13 Callisto Moon Facts | Exciting Facts about Callisto

Callisto makes up one of the four Galilean moons of Jupiter, along with the massive Ganymede, fiery Io and smooth Europa. But what makes Callisto unique and sets it apart from the others? Well, lets look at some facts about Callisto to learn exactly what this moon is about.

Left to Right: Ganymede, Callisto, Io and Europa

Callisto Moon Facts

  1. Callisto has a radius of 1498 miles (2,410.3km), as similar size to the dwarf planet, Pluto.
  2. Callisto is not only Jupiter’s second largest moon, but it’s also the third largest moon altogether. Only Ganymede and Saturn’s moon Titan are bigger.
  3. Like other large moons, Callisto does have a very thin atmosphere. This is primarily made up of carbon dioxide.
  4. Callisto takes it’s name from a nymph in Greek mythology, one of Zeus’s many lovers.
  5. Callisto has long been known as a “dead” planet, due to it’s ancient surface.
  6. It has the most craters of any moon. There are 141 craters, 10 more than Ganymede, the next most cratered moon.
  7. The largest of these craters is called Heimdall, which has a 210km diameter!
  8. The average temperature on the surface of Callisto is approximately -220°c.
  9. Callisto orbits Jupiter at more than a million miles distance. This means that it doesn’t suffer from tidal heating, which affects other, closer moons.
  10. It takes Callisto just under 17 (16.7) days to complete one full rotation of Jupiter.
  11. To complete this, it moves at a pace of 18,400mph (29,530 kilometers per hour).
  12. It’s like that like the other Galilean moons, Callisto formed 4.5 billion years ago with Jupiter.
  13. Thanks to the spacecraft Galileo, we think that there might be an ocean beneath Callisto’s surface.

Common Questions about Callisto

What is Callisto named after?

Callisto is named after one of Zeus’s lovers in Greek mythology. Actually, in some myths she was an unwilling participant in sex with Zeus, which is the darker side of ancient mythology which is lesser mentioned. Supposedly, Zeus’s wife Hera found out about this, and turned her into a bear. She was later cast into the stars, with the bear being part of the Ursa Major constellation.

Is there oxygen on Callisto?

We know that Callisto’s atmosphere is primarily made up of carbon dioxide, but could there be some oxygen in there too? Well according to astronomers, research shows that there could be oxygen in the atmosphere there too, though nothing has been proven yet. Astronomers think this might be a sign of life.

Why is Callisto “dead”?

Many astronomers have referred to Callisto as being a “dead” planet. This is because there is no activity on the planet – there’s no volcanoes on it’s surface. However, in more recent years this planet has been anything but dead. Astronomers believe there might be oxygen in it’s atmosphere, and it might even have an ocean underneath it’s crust.

Why does Callisto glow?

Many people wonder why the moon Callisto seems to glow. It doesn’t actually glow, but this is actually a result of this moons surface. Even though it is old and heavily cratered, Callisto has a lot of ice across it’s surface. This makes it very reflective of the Sun, which makes it look like it is glowing.

Can you see Callisto from Earth?

Due to the ice that is one Callisto’s surface, it is actually quite easy to see Callisto from Earth with a telescope. It is actually brighter than our moon, just a lot further away.


Hopefully you’ve learned some things about the moon Callisto. What was once thought of as a dead moon is now the topic of discussion, as we think it’s atmosphere contains oxygen and it might have water under it’s surface. So, it could have the potential to be able to sustain life, which makes it interesting for astronomers.