Ganymede Facts

Ganymede Facts
The largest moon of Jupiter and in the largest moon in the Solar System is Ganymede. It is larger than Mercury and Pluto, and only slightly smaller than Mars. If Ganymede orbited the sun, it would be classified as a planet. It is 2% larger than Saturn's Titan (second-largest moon of the Solar System) and the ninth-largest object in the Solar System with a diameter of about 3,300 miles (5,268 km). Ganymede is about 4.5 billion years old which is the same age as Jupiter. The moon is the third Galilean satellite and the seventh moon from Jupiter, orbiting at about 665,000 miles (1.070 kilometers). It takes Ganymede roughly about seven Earth-days to orbit Jupiter at a speed of 39,165 km/hr. Ganymede is tidally locked to Jupiter and one side is always facing the planet.
Interesting Ganymede Facts:
Ganymede was discovered by Galileo Galilei on January 7, 1610. It was named for the mythical Greek son of a King who was carried to the sky by Zeus posing as an eagle. Ganymede became the cupbearer of the Olympian gods.
It is the only moon known to have a magnetosphere. That implies there is something inside helping to generate strong magnetic field. Like Europa, Ganymede is thought to have a subsurface ocean, overlying a liquid iron and nickel core. That core is what helps generate the magnetic field. A spherical shell of mostly ice surrounds the rock shell and the core. The ice shell appears to be very thick, maybe 497 miles (800 km) thick. Though it is mostly ice, the ice shell may have rock mixed in.
Ganymede was likely formed in place around the young Jupiter in the early Solar System. It was probably formed by an accretion in Jupiter's subnebula, a disk of gas and dust surrounding Jupiter after its formation.
The daytime temperatures on the surface of Ganymede range from minus 171 degrees Fahrenheit (minus 113 degrees Celsius) to minus 297 degrees Fahrenheit (minus 183 degrees Celsius).
40% of Ganymede's surface is covered with highly cratered dark regions that are believed to be from heavy impact by comets and asteroids that date back to around 4 billion years ago.
It was confirmed by Hubble Space Telescope observations that Ganymede has a thin atmosphere that appears to contain oxygen. The oxygen is likely freed as water ice on the surface is broken apart into oxygen and hydrogen by solar radiation. The atmosphere is far too thin to support life as we know it.
Ganymede orbits Jupiter at a distance of about 665,000 miles (1,070,400 kilometers). It is third among the Galilean satellites and the orbit period is every seven days and three hours.
Several spacecraft orbiting or completed flybys of Jupiter have explored Ganymede. The first mission to explore Ganymede up close was the Pioneer 10. Voyager 1 and Voyager 2 passed by in 1979 and discovered Ganymede was larger than Saturn's moon Titan which was thought to have been bigger. In 1996, the Galileo spacecraft completed a close flyby and discovered the magnetic field, while the discovery of the ocean was announced in 2001.
New Horizons visited in 2007 and sent back images and made topography and composition maps of the moon. So far, spacecraft have only orbited Ganymede and several missions to explore the moon in greater detail have been planned with proposals to land on its surface.

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