Stephano, a moon of Uranus

Stephano is one of Uranus’s outer irregular moons and follows a retrograde orbit, meaning it travels in the opposite direction to Uranus’s rotation. With an estimated diameter of just 32 kilometres (20 miles), it is a small, faint satellite that was only discovered relatively recently.

Stephano was first spotted in 1999 by a team of astronomers led by Brett J. Gladman, using images captured by the 8.2-metre Subaru Telescope at Mauna Kea Observatory, Hawaii. Its great distance from Uranus, combined with its tiny size, makes it one of the more difficult Uranian moons to observe.

Like other irregular moons, Stephano is thought to be a captured object, possibly originating from the Kuiper Belt or the outer Solar System before Uranus’s gravity trapped it. Its orbit is inclined and elongated, adding to the evidence of a capture origin rather than formation alongside the regular moons.