Callisto Facts

Callisto Facts

Jupiter’s moon Callisto is the most heavily cratered object in the solar system. It has the oldest landscape and is referred to as the ‘dead moon’.


It is believed that it’s been a long dead world, with hardly any activity on its surface. Let’s explore some facts about Callisto.

Callisto Overview

Age: Callisto is about 4.5 billion years old, around the same age as Jupiter.

Distance from Jupiter: It is the outermost of the Galilean moons. Because of its orbiting distance from Jupiter, about 1,168,000 miles (1,879,713km), it takes about seven Earth days to make one complete orbit of the planet. It also has less tidal influences than the other Galilean moons because it orbits beyond Jupiter’s main radiation belt.

Size: It is 3,000 miles (4,800 km) in diameter and is similar in size to Mercury. It is the third largest moon in the entire solar system. It has the lowest density of the four Galilean moons.

Temperature: The mean surface temperature of Callisto is -218°F (-103°C). 

Who Discovered Callisto?

  • Callisto was discovered by Galileo Galilei on January 7, 1610.
  • It is the fourth of Jupiter’s moons to be discovered by Galileo. 

Galileo Callisto

How did Callisto get its Name?

  • Galileo called this moon Jupiter IV.
  • In the mid 1800’s the numerical naming of the moons was no longer, and a new name was created.
  • The moon was named after the daughter of the King of Arcadia, Lycaon, who was a companion of Artemis, the chaste hunting goddess. Like all of the Greek mythological figures used to name the Jupiter moons, Callisto was seduced by Zeus and became pregnant.
  • To protect Callisto and their son from his jealous wife, Hera, Zeus transformed them into bears and positioned them in the sky where he could watch over them.

 Exploration of Callisto

  • Several spacecraft have flown by Jupiter and its moons.
  • Pioneer 10 arrived first in 1973.
  • This was followed by Pioneer 11 in 1974.
  • Voyager 1 and Voyager 2 returned unbelievable photos during their fly-bys.
  • The Galileo spacecraft passed as low as 162 miles (261 km) over the surfaces of the Galilean moons. That sure is low.


 Features of Callisto

  • The feature that is most prominent on Callisto is its craters. It has the most craters out of any object in the solar system.

Callisto craters

  • Scientists also estimate that it has the oldest surface of any object in the solar system. There are no signs that its landscape has changed in 4 billion years, which has sparked a great scientific interest in the planet.
  • Without the impact of plate tectonics or volcanoes to change the surface, it is believed that any changes in the surface have come as the results of being hit by objects.
  • Distinguishing features of Callisto’s surface include multi-ring structures, impact craters of varying shapes, and lines of craters. Icy peaks also dot the moon’s surface.

Callisto multi-ringed impact basin

  • Another feature of Callisto is its surface colouring. It is the darkest of all of the Galilean moons.
  • Castillo consists of about half water ice and half rocky material, which has magnesium and iron-bearing hydrated silicates, carbon dioxide, sulphur dioxide, and quite possibly ammonia and some other organic compounds.
  • Could it sustain life? Well, scientists believe that it possible could as it has an ocean.
  • It has extremely low radiation levels too, which makes it perfect for future exploration.

Callisto’s Atmosphere

Callisto’s thin atmosphere is composed of carbon dioxide and probably some oxygen. Callisto is thought to have formed as a result of slow accumulation from the disk of gas and dust that surrounded Jupiter after it was formed.

Even though Callisto is considered a dead moon, there is still the possibility that life could exist on this planet. What do you think?

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