Ganymede (moon)
Ganymede (gan'-É™-meed, ; Greek
Î"ανυμήδης) is
Jupiter's largest
moon, and indeed the
largest moon in the entire
solar system; it is larger in diameter than
Mercury but only about half its mass. Ganymede is much larger than
Pluto. Ganymede is the only planetary satellite (besides the Moon) that can be seen by the naked eye â€" but only with very good eyesight during ideal conditions. It might have first been seen by
Chinese astronomer Gan De in
364 BC. Discovery of the moon is generally credited to
Galileo Galilei who documented its existence in
1610. The name Ganymede was soon after suggested by
Simon Marius, for the cup-bearer of the
Greek gods, beloved of
Zeus (see
Ganymede (mythology)). This name and the names of the otherGalilean satellites fell into disfavor for a considerable time, and were not revived in common use until the mid-
20th century. In much of the earlier astronomical literature, it is simply referred to by its Roman numeral designation as
Jupiter III or as the "third satellite of Jupiter". Ganymede is the only Galilean moon of Jupiter named after a male figure.
Ganymede is composed of
silicate rock and
water ice, with an ice crust floating over a warmer ice
mantle that may contain a layer of liquid water. Indications from the
Galileo orbiter data suggest that Ganymede is differentiated into a three layer structure: a small partially molten
iron or iron/
sulfur core surrounded by a rocky silicate mantle with an icy shell on top. This metallic core suggests a greater degree of heating at some time in Ganymede's past than had previously been proposed. In fact, Ganymede may be similar in its internal structure to
Io.
 |
Interior of Ganymede |
The Ganymedean surface is a mix of two types of terrain: very old, highly cratered dark regions and somewhat younger (but still ancient) lighter regions marked with an extensive array of grooves and ridges. Their origin is clearly of a
tectonic nature, probably formed by the extension, stretching, and faulting of the icy crust. Analogous tectonic features form the ridges and valleys in the
Basin and Range province of the southwestern United States. Features reminiscent of old
lava flows have also been observed. Similar ridge and groove terrain is seen on
Enceladus,
Miranda and
Ariel. The dark regions are similar to the surface of
Callisto.
Extensive
cratering is seen on both types of terrain. The density of cratering indicates an age of 4
billion years for the dark terrain, similar to the highlands of the
Moon, and a somewhat younger age for the bright grooved terrain (but how much younger is uncertain). Craters both overlay and are cross cut by the groove systems indicating that some of the grooves are quite ancient. Relatively young craters with rays of ejecta are also visible. Unlike on the Moon, however, Ganymedean craters are quite flat, lacking the ring mountains and central depressions common to craters on the Moon and Mercury. This is probably due to the relatively weak nature of Ganymede's icy crust which can flow and thereby soften the relief. Ancient craters whose relief has disappeared leaving only a "ghost" of a crater are known as
palimpsests.
The largest feature on Ganymede is a dark plain named
Galileo Regio, as well as a series of concentric grooves, or furrows, that are remnants of an ancient impact crater long since obscured by subsequent geological activity.
In the mid-1980s, a team of Indian and American astronomers working at Indonesia's Lembang Observatory detected a thin atmosphere around Ganymede during an
occultation when Jupiter passed in front of a star. Evidence for a tenuous
oxygen atmosphere on Ganymede, very similar to the one found on
Europa, has been found by the
Hubble Space Telescope. Note that this is not evidence of life: it is thought that the oxygen is produced when water ice on Ganymede's surface is split into
hydrogen and oxygen by radiation and then the hydrogen is lost due to its low atomic mass.
The
Galileo orbiter's first flyby of Ganymede discovered that Ganymede has its own magnetic field, embedded inside Jupiter's huge field. Ganymede is the only moon known to have a
magnetosphere. Ganymede's intrinsic magnetic field is probably generated in a similar fashion to the Earth's: as a result of conducting material moving in the interior, likely originating in its metallic core. Ganymede also has an induced magnetic field component, indicating that the satellite contains a subsurface layer that acts as a conductor. It is thought that this conductive material is a layer of liquid water containing
salt, located at about 150 km depth and sandwiched between layers of different density forms of ice.
* In the short stories "
Not Final" (1941) and "
Victory Unintentional" (1942) by
Isaac Asimov, a conflict arises between humans living on Ganymede and the inhabitants of Jupiter.
*
Robert A. Heinlein's novel
Farmer in the Sky (1950) depicts the
terraforming and
colonization of Ganymede. In Heinlein's novel
Space Cadet (1948), one of the characters is listed as being a third generation colonist on Ganymede.
*
Leigh Brackett's short story
The Dancing Girl of Ganymede (1950) is set on a volcanic, jungle-covered Ganymede.
* Ganymede is referred to in virtually all of
Philip K. Dick's novels from the 50s and 60s, although it seldom receives more than a brief mention. In "
Clans of the Alphane Moon" (1964), we are introduced to Lord Running Clam, a species of intelligent
slime mold from Ganymede.
* In the
Lester Del Rey book "The Runaway Robot" (1965), the main character Paul and his robot live in a colony on Ganymede at the beginning of the story.
* In the
Star Trek episode "By Any Other Name" (1968), Scotty asserts a green beverage was obtained on Ganymede, but he might be mistaken.
* A book
I visited Ganymede by peruvian writer Yosip Ibrahim relates in first person the story of a friend
Pepe that keeps contacts with a civilisation in Ganymede. In this perfect civilisation whose inhabitants communicate via telepathy there are no wars and illness. The book follows the
UFO religion line and plays with the story being actually true.
* The German movie "
Operation Ganymed" (1977) - made for TV - tells the story of five astronauts returning from an expedition to Ganymede. They find a seemingly desolate Earth and are trying to find out what happened while they were in space.
*
The Gentle Giants of Ganymede (1978) by
James P. Hogan ISBN 0345314697. An alien spaceship is found on Ganymede.
* In
Arthur C. Clarke's novel
2061: Odyssey Three (1987), Ganymede is warmed by the new sun Lucifer and contains a large equatorial lake. It is the centre of human colonization of the Jovian system.
* In the 32nd Millennium of the
Warhammer 40,000 (1987) Universe, Ganymede is destroyed during a Warp Core experiment that goes horribly wrong.
* The 1991 science fiction novel
Buddy Holly Is Alive and Well on Ganymede, by
Bradley Denton (ISBN 0688108229 and ISBN 0380718766), begins when television sets throughout the world suddenly begin broadcasting a concert by an apparently living Buddy Holly, who says he is on Ganymede.
* In the
Power Rangers TV series (1993-), Ganymede is the hiding place chosen by
Zordon as the hiding space for a fleet of
Zords known as the Mega Vehicles, which combine to form the Mega Voyager. The
Space Rangers locate these Zords after winning Key Cards from
Darkonda in a card game. (
"Flashes of Darkonda",
"The Rangers' Mega Voyage").
* In the
science fiction TV series
Babylon 5 (1994-1998), the
Shadows bury a ship under the surface of Ganymede, which is dug up during the third season of the show (the
Messages From Earth episode, 1996).
* The majority of events in "
The Ganymede Club" (1995), a science fiction mystery by
Charles Sheffield, take place on Ganymede.
* In the
animated television series The King of Braves GaoGaiGar (1997), many of the 31 Machine Primevals fuse with Jupiter's satellites as their last stand against heroic Gutsy Galaxy Guard. The Primeval to fuse with Ganymede is Lungs Primeval (ZX-17), which creates a "Klein Space" within itself (a pocket dimension bearing spatial geometry similar to that of a
klein bottle) in an attempt to seal GGG away upon their arrival in Jovian orbit.
* Ganymede is portrayed in the
anime series
Cowboy Bebop (1998). It is depicted as an aquatic planet, a
terraformed world that is entirely covered in water. Animal life, most likely created by human intervention, is also depicted, such as the Ganymede searat, a species of rodent-like seal. About 7 million people live on it in floating colonies which are supported on large barge-type foundations. The character Jet Black was a police officer on Ganymede, and presumably was born there. Jet also has a watch that is apparently from Ganymede.
* In the novel
Orphanage (2004) by
Robert Buettner, an alien race uses Ganymede as a staging area for a war against Earth.
* In the DOS game
One Must Fall: 2097, the prize for victory in the tournament is the development right to Ganymede, which is also the home of the Angels, who seek to prevent their home being developed.
* In the PC game
FOM , Ganymede is a space colony which has been terraformed to support humanity.
*
List of craters on Ganymede* The
asteroid 1036 Ganymed
