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*Callisto was discovered by Galileo in 1610.

*It is around 4.5 billion years, about the same as Jupiter itself.

*Callisto is one of the most heavily cratered moons in our Solar System.

*There is no atmosphere on Callisto.

*There have been many expeditions on Callisto.

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BBC News. BBC. Web. 22 Feb. 2016.
"Callisto, Moon of Jupiter - The Solar System on Sea and Sky." Callisto, Moon of Jupiter - The Solar System on Sea and Sky. Web. 22 Feb. 2016.
"Jupiter Moon Callisto." Jupiter Moon Callisto. Web. 22 Feb. 2016.
"Callisto - Overview | Planets - NASA Solar System Exploration." NASA Solar System Exploration. Web. 22 Feb. 2016.
"Callisto: Facts about Jupiter's Dead Moon." Space.com. Web. 22 Feb. 2016.

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Callisto, one of Jupiter’s 67 moons, was discovered January 7, 1610 by Galileo Galilei. This moon is approximately four and a half billion years old. I takes about seven Earth days for Callisto to orbit Jupiter. When Galileo discovered this moon, he named it Jupiter IV. There are many characteristics of Callisto, like it’s craters, almost as striking as the planet Jupiter itself. Zero signs have been found that it’s exterior has changed in the four billion years it has existed. This proof has caused particular interest in Callisto. Many other characteristics of Callisto include multi-ring structures and Catenae. Catenae are lines of craters. One other characteristic of Callisto are it’s icy peaks that scatter it’s surface.

The moon Callisto was originally anticipated to be inactive. But on the contrary, recent statistics show the opposite of that. This data showed that Callisto might actually have a salty ocean underneath it’s crust. This ocean is possibly greater than 10 kilometers (6 miles) thick. This particular ocean has a bizarre inside that doesn’t vary as fiercely as other moons. This interior is made up of ice and rock. As the depth of Callisto increases, so does the percentage of rock becomes higher as well. Meteorites have produced holes in the moon. These holes have caused water to stretch across the exterior of Callisto. This water makes bright rings and rays around it’s craters. There is no known atmosphere on Callisto.

There have been many explorations on Callisto. The first exploration was Pioneer 10. That was in 1973. Another expedition on Callisto was Pioneer 11 in 1974.    It wasn’t until Voyager 1 and Voyager 2 that followed those that we were allowed to have beautiful pictures of Callisto. These photos show us Callisto’s very many craters. Callisto is one of the most cratered moons in the Solar System. It’s craters are probably Callisto’s most known and prominent feature. Also, Callisto is so large, that it is almost to the equivalent size of Mercury. It is thought that Callisto could eventually harbor life. Fortunately, this could happen around 2040.

When Callisto was discovered by Galileo in 1610, he also discovered Io, Europa, and Ganymede. He named these four moons “Medicean Stars” after the rich Medici Family. Astronomers call these I, II, III, and IV according to their distance from Jupiter. It wasn’t until the 17th Century that astronomers started calling these moons by their proper names. Obviously, Callisto is one of the most important astronomical discoveries made before. It is about 1,882,70 km (1,169,856 miles) from Jupiter itself. It is also 4,800 kilometers in diameter. This makes it the third largest satellite in the Solar System.  With it’s crater-filled exterior, it makes Callisto one of the most original moons in outer space. Even though there hasn’t been any recorded changes on Callisto for four and a half billion years, it’s spectacular sight makes it a favorite topic for scientists and people everywhere.