Callisto

Callisto is covered in more craters than almost anywhere we know.

What it is

Outermost of the four big Galilean moons, and the most cratered object we know of.

Moon: Orbits a planet rather than the star. Every kind of thing there is →

How to find Callisto

Its position moves, so there is no fixed place on a map to point at. The Planetarium works out where it is for your own place and date.

Show me Callisto in tonight's sky

What you will really see

Through a small telescope

A tiny point right beside its bright planet — steady the telescope and wait.

Honest, not glamorous — why the pictures here are drawn.

🔭 See it drawn as it looks through a telescope

Worth knowing about Callisto

Callisto is almost exactly the size of Mercury, though far lighter -- it is half ice. In weight, about 1/56th of Earth. Its day: tidally locked; same as its orbital period, 16.69 days.

Its surface: Its surface is older than almost anything else in the solar system: nothing has resurfaced it, so every crater it ever took is still there.
How it moves: Just under 17 days -- the slowest of Jupiter's four big moons, so it is the one that wanders furthest from the planet.
The machines we sent: Photographed by Voyager and Galileo; ESA's JUICE will fly past it many times.

The numbers

Across	4 821 km
Made of, among other things	water, rock (basalt)

How anyone knows this

Nobody flew a tape measure out there. Every number on this page was worked out from the ground:

What it belongs to

☀️ Everything the Sun holds, in one place

Then go outside

Clear tonight? The Planetarium will show you what is worth a look. Then just go out.

🌙 Plan an evening outside 🌌 Everything else in the sky