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 history. 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 bySimon Marius & Galileo Galilei
Date of discovery1610
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 eccentricity0.002
Orbital inclination (degrees)0.195
Escape velocity (km/sec)2.74
Visual geometric albedo0.42
Magnitude (Vo)4.61
http://www.solarviews.com/eng/ganymede.htm
Titan
Titan is the fifteenth of Saturn’s known satellites and the largest:
orbit: 1,221,830 km from Saturn
diameter: 5150 km
mass: 1.35e23 kg
In Greek mythology the Titans were a family of giants, the children of Uranus and Gaia, who sought to rule the heavens but were overthrown and supplanted by the family of Zeus.
Discovered by Christiaan Huygens in 1655.
It was long thought that Titan was the largest satellite in the solar system but recent observations have shown that Titan’s atmosphere is so thick that its solid surface is slightly smaller than Ganymede’s. Titan is nevertheless larger in diameter than Mercury and larger and more massive than Pluto.
Surface view
One of the principal objectives of the Voyager 1 mission was the study of Titan. Voyager 1 came within 4000 km of the surface. We learned more in the few minutes of that fly-by than in the previous 300 years. Then in late 2004, the Cassini orbiter began a series of close encounters with Titan, taking data with many instruments. And in January 2005, the Huygens probe actually landed on the surface of Titan and sent back images from the surface.
Titan is similar in bulk composition to Ganymede, Callisto, Triton and (probably) Pluto, ie about half water ice and half rocky material. It is probably differentiated into several layers with a 3400 km rocky center surrounded by several layers composed of different crystal forms of ice. its interior may still be hot. Though similar in composition to Rhea and the rest of Saturn’s moons, it is denser because it is so large that its gravity slightly compresses its interior.
http://www.solarviews.com/eng/titan.htm