the precipitation of charged particles into the polar regions during auroral activity as cirrus-like clouds are shredded by winds reaching speeds of up to 400 miles per hour just above the equator
 | Methane absorption band picture of Jupiter as taken Feb. 28, 2007 by the New Horizons mission. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute |
->More About Jupiter By the Juno Mission
With it suite of instruments allowing deep into Jupiter and to its magnetosphere, Juno is a NASA mission to Jupiter which launched Aug. 5, 2011 and which has settled into a polar orbit around the gas giant since July 4, 2016. Engineers downgraded from a 14 to a 53-day orbit for cause of a technical glitch. A color camera, the Junocam serves to bring public interest into Jupiter with crowdpicture editing. Jupiter’s gases are no well mixed down to hundreds of miles in depth like expected as the interior is patchy. Levels of ammonia are low also except a ammonia-rich plume rising from the depths at the equator, which could hint to that ammonia might be distributed like water vapour on Earth, with higher humidity along the equator and lower levels at higher latitudes. The powerful magnetic field of Jupiter was found more powerful still, and patchy too (with a variety of places whence the field's lines originate, and variable as it is stronger near the equator). That uneven distribution suggests that the field might be generated by dynamo action closer to the surface, above the layer of metallic hydrogen. Jupiter 's core is large, at 7–25 times the mass of the Earth, and diffuse, reaching out to as much as half of the planet's radius. Cloud bands extend as much as 250 miles deep albeit displaying new twists and turns, the equatorial belt excepted which stays the same at depth. Jupiter's poles are of a bluer hue than the rest of the planet, and covered in Earth-sized swirling storms that are densely clustered and rubbing together. Ghostly-sounding radio emissions emanating from above the planet have been known about since the 1950s but had never been analyzed from such a close vantage point as Juno also could observe the southern aurora from a better vantage point than from Earth. At the difference of what exists at Saturn, Jupiter doesn't feature any hexagon at its north pole. By late 2017, the Juno mission also showed showed that Jupiter's Great Red Spot has roots penetrate about 200 miles (300 kilometers) into the planet's atmosphere. A new radiation zone was detected surrounding Jupiter at very close just above the atmosphere, and located near the equator as the zone includes energetic hydrogen, oxygen and sulfur ions moving at almost light speed. The particles are believed to be derived from energetic neutral atoms (fast-moving ions with no electric charge) created in the gas around the Jupiter moons Io and Europa. The neutral atoms then become ions as their electrons are stripped away by interaction with the upper atmosphere of Jupiter. Juno also found signatures of a high-energy heavy ion population within the inner edges of Jupiter's relativistic electron radiation belt -- a region dominated by electrons moving close to the speed of light
The east-west flows are accounting for 'bands,' also known as jet-streams as the weather layer, generally, is extending much deeper than previously expected at 1,900 miles (3,000 kilometers), or about one percent of Jupiter’s mass, in the form of nested cylinders. Below this layer the flows decay, possibly slowed by Jupiter's strong magnetic field. Winds last long at Jupiter as there is also a North-South asymmetry. Beneath the weather layer, the planet rotates nearly as a rigid body. Juno has also revealed that a central cyclone is found at Jupiter's both poles, surrounded by eight cyclones North and five South (with diameters 2,500-2,900 miles (4,000-4,600 kilometer) North, and 3,500-4,300 miles (5,600-7,000 kilometers) South). The main question about such cyclones is why they don't merge
By about 1,900 miles (3,000 kilometers) of depth, hydrogen becomes conductive enough to be dragged into a near-uniform rotation by Jupiter magnetic field. Jupiter's dynamo source region, on a other hand, revealed unexpected irregularities, regions of surprising magnetic field intensity, and that Jupiter’s magnetic field is more complex in the northern hemisphere than in the southern. About halfway between the equator and the north pole lies a area where the magnetic field is intense and positive. It is flanked by areas that are less intense and negative. In the southern hemisphere, however, the magnetic field is consistently negative, becoming more and more intense from the equator to the pole. The researchers are still figuring out why they would see these differences in a rotating planet that’s generally thought of as more-or-less fluid
Jupiter
Four Galilean Satellites
Io
Europa
Ganymede
Callisto
Rings and Minor Moons
JupiterJupiter is characterized by alternate equatorial cloud belts. Such belts are produced by jet streams alternating in direction. Ovals of clouds are circulating along the belts. Some have a very long existence like the most famous "Great Red Spot" which has been seen existing since 300 years. Tall convective white cloud standing about 15 miles (25 kilometers) higher than surrounding clouds exist at Jupiter with a base very deep in the atmosphere, about 30 miles (50 km) and composed of water which is sole to withstand the heavier pressure there. Such storms might erupt each 10 days and lasting a few days, with lightning in there, with a size 620 miles (1000 km) across. The atmosphere of Jupiter generally is mostly transparent at a wavelength of 756 nanometer as a strong absorption occurs at 889 and 727 nm. The atmospheric probe released into Jovian atmosphere did not return any picture but a series of weather data. That Galileo's probe in 1995 found high winds and turbulence in Jupiter's atmosphere, as expected water seemed to be absent (which might be due to the probe dropped into a dry area of the atmosphere)
 | 10-50° northern hemisphere mosaic. This view provides an usual view of Jupiter with its alternated cloud belts and white ovals, bright and dark spots or turbulent chaotic systems. Northernmost weather feature is 2,175 km (3,500 km) North-South. picture courtesy California Institute of Technology |
 | Great Red Spot is seen just on the limb (right) as eddies are seen left. False color image (bottom) is showing how clouds are organized into various layers (light blue clouds are high and thin, reddish clouds are deep as white clouds are high and thick). picture courtesy California Institute of Technology |
 | Great Red Spot is seen here full frame in violet and near-infrared. Winds are blowing counterclockwise at about 250 mph (400 km/h). The size of the Great Red Spot is 8,000 miles (13,000 km) North-South, that is more than Earth's diameter. The Great Red Spot is more than two Earth diameters East-West. picture courtesy JPL |
 | This a three dimensional visualization of a 21,100 by 6,800 miles (34,000 km by 11,000 km) Jupiter's equatorial region. It is reducing Jupiter's true cloud structure to two layers, one of haze, one of tropospheric clouds. Light bluish clouds are high and thin, reddish clouds are low as white clouds are high and thick. Dark blue large spot in the center is a hole in the lower cloud layer where air is rising from deep atmosphere as surrounding dry air is converging and sinking there. picture courtesy California Institute of Technology |
 | These views due to Cassini en route to Saturn are showing Jupiter magnetosphere (left) and radiation belts close to Jupiter (right). Jupiter is shown left as a black circle along with a cross-section of Io torus. Jupiter magnestosphere is tilted relative to the planet's axis. picture based on pictures courtesy Johns Hopkins University Applied Physics Laboratory (left part) and JPL (right part) |
Four Galilean SatellitesFour Galilean satellites, Io, Europa, Ganymede, Callisto, are the four major satellites of Jupiter. Their were named from Galileo Galilei who first saw them using the first telescope ever. Io, Europa, Ganymede, and Callisto are respectively 2,264 (3,643 km; similar to Earth's Moon), 1,940 (3,122 km), 3,270 (5,262 km), and 2,996 miles (4,821 km) wide. All Gallilean satellites, Callisto excepted, have metallic cores (iron, nickle) surrounded by rock shells. At Europa and at Ganymede, such mantles are in turn surrounded by liquid water or water ice as the mantle at Io it going all the way to the surface. Callisto interior is thought to be an uniform mix of ice and rock. Recent data are showing that, inferred from gravity anomalies seen during Galileo flybys, rocky lumps exist at Ganymede. They might be situated anywhere between near the surface and along an underlying ocean bottom. Densities of the four large Galilean satellites, as found by the Pioneer 10 mission, decrease with distance from the planet, a phenomenon reflected in the innermost planets of the solar system
 | Four Galilean satellites are shown here by increasing distance from Jupiter (from left to right): Io, Europa, Ganymede, Callisto. All four satellites are to scale. picture courtesy DLR (German Aerospace Center) |
 | Gallilean satellites interior. Clockwise starting top left: Io, Europe, Callisto, Ganymede. Moons and layers at scale. picture courtesy JPL |
IoIo endures gravitational stresses as it the nearest Galilean moon to Jupiter, featuring a 1600° Celsius internal temperature as a 300-foot high bulging is caused at the surface by the passage of a gravitational tide. That is caused by that the orbits of Io, Europe and Ganymede are in a resonance 4-2-1 tending to slightly ovalize the one of Io. This is yielding internal heat and volcanism. Io is the most volcanically active object in the solar system. The volcanoes are caused by tidal heating endured at Io, which are the result of gravitational forces from Jupiter and other moons. These forces result in geological activity, most notably volcanoes that emit umbrella-like plumes of sulfur dioxide gas that can extend up to 300 miles (480 kilometers) above Io and produce extensive basaltic lava fields that can flow for hundreds of miles (kilometers). Io is mostly volcanism-generated plains and mountains with a surface younger than a million years as Io is continually resurfaced. Relief features may change on scales of months only. Io, for example, saw three massive volcanic eruptions within a two-week period by August 2013, the largest ever observed on the moon. As astronomers typically expect one huge outburst every one or two years as that might be more as astronomers usually look for those every year only. Lava likely blast out of fissures perhaps several miles long as the magma of Io likely looks like that of the primitive Earth, with higher temperatures. Io is devoided of craters. Io’s thin atmosphere, which consists primarily of sulfur dioxide (SO2) gas emitted from volcanoes, collapses as the SO2 freezes onto the surface as ice like frost during Io's eclipses, then is restored when the ice warms and sublimes. Io's atmosphere thus is in a 'a constant state of collapse and repair.' During a eclipse, the temperatures at Io drops from -235 degrees Fahrenheit in sunlight to -270 degrees Fahrenheit as a eclipse occurs two hours of every Io day, which is 1.7 Earth days. Io possesses also a ionosphere. On another hand the magnetic field of Jupiter which is sweeping at Io is stripping material and is ionizing it, forming along the moon's orbit a doughnut-shaped cloud (a "torus") of radiation, sodium gas, and sulfur ions. It is these ions which are inflating Jupiter magnetosphere twice the size it should have. Jupiter's active moon Io creates glowing footprints near Jupiter's north and south poles. Data analysis made in May 2011 has revealed a layer of molten or partially molten magma at Io, which likely explains why the moon is the most volcanic object known in the solar system. Such a layer is found beneath the 20 to 30-mile (30 to 50-km) thick crust of Io, as it itself features a width of more than 30 miles (50 km). It may be considered the 'asthenosphere' of Io, a mobile zone made of semi-solid magma able to soften and flow after subjected to high temperature and pressure. At Earth, the asthenosphere is responsible for plate tectonics. The heat for the volcanic activity of Io comes from squeezing and stretching by Jupiter's gravity and Io thus produces about 100 times more lava each year than all the volcanoes on Earth. While Earth's volcanoes occur in localized hotspots like the 'Ring of Fire' around the Pacific Ocean, Io's volcanoes are distributed all over its surface, which provides for a window in time showing that different styles of volcanic activity likely occurred, at different times, in the solar system. The discovery was made possible because of the disturbance Io brings to Jupiter magnetosphere's field lines. As Jupiter rotates, its magnetic lines drape and vary around Io as the moon's own inner magnetic field remain shielded an retains a vertical orientation. That observable disturbance eventually led astronomers to think that a magma ocean with a high electrical conductivity, and deflecting Jupiter field, was extant. They also have been able to accurately define the composition of such a layer, which is composed of so-called 'ultramafic' rocks, a class of igneous rocks rich in iron and magnesium silicates formed from the cooling of the original magma. And especially of a rock similar to Earth's lherzolite as found in Spitzbergen, Norway. The molten magma layer of Io probably endures temperatures in excess of 2,200 degrees F (1,200 degrees C). Io is caught in a tug-of-war between Jupiter's massive gravity and the smaller but precisely timed pulls from two neighboring moons that orbit further from Jupiter, Europa and Ganymede. Io orbits faster than these other moons, completing two orbits every time Europa finishes one, and four orbits for each one Ganymede makes. This regular timing means that Io feels the strongest gravitational pull from its neighboring moons in the same orbital location, which distorts Io's orbit into an oval shape. This in turn causes Io to flex as it moves around Jupiter. Should tidal heating occurred primarily within the deep mantle, surface heat flow concentrates primarily at the poles, as with heating primarily within the asthenosphere near the equator. Prevailing view is that most of the heating occurs within a relatively shallow layer under the crust, called the asthenosphere. The asthenosphere is where rock behaves like putty, slowly deforming under heat and pressure. Astronomers generally found a systematic eastward offset between observed and predicted volcano locations. That allowed to state by 2015 that Io features a internal ocean made of a magma as Europa also participates into tidal heating with a regular timing of two orbits of Io to one of Europa. Io's volcanism is so extensive that it gets completely resurfaced about once every million years
 | This tremendous view of Io is showing the moon's very active surface. picture courtesy University of Arizona / LPL |
 | Zal Patera region at Io is shown in a combination of black and white and color images. Various relief features are seen: a plateau, 6,600 ft (2,000 m) high (top left), a caldera (right of the plateau), a mountain (bottom right of the previous), a peak (bottom right), 14,000 ft (4,200 m) high. Surface at Io is mostly sulfur and deposits of frozen sulfur dioxide. picture courtesy University of Arizona |
 | Here is one of the famed volcanic plumes seen at Io. This one is rising about 60 miles high (100 km) at Masubi region. picture courtesy University of Arizona / LPL |
EuropaContrasting with Io, Europa is an icy world. Europa's ice crust is fractured by tidal flexing from Jupiter, Io, and Ganymede as such a process may be accompanied with possible ice-rock volcanoes and geysers. Flexing also is heating Europa's interior hence that local or a global subterranean ocean(s) might be found beneath the surface. The scarcity of impact craters suggests that the surface of Europa is very young. Like Mars, Europa is a good match in the solar system where life is possible. As life at Mars might be of the desert or hydrothermal kind, life at Europa might be of the polar type. Reddish material seen in quantities at Europa might be a non-ice contaminant like salts which is brought up from the underlying ocean. Scientists are sure now that the icy crust of Europa is made of blocks which at a time broke apart and then shifted into new positions against each other. The red scars criss-crossing Europa are actually cracks and ridges marking weak lines within the moon’s ice crust, emphasised and exacerbated by the swelling and falling of tides due to Jupiter’s gravitational pull. Bands and groove lanes found on Europa and Ganymede might result from the moon's ice shell deformed by gravitational interactions with Jupiter as the material found there is a fossil ocean material dating back to when it was uplifted to the surface. The regions of mottled red are chaotic terrain, parts of the moon’s surface with disrupted icy material that has been broken and shifted around. A subsurface ocean might have helped, as a magnetic field at the moon is another hint to a subterranean ocean. A tenuous atmosphere exist at Europe as it is very thin. Such that thin, hot gas around the moon does not show evidence of plume activity as the plasma further existing around Europa's orbit is a hot rather than a cold one suggesting that Europa is not outputting large amounts of gas including water. Traces of water vapour above the surface of Europa were confirmed by November 2019. Io thus remains the major contributor, in terms of particles, in the Jovian system
Plate tectonics on Europa, the first spotted on a world other than Earth, has been evidenced in 2014 as it works based upon the ice the moon is made of. Many parts of Europa’s surface show evidence of extension, where wide bands miles wide formed as the surface ripped apart and fresh icy material from the underlying shell moved into the newly created gap, a process akin to seafloor spreading on Earth. Some terrain also moves under some other as that yields ice volcanoes on the overriding plate, possibly formed through melting and absorption of the slab as it dove below the surface, and a lack of mountains at the subduction zone, implying material was pushed into the interior rather than crumpled up. Europa's ice shell, may be up to 20 miles (30 kilometers) thick. Plate tectonics at Europa might also move material from the surface into the subterranean ocean. Dark lanes seen on the surface likely are subsumption band which got worn out. Plate tectonics might be allowed by that a cold, denser outer ice shell is setting atop a warmer, convecting one below. The dark material coating some geological features of Europa is likely sea salt from subsurface ocean, discolored by exposure to radiation and suggesting the ocean is interacting with its rocky seafloor. Europa indeed is bathed in radiation created by Jupiter's powerful magnetic field. Electrons and ions slam into the moon's surface with the intensity of a particle accelerator
A ocean at Europa might consists of a subsurface salty ocean with also partially melted pockets, or lakes throughout the moon's outer shell, maintained by Jupiter' tidal heating. The yellow color visible on portions of the surface of Europa is actually sodium chloride, or table salt, which reinforces the idea that, if the material derived from the Moon subsurface oean, the latter might chemically resemble Earth's oceans more than previously thought. Studies by 2010 have shown that underlying layers in Europa may be hiding more than a presumed ocean and likely the scene of some unexpectedly fast chemistry between water and sulfur dioxide at extremely cold temperatures. Although these molecules react easily as liquids they react as ices with surprising speed and high yield at temperatures hundreds of degrees below freezing. Because the reaction occurs without the aid of radiation, it could take place throughout Europa's thick coating of ice. Should no volcanism occur, which is paramount to a habitable environment in that ocean the thinking goes, the large flux of oxidants from the surface would make the ocean too acidic, and toxic for life as, should the rock be cold, easier to fracture, that allows for a huge amount of hydrogen to be produced by 'serpentinization,' producing hydrogen from rock cracks, that would balance the oxidants in a ratio comparable to that in Earth's oceans. The moon's temperature hovers around 86 to 130 Kelvin. In this extreme cold, most chemical reactions require an infusion of energy from radiation or light. On Europa, the energy comes from particles from Jupiter's radiation belts. Because most of those particles penetrate just fractions of an inch into the surface, models of Europa's chemistry typically stop there. Once you get below Europa's surface, it's cold and solid, and you normally don't expect things to happen very fast under those conditions. Sulfur at Europa originates in the volcanoes of Jupiter's moon Io, then becomes ionized and is transported to Europa, where it gets embedded in the ice. Additional sulfur might come from the ocean that's thought to lie beneath Europa's surface. In experiments that simulated the conditions on Europa, water vapor and sulfur dioxide gas were sprayed onto mirrors in a high-vacuum, freezed chamber as the gases immediately condensed as ice. The reaction converted one-quarter to nearly one-third of the sulfur dioxide positive and negative ions which further could react with other molecules. This could lead to some intriguing chemistry, especially because bisulfite (HSO3–), a type of sulfur ion, and some other products of this reaction are refractory—stable enough to stick around for a while Even with frozen carbon dioxide, aka dry ice, which is commonly found on icy bodies, the reaction continued, which means it could be significant on Europa as well as Ganymede and Callisto, two more of Jupiter's moons, and other places where both water and sulfur dioxide are present. Such a chemistry could occur in layers of ice 33 or 330 feet (10 or 100 m) thick as water and sulfur dioxide thus are reacting as solids. Data in November 2011 likely demonstrate that albeit several miles thick, the ice crust at Europa however might have provided for interactions with the underlying global oceans. Life indeed need some energy, like in the form of heat, or radiations like a trigger. Chaos features at Europa, as inferred from studies about Arctic and Antarctica on Earth, might have formed by mechanisms that involve significant exchange between the icy shell and underlying lakes. This provides a mechanism or model for transferring nutrients and energy between the surface and the underground, increasing the potential for life there. By 2016, high altitude, 125-mile (200-kilometer) water vapor plumes might exist at Europa, hinting to the possibility that missions to Europa may be able to sample Europa’s ocean without having to drill through miles of ice. Europa plumes could flare up intermittently in the same region on the moon's surface, matching a unusually warm anomaly that contains features that appear to be cracks in the icy crust. Radiation from Jupiter can destroy molecules reaching at Europa's surface from the ocean below, possibly destroying any biosignatures, or biochemical signs. The radiation doses vary by location with the harshest radiation concentrated in zones around the equator, and the radiation lessens closer to the poles. Radiation, on the other hand, dips into Europe' soil from 4 to 8 inches in the highest-radiation zones –- down to less than 0.4 inches deep in regions of Europa at middle -- and high-latitudes, toward the moon's poles
 | Various icy features at Europa southern hemisphere surface. The two dark spots South are Thera Macula and Thrace Macula. Such features are thought to be scars of ancient large impacts. picture courtesy JPL |
 | Northern hemisphere Europa icy crust. An old, almost purely water ice, blue, surface is scratched by ridges and spots. An astronaut orbiting Europa would see the surface somewhat brighter but with less intense colors. picture courtesy DLR (German Aerospace Center), University of Arizona |
 | Blue-white terrains indicate relatively pure water ice, whereas the reddish areas contain water ice mixed with hydrated salts, potentially magnesium sulfate or sulfuric acid. The reddish material is associated with the broad band in the center of the image, as well as some of the narrower bands, ridges, and disrupted chaos-type features. It is possible that these surface features may have communicated with a global subsurface ocean layer during or after their formation. The image area measures approximately 101 by 103 miles (163 km by 167 km). picture courtesy NASA/JPL-Caltech/SETI Institute |
 | Modern image processing techniques were used by 2020 to create new views of Europa surface, preparing for the arrival of the Europa Clipper spacecraft from left to right: chaos terrain at Chaos Transition, Chaos Near Agenor Linea, Crisscrossing Bands. picture courtesy NASA |
 | A 2014 reprocessed, true color view using modern image processing techniques, made from a mosaic of images taken by Galileo. That image is the largest one with the most sharp details (caution when downloading! the picture is 1.7 Mo). picture courtesy NASA/JPL-Caltech/SETI Institute |
 | That picture is the highest resolution view ever obtained of Europa's Jupiter-facing side. It was obtained on Nov. 25, 1999 by the Galileo spacecraft. Linear features in the center of this mosaic and toward the poles may have formed in response to tides as some extend for over 900 miles (1,500km). Darker regions near the equator may be vast areas of chaotic terrain. Bright white spots are ejecta blankets of young impact craters. picture courtesy NASA/JPL/University of Arizona |
 | That is the most detailed view of the surface of Europa obtained by NASA's Galileo mission. With the Sun relatively high in the sky, most of the brightness variations visible here are due to color differences in the surface material rather than shadows. Bright ridge tops are paired with darker valleys, perhaps due to a process in which small temperature variations allow bright frost to accumulate in slightly colder, higher-elevation locations. picture courtesy NASA/JPL-Caltech |
GanymedeGanymede is being impressively resurfaced by tectonics. Ganymede had already been well observed by Voyager. Galileo performed detailed observations only. Ganymede is a world with a part rock, part ice, crust. Its marbled surface is shaped by tectonics as impact craters are seen too. Ganymede is the largest moon in the solar system, larger than Mercury and ¾ the size of Mars. Ganymede was found to have a magnetosphere of its own as embedded into Jupiter's one
  | Ancient terrain at Ganymede is dark. Young terrain is bright. Bright spots and strikes are impact craters and their ejecta. Picture right is from Voyager 1. pictures courtesy JPL |
 | Two varieties of terrain are seen here in more details. A dark, heavily cratered, ancient terrain, left and a bright, younger, grooved, terrain, right. The brighter terrain was likely formed by flooding of the surface with water coming from faults or even cryo-volcanos that have taken place over billions of years as even tectonic processes also took part. Deep groves may exist at the limit between both terrains. picture courtesy Brown University |
CallistoCallisto is the most heavily cratered body seen in the solar system. This means that the outermost Galilean satellite was geologically inactive since the earliest origins of the solar system. Callisto's surface is thought to be 4 billion years old! A difference however is seen between a darker and a brighter terrain. This might be a difference between an ice-poor, highly eroded, terrain, and ice only. The moon is made up of equal parts of rock and ice. Callisto is the third largest satellite in the solar system. It's almost the size of Mercury but only about a third of the mass. Albeit featuring a subterranen ocean, Callisto interior is cold mostly as erosion on Callisto craterized terrain was caused by ground ice evaporating away. Callisto orbits relatively far away from Jupiter compared to these other satellites as this isolation means that Callisto does not experience any significant tidal forces from Jupiter like Io, Europa and Ganymede
  | These general views of Callisto are showing the heavily cratered, very ancient, surface of Callisto. Picture right is by Voyager 2 and uses an ultraviolet image for the blue component. picture courtesy NASA/JPL/ DLR (German Aerospace Center) (left) and JPL (right) |
 | Multi-ring impact structure Asgard is one of the largest impact structures at Callisto. It is about 1,050 (1,700 km) miles wide. Smaller and more recent impacts excavated brighter icy material. picture courtesy University of Arizona / LPL |
Rings and Minor MoonsIt's the Voyager missions which first saw Jupiter's faint ring. Galileo mission brought a better understanding of it. Rings are due to dust particles which are blasted off by micrometeorites from four small moons lying inside Io's orbit. Metis and Adrastea -small objects of 12 and 25 miles (20 and 40 km) wide are producing the main closer ring as the larger Amalthea and Thebe -117 and 60 miles (189 and 100 km), are yielding the two exterior inner and outer Gossamer rings. A halo is found between the main ring and Jupiter. It is due to particles being magnetically pushed away from the ring's plane. Gossamer rings' thickness is due to the orbital inclination of Amalthea and Thebe's orbits. The 'main ring' might be about 600 miles (1000 km) wide, as it's likely corralled into that width by the Amalthea and Metis. More recent views taken by NASA's mission New Horizons on its way to Pluto, in February 2007, hint to that it might that an until now unseen moon might further gauge its path in the middle of that part of the ring
Amalthea, from data acquired during the November 5th, 2002 flyby and studied in 2005, was found a pile of icy and rocky rubble, with a density far inferior to the one of water ice. This is challenging what was thought about Jupiter's moons formation as the formation of the Jovian system was considered the equivalent of that of the solar system, that is the heat of Jupiter had just blown away the ice and gas from the inner regions. This might hint to Amalthea to have formed later than the other moons, or further and then migrated inwards, or to have formed isolated from the Jovian system and then captured
 | This view is showing Jupiter's rings and the four inner moons found at the origin of the ring system. picture courtesy Cornell University |
 | Four Jupiter's inner moons (from left to right: Thebe, Amalthea, Adrastea, Metis). These small satellites are irregular in shape due to a long history of highly energetic impacts from meteoroids and fragments of asteroids and comets. picture courtesy Cornell University |
