This is a true-color image of Io taken by the Galileo probe. Credit: NASA.
Io is a rocky-object that is irradiated by the Sun.
Io is also in a planetary-type orbit around Jupiter.
In the image, "[t]he smallest features that can be discerned are 2.5 kilometers in size. There are rugged mountains several kilometers high, layered materials forming plateaus, and many irregular depressions called volcanic calderas. Several of the dark, flow-like features correspond to hot spots, and may be active lava flows. There are no landforms resembling impact craters, as the volcanism covers the surface with new deposits much more rapidly than the flux of comets and asteroids can create large impact craters. The picture is centered on the side of Io that always faces away from Jupiter; north is to the top."
This image of Callisto from NASA's Galileo spacecraft, taken in May 2001, is the only complete global color image of Callisto obtained by Galileo. Credit: NASA/JPL/DLR(German Aerospace Center).
Above is a complete global color image of Callisto.
This region of Callisto shows the transition from the inner part of an enormous impact basin, Asgard, to the outer surrounding plains. Credit: NASA/JPL.
"This fascinating region [in the image at the right] of Jupiter's icy moon, Callisto, shows the transition from the inner part of an enormous impact basin, Asgard, to the outer "surrounding plains." Small, bright, fine textured, closely spaced bumps appear throughout the inner part of the basin (top of image) and create a more fine textured appearance than that seen on many of the other inter-crater plains on Callisto. At low resolution, these icy bumps make Asgard's center brighter than the surrounding terrain. What caused the bumps to form is still unknown, but they are associated clearly with the impact that formed Asgard."
"The ridge that cuts diagonally across the lower left corner is one of many giant concentric rings that extend for hundreds of kilometers outside Asgard's center. Exterior to the ring (lower left corner), Callisto's surface changes significantly. Still peppered with craters, the number of icy bumps decreases while their average size increases. The fine texture is not as visible in the middle of the image. One explanation is that material from raised features (such as the ridge) may slide down slope and cover small scale features. Such images of Callisto help us understand the dynamics of giant impacts into icy surfaces, and how the large structures change with time."
"North is to the top of the picture. The image, centered at 27.1 degrees north latitude and 142.3 degrees west longitude, covers an area approximately 80 kilometers (50 miles) by 90 kilometers (55 miles). The resolution is about 90 meters (295 feet) per picture element. The image was taken on September 17th, 1997 at a range of 9200 kilometers (5700 miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft during its tenth orbit of Jupiter."
This image shows two views of the trailing hemisphere of Jupiter's ice-covered satellite, Europa. The left view shows the approximate natural color appearance of Europa. Credit: NASA/Deutsche Forschungsanstalt für Luft- und Raumfahrt e.V., Berlin, Germany.
The image is a composite of two views of Europa. The left view shows the approximate natural color appearance of Europa. The view on the right is a false-color composite version combining violet, green and infrared images to enhance color differences in the predominantly water-ice crust of Europa. Dark brown areas represent rocky material derived from the interior, implanted by impact, or from a combination of interior and exterior sources. Bright plains in the polar areas (top and bottom) are shown in tones of blue to distinguish possibly coarse-grained ice (dark blue) from fine-grained ice (light blue). Long, dark lines are fractures in the crust, some of which are more than 3,000 kilometers (1,850 miles) long. The bright feature containing a central dark spot in the lower third of the image is a young impact crater some 50 kilometers (31 miles) in diameter. This crater has been provisionally named "Pwyll" for the Celtic god of the underworld. This image was taken on September 7, 1996, at a range of 677,000 kilometers (417,900 miles) by the solid state imaging television camera onboard the Galileo spacecraft during its second orbit around Jupiter.
A true color image of Ganymede is acquired by the Galileo spacecraft on June 26, 1996. Credit: NASA/JPL.
This is global pictoral map of Ganymede. Credit: National Oceanic and Atmospheric Administration/USGS.
"If Ganymede rotated around the Sun rather than around Jupiter, it would be classified as a planet."
The Galilean Moons is a "name given to Jupiter's four largest moons, Io, Europa, Callisto & Ganymede. They were discovered independently by Galileo Galilei and Simon Marius."
"Ganymede has a very distinct surface with bright and dark regions. The surface includes mountains, valleys, craters and lava flows. The darker regions are more heavily littered with craters implying that those regions are older. The largest dark region is named Galileo Regio and is almost 2000 miles [3200 km] in diameter. The lighter regions display extensive series of troughs and ridges, thought to be a result of tectonic movement."
"A notable attribute of the craters on Ganymede is that they are not very deep and don’t have mountains around the edges of them as can normally be seen around craters on other moons and planets. The reason for this is that the crust of Ganymede is relatively soft and over a geological time frame has flattened out the extreme elevation changes."
These are greyscale Galileo images of Amalthea. Credit: .
Amalthea is in a close orbit around Jupiter and is within the outer edge of the Amalthea Gossamer Ring, which is formed from dust ejected from its surface. From its surface, Jupiter would appear 46.5 degrees in diameter. Amalthea is the largest of the inner satellites of Jupiter. Irregularly shaped and reddish in color, it is thought to consist of porous water ice with unknown amounts of other materials. Its surface features include large craters and ridges.
Amalthea was photographed in 1979 by the Voyager 1 and 2 spacecraft, and later, in more detail, by the Galileo orbiter in the 1990s.
↑ 2.02.1Thomas, P. C.; Burns, J. A.; Rossier, L.; Simonelli, D.; Veverka, J.; Chapman, C. R.; Klaasen, K.; Johnson, T. V. et al. (September 1998). "The Small Inner Satellites of Jupiter". Icarus135 (1): 360–371. doi:10.1006/icar.1998.5976.
Himalia is seen by spacecraft Cassini. Credit: .
Mean orbit radius of Himalia around Jupiter is 11,460,000 km
"Unfortunately the numeration of Jupiter's satellites is now in precisely the same confusion as that of Saturn's system was before the numbers were abandoned and names substituted. A similar course would seem to be advisable here; the designation V for the inner satellite [Amalthea] was tolerated for a time, as it was considered to be in a class by itself; but it has now got companions, so that this subterfuge disappears. The substitution of names for numerals is certainly more poetic."
The moon was sometimes called Hestia, after the Hestia the Greek goddess, from 1955 to 1975.
At a distance of about 11.5 million km from Jupiter, Himalia takes about 251 Earth days to complete one orbit. It is the largest member of the Himalia group, the moons orbiting between 11.4 and 13 million kilometres from Jupiter at an inclination of about 27.5°. The orbital elements are as of January 2000.