How many of Jupiter's moons does COSMOS show?

Four: Io, Europa, Ganymede and Callisto. Jupiter’s known satellite population is much larger, and COSMOS does not attempt a complete inventory of it.

How far are the Galilean moons from Jupiter?

Each has a measured range given above, computed from the Jupiter-centred Horizons archive. Because the orbits are eccentric, a single distance without a date would be misleading.

Why do the moons look like plain spheres?

Because no surface mosaic has passed COSMOS’s validation gate for them yet. Their radii and positions are measured; their appearance is honestly incomplete rather than approximated.

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Jupiter's four Galilean moons: meet Io, Europa, Ganymede and Callisto

The Galilean moons are Io, Europa, Ganymede and Callisto, in order outward from Jupiter. Io is volcanic, Europa has an icy surface, Ganymede is the largest moon in the Solar System, and Callisto is heavily cratered. Compare their orbital distances below, then explore the four moons around Jupiter in 3D.

Explore Jupiter and its four moons

Measured facts

Io · mean distance from Jupiter: 421,769 kmCentre to centre, averaged over daily archive samples. Not a position for tonight.
Europa · mean distance from Jupiter: 671,089 kmCentre to centre, averaged over daily archive samples. Not a position for tonight.
Ganymede · mean distance from Jupiter: 1,070,433 kmCentre to centre, averaged over daily archive samples. Not a position for tonight.
Callisto · mean distance from Jupiter: 1,882,793 kmCentre to centre, averaged over daily archive samples. Not a position for tonight.

Four moons, four different worlds

The names are a useful first step: Io is the innermost of these four, followed by Europa, Ganymede and Callisto. Their surfaces differ greatly, but the current COSMOS moon views are honestly labelled educational spheres—not photographs of those surfaces.

For a simple classroom comparison, open Jupiter, select each moon, and compare its distance with its radius. Then change the explorer date inside the supported archive. You are inspecting Jupiter-centred positions, not predicting how the moons appear from your town tonight.

Io mean radius: 1,821.5 kmPublished physical radius; not the orbital distance.
Europa mean radius: 1,560.8 kmPublished physical radius; not the orbital distance.
Ganymede mean radius: 2,631.2 kmPublished physical radius; not the orbital distance.
Callisto mean radius: 2,410.3 kmPublished physical radius; not the orbital distance.

Why a separate archive is needed

Jupiter is hundreds of millions of kilometres from Earth, while its moons orbit within a couple of million kilometres of the planet. Storing moon positions in an Earth-centred archive would bury a small orbit inside a very large vector, so COSMOS stores them relative to Jupiter and composes the two at runtime.

Each moon gets its own sampling cadence chosen by held-out error, and the archive records the worst position error per moon so the accuracy of a close view is auditable.

Measured distances from Jupiter

The values below are magnitudes of each moon’s Jupiter-centred position vector, sampled daily across the archive window. They are distances from Jupiter, not from Earth, and they change because the orbits are eccentric and perturbed by one another.

Io: 419,988 km to 423,535 km from JupiterMean 421,769 km across 7,306 daily samples.
Europa: 664,442 km to 677,708 km from JupiterMean 671,089 km across 7,306 daily samples.
Ganymede: 1,067,323 km to 1,073,522 km from JupiterMean 1,070,433 km across 7,306 daily samples.
Callisto: 1,868,767 km to 1,896,664 km from JupiterMean 1,882,793 km across 7,306 daily samples.

What is not shown

No surface imagery: Io, Europa, Ganymede and Callisto are true-size educational spheres, and their real surfaces (volcanic plains, ice, grooved terrain, cratered crust) are not rendered.
Jupiter’s smaller inner and outer satellites are not implemented at all; these four are the only moons navigable in COSMOS.
No mutual satellite shadowing, no orbital path lines and no tidal or volcanic activity are modelled.

Sources and further reading

Questions this page answers

How many of Jupiter's moons does COSMOS show?: Four: Io, Europa, Ganymede and Callisto. Jupiter’s known satellite population is much larger, and COSMOS does not attempt a complete inventory of it.
How far are the Galilean moons from Jupiter?: Each has a measured range given above, computed from the Jupiter-centred Horizons archive. Because the orbits are eccentric, a single distance without a date would be misleading.
Why do the moons look like plain spheres?: Because no surface mosaic has passed COSMOS’s validation gate for them yet. Their radii and positions are measured; their appearance is honestly incomplete rather than approximated.

Content updated 2026-10-25. Every value on this page is computed from the shipped datasets; where a source publishes no value, the page says so instead of estimating one.