Ganymede

Ganymede is the seventh and largest satellites of Jupiter's. Ganymede is the third of the Galilean moons. orbit: 1,070,000 km from Jupiter and It's diameter: 5262 km, and its mass is : 1.48e23 kg. Ganymede was a Trojan boy of great beauty whom Zeus carried away to be cup bearer to the gods. Discovered by Galileo and Marius in 1610. Ganymede is the largest satellite in the solar system. It is larger in diameter than Mercury but only about half its mass. Ganymede is much larger than Pluto.

Physical characteristics

Ganymede And Jupiter

The solar system's largest moon, Ganymede, is captured here alongside the planet Jupiter in a color picture taken by NASA's Cassini spacecraft on Dec. 3, 2000. Ganymede is larger than the planets Mercury and Pluto and Saturn's largest moon, Titan. Both Ganymede and Titan have greater surface area than the entire Eurasian continent on our planet. Cassini was 26.5 million kilometers (16.5 million miles) from Ganymede when this image was taken. The smallest visible features are about 160 kilometers (about 100 miles) across.

The bright area near the south (bottom) of Ganymede is Osiris, a large, relatively new crater surrounded by bright icy material ejected by the impact, which created it. Elsewhere, Ganymede displays dark terrains that NASA's Voyager and Galileo spacecraft have shown to be old and heavily cratered. The brighter terrains are younger and laced by grooves. Various kinds of grooved terrains have been seen on many icy moons in the solar system. These are believed to be the surface expressions of warm, pristine, water-rich materials that moved to the surface and froze.

Ganymede has proven to be a fascinating world, the only moon known to have a magnetosphere, or magnetic environment, produced by a convecting metal core. The interaction of Ganymede's and Jupiter's magnetospheres may produce dazzling variations in the auroral glows in Ganymede's tenuous atmosphere of oxygen.

In this global view of Ganymede's trailing side, the colors are enhanced to emphasize color differences. The enhancement reveals frosty polar caps in addition to the two predominant terrains on Ganymede, bright, grooved terrain and older, dark furrowed areas. Many craters with diameters up to several dozen kilometers are visible. The violet hues at the poles may be the result of small particles of frost which would scatter more light at shorter wavelengths (the violet end of the spectrum). Ganymede's magnetic field, which was detected by the magnetometer on NASA's Galileo spacecraft in 1996, may be partly responsible for the appearance of the polar terrain. Compared to Earth's polar caps, Ganymede's polar terrain is relatively vast. The frost on Ganymede reaches latitudes as low as 40 degrees on average and 25 degrees at some locations. For comparison with Earth, Miami, Florida lies at 26 degrees north latitude, and Berlin, Germany is located at 52 degrees north.

Atmosphere Found On Ganymede

Though ozone may be diminishing on Earth, it is being manufactured one-half billion miles away, on Jupiter's largest satellite, Ganymede. NASA's Hubbe Space Telescope found ozone's spectral "fingerprint" during observations of Ganymede made by Keith Noll and colleagues at the Space Telescope Science Institute in Baltimore, Maryland. These Hubble Faint Object Spectrograph results were presented at the American Astronomical Society's 27th Annual Meeting of the Division of Planetary Sciences in Kona, Hawaii.

The amount of ozone detected on Ganymede is small by earthly standards. The total is only a tiny fraction (between 1-10 percent) of the amount of ozone destroyed each winter in Antarctica's notorious "ozone hole" (a location on Earth where ozone levels seasonally drop to extremely low levels.)

Unlike ozone production in Earth's atmosphere, Ganymede's ozone is produced by charged particles trapped in Jupiter's powerful magnetic field (much like the Earth's Van Allen radiation belts). Jupiter's 9-hour, 59-minute rotation sweeps these particles along at tremendous speed, where they overtake the slower moving Ganymede and "rain" down onto the surface. The trailing hemisphere of Ganymede bears the brunt of this particle "sandblasting" (just as our Moon keeps the same face tilted toward Earth, Ganymede keeps the same face turned toward Jupiter, and so has a "leading" and "trailing" hemisphere as it orbits the giant planet).

The charged particles penetrate the ice surface where they disrupt water molecules. Simulations of this unusual environment in laboratory experiments, done by Hubble team member Robert Johnson (University of Virginia), suggest ozone is a possible product when energetic ions known to be present in Jupiter's magnetosphere impact water ice. However, the exact steps leading to ozone production are not yet fully understood, according to Noll.

Though no atmosphere has yet been detected on Ganymede, "the evidence for all this oxygen chemistry going on in the surface ice is a pretty strong hint that Ganymede will also turn out to have a tenuous oxygen atmosphere," said Noll. Earlier this year, Hubble detected a thin oxygen atmosphere on the Jovian moon, Europa.

This observation could only be done using a telescope located in space, because Earth's own atmospheric ozone absorbs the ultraviolet signature of ozone on Ganymede's surface. Ozone's presence was first hinted at during observations with the International Ultraviolet Explorer satellite (IUE), made by Arthur L. Lane of the Jet Propulsion Laboratory and a co-investigator on the HST team. Hubble's greater sensitivity was required to make a definite and unambiguous detection.

Ozone, a relatively unstable molecule made up of three atoms of oxygen, is found in Earth's atmosphere. Most ozone is concentrated in a layer some 16 miles (25 km) above the Earth's surface. This ozone layer is crucial to life on Earth, because it acts as a protective shield from the Sun's harmful ultraviolet radiation which can cause skin cancer, cataracts, and other health problems. Closer to Earth's surface, however, ozone produced from man-made pollutants is harmful, causing damage to lung tissue and plants.

Jupiter's largest moon (3,280 miles or 5,262 km in diameter; 1.5 times the size of the Earth's Moon), Ganymede's surface is composed of rock and ice beneath which lies a water/ice mantle and rocky core, according to models.

Orbital Characteristics - Ganymede