 |
||
| 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: GANYMEDE: |
||
 |
|
 |
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 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.
