The moons of Haumea

You are looking straight down on the orbit of Hiʻiaka, from its northern side. Which way Haumea itself is tipped is not well known, so its moon’s path is the surest thing to look down on. Haumea 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.

The ring is about 2,287 km from Haumea’s centre and about 70 km wide. It was found in 2017, when Haumea passed in front of a star and the star blinked out briefly on either side.

• 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. 2 moons do.
• Broken line. The moon can be more than 10° from where we draw it. 1 orbit is like this. The pull of the Sun and of other moons keeps changing these paths, and a simple orbit cannot follow them exactly.

Nobody has measured the size of either. Each orbit is a slowly turning ellipse fitted to positions from NASA’s Jet Propulsion Laboratory for the years 2000 to 2030. The list gives how far out each fit can be. Touch a row to pick out its orbit.

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