Callisto Moon Facts

Of Jupiter’s 67 moons, Callisto is its eighth and second largest moon. Callisto is close to the size of the planet Mercury, making it the third largest moon in our solar system.

Callisto Moon Profile

Discovered By:Galileo Galilei January 7, 1610
Diameter:4,820.6 km
Mass:1.08 x 10^23 kg (1.5 Moons)
Orbit Distance:1,882,700 km
Orbit Period:16.69 days
Surface Temperature:-139 °C

Who discovered Callisto

Callisto was discovered in 1610 by Italian scientist Galileo Galilei and, along with the other three moons around Jupiter that he discovered: Io, Europa, and Ganymede, they are grouped under the name of Galilean moons.

Like many of the planets and celestial bodies, Callisto is named after a mythological Greek creature.

She was a nymph that fell in love with the Greek god Zeus. As the story goes, Zeus’ wife, Hera, became jealous and turned Callisto into a bear and it was then that Zeus changed Callisto into a star and put her in the Ursa Major constellation.

We know this constellation as the Great Bear, and we can see it in our night sky.

What do we know about Callisto

Although Callisto is about 99% of Mercury’s diameter its mass is only one third of that of Mercury.

This means that Callisto is less dense. Callisto might be a larger size but it is considered to be a moon because it orbits Jupiter.

The only bodies that can be considered planets are those that orbit the sun. Callisto doesn’t have any atmosphere or tectonic action to protect its surface.

This means that any asteroids, comets, dust or dirt that hits the moon show the damage.

Is they any sign of life?

Callisto’s surface is thought to be one of the oldest in our solar system and it is the most heavily-cratered in our solar system. Due to the fact that scientists can’t see any activity on Callisto, it’s thought to be a dead world.

Callisto is made up of around 40% ice and 60% rock and iron. Studies have shown that Callisto also has traces of silicates, carbon dioxide, water ice and even possible compounds that are organic below its surface.

What did the space mission Galileo find?

It was the Galileo space mission that revealed the possibility of Callisto having possible liquid water under the surface.

Other moons of Jupiter are affected by each other’s gravitational pull, causing tidal heating. Callisto doesn’t seem to be affected in that way.

Tidal heating allows for the release of the heat through the moons crust and Callisto doesn’t show any signs of melting ice on its surface.

Callisto is affected less by Jupiter because it is millions of miles away.

Facts about Callisto

  • Callisto’s surface is made of an incredibly thick ice layer and this makes it very reflective. When we look at Callisto through a telescope it appears brighter than our own moon.
  • It takes 16.7 Earth days for Callisto to orbit its parent planet, Jupiter.
  • In one Callisto full orbit, Jupiter will have traveled over 7 million miles.
  • Callisto is moving at a rate of 18,400 mph/29,530 kmh
  • Being tidally locked, one face of Callisto will always face Jupiter while the other side will always point away.
  • Callisto has huge craters, the largest crater is named Valhalla and is almost 4,000 km across.
  • Scientists have noted that Callisto has a thin atmosphere and they think it is made of carbon dioxide and molecular oxygen.
  • Callisto is believed to have been created from the dust and gas that once surrounded Jupiter.
  • Most scientists agree that due to the lack of geological activity, the possibility of life on Callisto is small, however, there may be life below Callisto’s surface.
  • Future explorers may consider Callisto as a potential for a human base due to lower radiation levels.
  • Europa is another of Jupiter’s moons and scientists are looking to Europa as a potential base due to lower radiation levels than even Callisto.
  • In the future, NASA plans a space mission called JUICE (Jupiter Icy Moon Explorer) that will have a main focus of exploring 3 of Jupiter’s icy moons, including Callisto.


  • Who discovered Callisto?
    Gallileo Galilea
  • What position does Callisto have in Jupiter’s 67 moons?
  • What planet in our solar system is similar in size to Callisto?
  • Does Callisto have an atmosphere?
    yes, a thin one
  • Who is Callisto named after?
    a Greek mythological nymph that was in love with Zeus
  • What is the surface of Callisto made of?
    thick ice