Jupiter's Moons

INTRO: 
      Jupiter has 16 moons, most of which are small and minor, less than fifty 
miles across. It does, however, have four large moons. The four Galilean 
satellites were discovered by Galileo in 1610. Callisto is the furthest with 
a heavily cratered and dark surface. Ganymede, second most distant of the four
and the largest satellite in the solar system, has heavily cratered regions 
surrounded by a grooved terrain. It is also larger than the planet Mercury. 
Europa is a white, highly reflecting body whose smooth surface is entirely 
covered with dark streaks up to 70 km in width and from several hundred to 
several thousand kilometers in length. While Callisto is dark surfaced, Europa 
is light surfaced. Io, the closest to Jupiter of the four, has eight active 
volcanoes that are energized by the tidal effects of Jupiter's enormous mass. 
It is slightly larger than our own moon. The red color of Amalthea, another 
satellite is due to a coat of sulfur particles. Four space probes have 
encountered the Jovian system.

CALLISTO:
      Callisto is the outermost satellite of Jupiter's four largest moons. 
It is about 1,170,000 miles from Jupiter, with an orbital of 16 2/3 days. 
The diameter is 4800 km, almost the size of the planet, Mercury. Its density 
is 1.8 gm/cc. This low density rules out the the possibility that this moon is 
made of rock. It seems to have a rocky core surrounded by ice. Callisto formed 
in a frozen environment far away from the sun, leading us to believe that water
ice may have been a major component of the material that condensed to form this
body. Unlike the other larger moons of Jupiter, Callisto's surface is completely
covered by craters. It has more craters than any other moon in our solar system.
They were formed billions of years ago when meteors crashed in to the moon and 
melted the surface ice. Voyager cameras have revealed a surface that is dark 
but filtered images have shown that the dark regions were more red than the 
lighter ones. The most unique feature of the surface was a large bulls eye 
structure, with a bright center of about 600 km in diameter. This central 
region was surrounded by rings separated by about 50-200 km and extending 
2000 km. Callisto's crust reacts differently to large impacts than Mercury 
or our moon. Just as in all cases, kinetic energy must be deposited 
instantaneously at an impact site, but the post impact recoveries differ.

GANYMEDE:
       Ganymede is the largest satellite in the solar system. It has a diameter
of 5260 km and is larger than Mercury. It revolves around Jupiter at a distance
 of 9.5 planetary radii, with a period of 7.16 days. A large amount of water 
ice is present at the surface. Ganymede has three layers. A small iron or iron 
and sulfur core, a rocky mantle surrounding the core, and an icy shell on top. 
The surface is a mix of dark, rocky soil and white ice. These icy regions are 
covered by long, narrow ridges of ice mingled with dust and rock. Dark grooves 
or valleys lie between the ridges. Ganymede can reflect about 44 percent of 
the light on its surface which indicates that it is covered by dark material. 
It is heavily cratered and has regions with ridges or faults with a structure 
similar to a bulls eye. This region is known as the Galileo Regio. There are 
many trends among the craters. The larger the diameter, the flatter is the 
appearance. Small craters are often bowl like and similar to those of our own 
moon. The other most common terrain of Ganymede is less cratered and more 
reflective. Other features include impact basins, ray craters, etc.

IO: 
        Io is the most volcanic moon in the Solar System. It has many 
different surfaces including volcanic craters, lakes of molten sulfur, 
mountains, and lava flows. Some spots may reach 1,000 degrees Fahrenheit. 
When viewed by the Voyager, there were 9 erupting volcanoes all concentrated 
towards the equator. A detection of water ice or even steam on Io was not 
found. There were spectral lines of double ionized sulfur. Sulfur was abundant 
on the surface and because of this the surface of Io, seems white. It is 
slightly larger than our moon and orbits Jupiter every 1.75 days at a distance 
of 262,000 miles. As Io orbits Jupiter, the planet's gravity stretches Io 
slightly. This heats the moon's inner rock, causing the rock to melt and 
explode in eruptions that shoot gas and sulfur in to the sky. 

EUROPA: 
        Europa is the smallest of the Galilean moons. It is about 1,942 miles 
across and 417,000 miles from Jupiter. It completes one orbital every three 
and a half days. The surface is covered with ice. From a distance, it looks 
like a smooth, white ball. Compared to our moon, Europa is much brighter with 
a 64 percent reflectivity compared to the moon's seven percent. The ground 
based infrared spectra has shown that there is a lot of water ice present on 
the surface. Europa is covered with brown tinted ice. Scientists believe that 
more ice or water may like beneath the icy crust. A detailed inspection has 
shown that there are fewer than twelve circular craters that have been formed 
from meteoric impacts. This information leads to the belief that Europa's 
surface is mobile and can erase all but the most recent impacts. There are 
several types of terrain on the surface. These include plains cut by grooves 
and ridges. The mottled terrains are either brown or gray, The brown tint is 
due to angular structures and vertical ridges. The gray regions show less 
distinction. There are many linear grooves and macula (brown regions). This 
satellite consists of a rock core covered by a crust of ice. Fractures that 
have formed may be the result of tidal stresses.

ADRASTEA: 
      This satellite was discovered in 1979 by the Voyager. It is third in 
distance from the planet, about 128,980 km away. Adrastea's period of 
revolution is 0.298 days and has a 0 degree of inclination as well as an 
eccentricity of 0. Adrastea's radius is 96 km.

AMALTHEA:
       This satellite was discovered in 1892. It is 181,300 km away from 
Jupiter. Amalthea's period of revolution is 0.498 days and has a 0.4 degree 
of inclination. Its eccentricity is 0 as well. Almathea's orbit of Jupiter 
takes about twelve hours. It is an irregular ellipsoidal satellite with a 
cratered surface. It is aligned with Jupiter's shortest axis and the axis of 
rotation is perpendicular to the plane of the orbit or Jupiter's equator. 
Amalthea's diameter is 270 km along the longest axis and 155 km along the 
shortest axis. This moon is the largest among the four inner moons. There 
may be sulfur rich material on Amalthea because it's reflectivity is very 
low and its color is a dark red. 

ANANKE:
       This satellite was discovered in 1951. It is the 14th in distance 
from the planet, about 21,200,000 km away. Ananke's period of revolution is 
631 days and has a 147^2 degree of inclination. Ananke's eccentricity is 0.17. 
It's radius is 3375 km.

CARME:
       This satellite was discovered in 1938. It is 15th in distance from the 
planet, about 22,600,000 km away. Carme's period of revolution is 692 days and 
it has a 163^2 degree of inclination. It's eccentricity is 0.21. Carme's radius 
is 10,648 km. 

ELARA:
       This satellite was discovered in 1905. It is the seventh largest moon 
of Jupiter and the 13th in distance. It is about 11,737,000 km away. Elara's 
period of revolution is 259.65 days and has a 28 degree of inclination. It's 
eccentricity is 0.71. Elara's radius is 64,000 km.

HIMALIA:
      This satellite was discovered in 1904. It is eleventh in distance from 
the planet and about 11,480,000 km away. Himalia's period of revolution is 
250.57 0.298 days and has a 28 degree of inclination. It's eccentricity is 
0.16. Himalia's radius is 270,000 km.

LEDA:
      This satellite was discovered in 1974. It is tenth in distance from 
the planet, about 11,094,000 km away. Leda's period of revolution is 238.72 
days and has a 29 degree of inclination. It's eccentricity is 0.15. Leda's 
radius is 512 km.

LYSITHEA: 
      This satellite was discovered in 1938. It is twelfth in distance from 
the planet and is about 11,720,000 km away. Lysithea's period of revolution is 
259.22 days and has a 29 degree of inclination. It has an eccentricity of 0.11.
Lysithea's radius is 8000 km.

METIS:
      This satellite was discovered in 1979 by the Voyager. It is second in 
distance from the planet and is about 127,960 km away. Metis' period of 
revolution is 0.295 days and has a 0 degree of inclination. Metis' 
eccentricity is 0 as well. It's radius is 20 km.

PASIPHAE:
      This satellite was discovered in 1908. It is sixteenth in distance from 
the planet and about 23,500,000 km away. Pasiphae's period of revolution is 
735 days and has a 147^2 degree of inclination. Pasiphae's eccentricity is 
0.38. It's radius is 42,875 km.

SINOPE:
      This satellite was discovered in 1914. It is seventeenth in distance 
from the planet and is about 23,700,000 km away. Sinope's period of revolution 
is 758 days and has a 153^2 degree of inclination. It has an eccentricity of 
0.28. Sinope's radius is 8000 km.

THEBE:
      This satellite was discovered in 1979 by the Voyager. It is fifth in 
distance from the planet and about 221,900 km away. Thebe's period of 
revolution is 0.675 days and has a 0.8 degree of inclination. Thebe's 
eccentricity is 0.01. It's radius is 50 km.