Callisto spacepedia

Planet of Origin



Galileo Galilei

Date of Discovery

January 7, 1610

Surface Color

Brownish gray


Porous ice water

Alternate Name(s)

Jupiter IV


Minus: Mean: Max: 80.5K 134.11K 165.5K

Callisto, also known as Jupiter IV, is a satellite belonging to the outer planet, Jupiter. It is one of the Galilean moons, a group of the largest moons in the Solar System that were discovered by Galileo Galilei. Callisto was founded by Galileo Galilei on January 7, 1610, the same day as Ganymede, also a Galilean moon, and the largest moon in the Solar System, was discovered.


Though many theories surround the creation of Callisto, the most widespread and believed theory is that Callisto was normal D-type asteroid orbiting the Sun in the Asteroid belt. As it was in this belt, it suffered many collisions, which is also the theory of how Callisto contains such as massive core. Once the asteroids collided together, it created heat, which caused the asteroids to fuse together. Once it became massive enough, more collisions pushed Callisto into deep space, where it was grasped into Jupiter's orbit.


Callisto is composed of water ice, carbon dioxide, and other compounds. About one hundred kilometers under the surface of Callisto, there is an ocean, much like any other Galilean moons and other moons of Jupiter.


The surface of Callisto is extremely cratered. There are no signs of volcanism, or any other forms of volcanic activity, or any other signs of surface disrupt. It shows that there have been severe cases of impacts, meaning this moon has an extremely thin atmosphere. The surface is covered with white streaks and valleys caused by these collisions. As these collisions began to pile up, the surface began to become more fragile. And due to the thin atmosphere, Callisto surface became very vunerable to these asteroid impacts. It is believed that in the next million years, Callisto's surface will begin to wear away, causing Callisto to implode on its self.


The atmosphere of Callisto is completely surrounded with an extremely thin layer of carbon dioxide and possibly molecular oxygen. There is also an intense layer called the ionosphere, which is an atmosphere full of active ions that reflect radio waves

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