The moons of Uranus

The close-in drawings look straight down on Uranus’s north pole. The drawing of the outer moons looks down on the plane of the planets instead, because that is the plane those moons keep to. Uranus is drawn to scale with the orbits. The moons are not: at this scale most would be far too small to see, so each is a dot.

One moon, S/2025 U 1, was found by the Webb telescope in 2025. The size of its orbit is known but nobody has yet published where on that orbit it is, so it has a line and no dot.

• Solid dot. A spacecraft has mapped the whole surface.
• Half dot. A spacecraft has seen part of it.
• Ring. Never seen as more than a point of light.
• Pale line. Goes round the usual way, the way the planets go round the Sun: anticlockwise on these drawings.
• Amber line. Goes round backwards. 9 moons do.
• Broken line. The moon can be more than 10° from where we draw it. 2 orbits are like this. The pull of the Sun and of other moons keeps changing these paths, and a simple orbit cannot follow them exactly. For 1 moon we have no run of positions to fit an orbit to, so it has a line and no dot.

Nobody has measured the size of 24 of the 29. Each orbit is a slowly turning ellipse fitted to positions from NASA’s Jet Propulsion Laboratory for the years 2000 to 2040. The list gives how far out each fit can be. Touch a row to pick out its orbit.

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