# Ganymede

Taking a new step...is what people fear most. - Dostoyevski

Jupiter III

## Table of Contents

- Ganymede (This page)
  - Ganymede Statistics
  - Animations of Ganymede
  - Views of Ganymede
- !!! New Images of Ganymede Taken by Galileo
- Hubble Finds Ozone on Jupiter's Moon Ganymede
- The Discovery of the Galilean Satellites

Ganymede [GAN-ee-meed] is the largest moon of Jupiter and is the largest in our solar system with a diameter of 5,262 km (3,280 miles). If Ganymede orbited the Sun instead of Jupiter it could be classified as a planet. Like Callisto, Ganymede is most likely composed of a rocky core with a water/ice mantle and a crust of rock and ice. Its low density of 1.94 gm/cm3, indicates that the core takes up about 50% of the satellite's diameter. Ganymede's mantle is most likely composed of ice and silicates, and its crust is probably a thick layer of water ice.

Ganymede has no known atmosphere, but recently the Hubble Space Telescope detected ozone at its surface. The amount of ozone is small as compared to Earth. It is produced as charged particles trapped in Jupiter's magnetic field rain down onto the surface of Ganymede. As the charged particles penetrate the icy surface, particles of water are disrupted leading to ozone production. This chemical process hints that Ganymede probably has a thin tenuous oxygen atmosphere like that detected on Europa.

Ganymede has had a complex geological histroy. It has mountains, valleys, craters and lava flows. Ganymede is mottled by both light and dark regions. It is heavily cratered especially in the dark regions implying ancient origin. The bright regions show a different kind of terrain - one which is grooved with ridges and troughs. These features form complex patterns and have a vertical relief of a few hundred meters and run for thousands of kilometers. The grooved features were apparently formed more recently than the dark cratered area perhaps by tension from global tectonic processes. The real reason is unknown; however, local crust spreading does appear to have taken place causing the crust to shear and separate.

## Ganymede Statistics

    Discovered by ................ Simon Marius & Galileo Galilei
    Date of discovery ...................................... 1610

    Mass (kg) .......................................... 1.48e+23
    Mass (Earth = 1) ................................. 2.4766e-02
    Equatorial radius (km) ................................ 2,631
    Equatorial radius (Earth = 1) .................... 4.1251e-01
    Mean density (gm/cm^3) ................................. 1.94

    Mean distance from Jupiter (km) ................... 1,070,000
    Rotational period (days) ........................... 7.154553
    Orbital period (days) .............................. 7.154553
    Mean orbital velocity (km/sec) ........................ 10.88

    Orbital eccentricity .................................. 0.002
    Orbital inclination ................................... 0.195°

    Escape velocity (km/sec) ............................... 2.74

    Visual geometric albedo ................................ 0.42
    Magnitude (Vo) ......................................... 4.61

## Animations of Ganymede

- Flight over Ganymede from Voyager data - AVI, 3.3M. (Courtesy NASA/JPL)
- Voyager/Galileo Morph Animation of Ganymede - Quicktime, 846K. (Courtesy NASA/JPL)
- Computer Simulation of the Galileo Flyby of Ganymede - 640x480 MPEG, 1.6M; Quicktime, 4.2M; 320x200 MPEG, 887K; Quicktime, 2.8M. (Courtesy NASA/JPL)
- Another Computer Simulation of the Galileo Flyby of Ganymede - 640x480 MPEG, 1.1M; Quicktime, 2.0M; 320x200 MPEG, 701K; Quicktime, 2.2M. (Courtesy NASA/JPL)
- Overhead View of the Galileo Flyby of Ganymede - 640x480 MPEG, 892K; Quicktime, 2.0M; 320x200 MPEG, 759K; Quicktime, 2.2M. (Courtesy NASA/JPL)

## Views of Ganymede

Ganymede (GIF, 187K)
This shows an entire hemisphere of Ganymede. The prominent dark region, called Galileo Regio, is about 3,200 km in diameter. The bright spots are relative recent impact craters. Part of the Galileo Regio may be covered with a bright frost. (Credit: Calvin J. Hamilton)

Model of Ganymede (GIF, 106K)
This is an illustration Ganymede's interior. Its low density indicates that its core takes up about 50% of the satellites radius. The mantle is probably composed of silicates, water or ice, and the crust is composed of ice less than 75 kilometers in depth. (Courtesy NASA/JPL)

Southern Galileo Regio (GIF, 400K)
This image of southern Galileo Regio shows impact craters in various stages of degradation. Almost all of the craters appear flat. The two prominent light colored craters are almost completely erased by the flow in the icy crust. (Credit: Calvin J. Hamilton)

Impact Crater (GIF, 434K; GIF, 2M)
This mosaic of high resolution images on Ganymede shows a relative fresh impact basin surrounded by ejecta. (Credit: Calvin J. Hamilton)

Craters, Light and Dark Bands (GIF, 412K)
This image of Ganymede was taken by Voyager 1, 246,000 kilometers (158,000 miles) from the planet. The center of the picture is at 19° south latitude and 356° longitude, and the height of the frame represents a distance of about 1000 kilometers (600 miles) on the surface. The smallest features seen on this picture are about 2.5 kilometers (1.5 miles) across. The surface displays numerous impact craters many of which have extensive bright ray systems. The craters lacking ray systems are probably older than those showing rays. Bright bands traverse the surface in various directions and these bright bands contain an intricate system of alternating linear bright and dark lines which may represent deformation of the crusted ice layer. These lineations are particularly evident near the top of the picture. A bright band trending in a north-south direction in the lower left-hand portion of the picture is offset along a bright line. This offset is probably due to faulting. Two light circular areas in the right upper center of the picture may be the scars of ancient impact craters which have had their topographic expansion erased by flowage of the crystal icy material. (Image Copyright Calvin J. Hamilton)

Crescent Image of Ganymede (GIF, 87K)
This beautiful crescent image of Ganymede was taken by Voyager 1 on March 6, 1979. (Copyright Calvin J. Hamilton)

Temperature Map of Ganymede (JPEG, 29K)
This map shows the temperatures for most of the surface of Ganymede made from data taken by the Photopolarimeter/Radiometer (PPR) instrument on June 26, 1996 as Galileo approached the sunlit side of the moon. The color bar shows the range of temperatures of this data, with the dark red being the coldest and white being the warmest. This is similar to the temperature forecast maps that you see on the evening news or in some newspapers. The difference between this map and one of Earth is that PPR measures the temperature of the surface (the ground), instead of air temperature. Ganymede is much colder than Earth, with these daytime temperatures ranging across the surface from 90 to 160 Kelvin (or -297 to -171 degrees Fahrenheit). Jupiter and its moons receive less than 1/30th the amount of sunlight that the Earth does, and Ganymede has essentially no atmosphere to trap heat. Ganymede's day is just over 7 Earth days long, the same time it takes to orbit Jupiter once. (Courtesy NASA/JPL)

Jupiter Europa Callisto

##### Author: Calvin J. Hamilton.