Overview (The Solar System)
Ganymede, the largest satellite of Jupiter, was discovered by Galileo Galilei with a telescope in 1610. He published the information in Siderius Nuncius (starry messenger) and thereby initiated a dispute with the Church that would eventually lead him to be placed under house arrest for the remainder of his life; it was heresy to say that anything revolved around something other than the Earth. The satellite was named by Simon Marius for one of the lovers of the Roman god Jupiter.
Ganymede is 5,280 kilometers in diameter, and just over 1 million kilometers from Jupiter; it is the seventh of sixteen satellites. It is common for a satellite to present the same face to its planet at all times—a relationship called synchronous—and Ganymede does this, just as Earth’s moon does. The rotation of Ganymede is prograde, that is, in the same direction as that of Jupiter. Ganymede’s orbit is almost circular, meaning that its Eccentricity (the measure of how close to a Circular orbit the satellite travels) is small. A circular orbit has an eccentricity of zero. Ganymede’s angle of inclination is less than a degree, meaning that this moon rotates almost exactly in the plane of Jupiter’s equator.
Ganymede’s albedo, the amount of sunlight reflected, is large. This Reflectivity is caused by ice mixed with carbon-rich soil on the surface of the satellite. When the ice underneath the surface is heated and melts, it...
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Knowledge Gained (The Solar System)
The Jovian system, as Jupiter and its moons are called, has been visited by several space missions. Pioneer 10 (1973), Pioneer 11 (1974), Voyager 1 and Voyager 2 (both in 1979), and New Horizons (2007) flew through the system. They all used gravitational assists to gain speed to travel on toward the outer part of the solar system.
The Pioneer Spacecraft provided the first visual images of the surface of Ganymede, as well as a much better estimate of the size and mass of Ganymede. The Voyager spacecraft improved these images to a Resolution of a Kilometer and provided color by means of six filters. Scientists were able to develop ideas of how the satellite formed and its structure. The Voyager data on craters indicated either that Ganymede’s surface has changed, and thus erased the early craters from meteor hits, or that the surface was not firm enough to retain the early craters.
The Galileo mission arrived in orbit about Jupiter in 1996. The visual camera increased the resolution of the surface to 20 meters. The model of the moon, showing its core, mantle, and shell of ice, was developed after data from Galileo provided Ganymede’s mass, average density, and moment of inertia. The moment of inertia and average density required the data on gravitational fields produced by Galileo, and how the Flight path was perturbed as the craft flew by the satellite. Galileo also provided information of the magnetic fields using...
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Context (The Solar System)
The more astronomers learn about large bodies like Ganymede, the more is revealed about how the Solar system was formed and about Earth and its Moon. Ganymede may be showing the action of plate tectonics. Learning about the Plate tectonics of Ganymede may explain what happened on Earth as the continents tectonically rearranged.
Each space mission has returned valuable information on how to survive in space. Not only are meteorites a danger but gravitational wells, and especially strong magnetic fields, can damage a spacecraft. When humans venture forth, all of those dangers will have to be considered. The number of craters on Ganymede gives scientists some indication of the chance of a meteor hitting the Earth.
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Further Reading (The Solar System)
Asimov, Isaac, and Richard Hantula. Jupiter. Milwaukee, Wis.: Gareth Stevens, 2002. The famous science-fiction author covers the planet and its satellites, the space missions that have studied them, and the comet collisions of 1994. Illustrations, bibliography, index.
Corfield, Richard. Lives of the Planets. New York: Basic Books, 2007. The author takes the reader through the different space missions. Divided by planets, the information gathered by each mission is discussed. Index.
Fischer, Daniel. Mission Jupiter: The Spectacular Journey of the Galileo Spacecraft. New York: Copernicus Books, 2001. The author takes the reader through each step of the journey of this amazing space probe. Illustrations.
Grundy, W. M., et al. “New Horizons Mapping of Europa and Ganymede.” Science 318 (2007): 234. This article is one of the first published after the flyby of Jupiter by the Pluto-bound New Horizons spacecraft. Illustrations, bibliography.
Leutwyler, Kristin. The Moons of Jupiter. New York: W. W. Norton, 2003. Ganymede is covered in one of the main sections of this book. Illustrations, index.
McFadden, Lucy-Ann Adams, Paul Robest Weissman, and T. V. Johnson, eds. Encyclopedia of the Solar System. San Diego: Academic Press, 2007. The editors have collected articles written by many experts in one of the best scholarly surveys of material about the...
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Ganymede (Myths and Legends of the World)
Greek myths describe Ganymede as a handsome boy who was kidnapped by the gods to serve as a cupbearer on Mount . Born in Troyancient city that was the site of the Trojan War; present-day Turkey near the Dardanelles, where his father was king, Ganymede came to the attention of , who was captivated by his appearance. In some stories, it is Zeus disguised as an eagler an eagle sent by Zeusho seizes the boy and carries him up to the home of the gods.
In return for his son, Ganymede's father received a group of immortalable to live forever horses from Zeus. Some versions of the tale say that the gift was a vine made of gold. Later Zeus placed Ganymede in the sky in the constellation Aquarius. Images of Ganymede sometimes show him carrying a cup or accompanied by an eagle.
See also ZEUS.
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