Callisto Facts

Callisto Facts
Callisto is the eighth moon of Jupiter and is the most distant to its parent planet. It is Jupiter's second largest moon and the second largest of the planet's known satellites. It is also the third largest moon in the Solar System and nearly the size of Mercury. It orbits just outside of Jupiter's radiation belt. It was discovered on January 7, 1610 by Galileo Galilei, along with three other large Jovian moons which are Ganymede, lo and Europa. Callisto was named after a nymph who was one of Zeus' many lovers. His wife Hera changed her into a bear, then Zeus transformed her into a star and placed her in the sky as the constellation Ursa Major, which is also referred to as the Great Bear. There is also a constellation named Little Bear which was the son of Zeus and Callisto. All of Jupiter's moons are named by Zeus after Greek mythological figures.
Interesting Callisto Facts:
WIth Callisto being similar in size to Mercury, one would think it would be considered a planet, however it orbits the planet Jupiter and not the Sun.
Callisto's surface is the most heavily cratered and one of the oldest landscapes in our Solar System that dates back four billion years, just after the Solar System was formed.
There are no large mountains or volcanoes. The impact craters and multi-ring structures, along with scarps, deposits and fractures, are the only large features that can be found on the surface. The diameters of the impact craters can range from 0.1 kilometers to over 100 kilometers.
There are two featured impact craters to be found on Callisto. The largest impact basin is Valhalla with a diameter of 600 kilometers and the second is Asgard which measures about 1600 kilometers in diameter.
The surface contains water ice, carbon dioxide ice, rock particles and silicate dust, and hydrocarbon compounds. It has an interior ocean likely made of water mixed with ammonia or salts.
Like Europa and Ganymede, a possible subsurface ocean might be composed of salt water where it is speculated that there could be life.
Callisto is 628,300,000 kilometers from Earth, however it appears much brighter in the sky than our Moon when viewed through a telescope, even with our Moon having a distance of just 384,400 kilometers. This is due to the Sun's reflection off the surface of Callisto's thick layer of ice.
One orbit of Jupiter takes Callisto 16.7 days and during that time it will have travelled more than seven million miles. The moon travels at an orbital speed of around 18,400 miles per hour (29,530 kilometers per hour).
Callisto is over a million miles from Jupiter. The average distance between them is 1,169,856 miles (1,882,700 kilometers).
The moon's surface has been studied and explored by the Pioneer, Voyager, Galileo, Cassini and New Horizon missions. NASA reported that a manned mission to Callisto may be possible in the 2040's.
Callisto is not considered to be geologically active, but with the likely presence of an ocean beneath the surface leaves open the possibility that it could harbor life. With its low levels of radiation, it has been considered the most suitable place for a human base for future exploration of the Jovian system.

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