This page covers 12 moons whose names start with the letter S, ranging from “Sinope” to “Styx.” These moons orbit planets and dwarf planets across the outer solar system, including Jupiter, Saturn, Uranus, Neptune, and Pluto. Most are small, irregular bodies captured long ago by their host planet’s gravity, and together they offer a fascinating window into how planetary systems form and evolve.
Moons are natural satellites that orbit planets or other bodies in space, held in place by gravity. Earth’s Moon is the most famous example, but the outer planets host dozens, sometimes hundreds, of their own — many discovered only in the last few decades thanks to powerful telescopes and wide-field survey cameras. Some of these moons are named after figures from mythology, literature, or indigenous cultures, giving them stories as interesting as their orbits.
Below you’ll find the table with Moon, Parent Planet, Diameter (km), Discovery Year, and Description.
Moon: The name of each moon, so you can quickly identify which natural satellite you’re reading about.
Parent Planet: The planet or dwarf planet each moon orbits, helping you see how these satellites are distributed across the outer solar system.
Diameter (km): The approximate size of the moon in kilometers, giving you a sense of how large or small each body is compared to others on the list.
Discovery Year: The year each moon was first identified, showing you how recent or historical its discovery is and how telescope technology has advanced over time.
Description: A short summary of each moon’s key traits, orbit type, and naming origin, so you can quickly understand what makes it notable.
Moons
Moon
Parent Planet
Diameter (km)
Discovery Year
Sinope
Jupiter
38
1914
Sponde
Jupiter
3
2001
Siarnaq
Saturn
40
2000
Skathi
Saturn
8
2000
Skoll
Saturn
6
2006
Surtur
Saturn
6
2006
Suttungr
Saturn
7
2000
Setebos
Uranus
48
1999
Stephano
Uranus
32
1999
Sycorax
Uranus
150
1997
Sao
Neptune
44
2002
Styx
Pluto
16
2012
Descriptions
Sinope
One of Jupiter’s outermost irregular moons, Sinope belongs to the Pasiphae retrograde group and is thought to be a captured asteroid. It was the last of Jupiter’s historically discovered moons to be found by telescope.
Sponde
A tiny irregular moon of Jupiter in the Ananke group, Sponde orbits in a retrograde direction far from the planet. It was found during a wide-field survey using the Canada-France-Hawaii Telescope.
Siarnaq
One of Saturn’s larger irregular moons and the biggest of the Inuit group, Siarnaq is named after a sea goddess in Inuit mythology. It was found during a broad survey of outer planetary moons.
Skathi
A small irregular retrograde moon of Saturn in the Norse group, Skathi is named after the Norse goddess of winter and hunting. It orbits Saturn at a very large distance from the planet.
Skoll
A tiny retrograde moon in Saturn’s Norse group, Skoll is named after the wolf that chases the sun in Norse mythology. It was identified from images taken at telescopes on Mauna Kea, Hawaii.
Surtur
A small retrograde moon of Saturn in the Norse group, Surtur is named after the fire giant of Norse mythology who rules the realm of Muspelheim. It was discovered alongside several other small Saturnian moons.
Suttungr
A small irregular moon of Saturn in the Norse group, Suttungr is named after a giant in Norse mythology said to guard the mead of poetry. It follows a retrograde orbit at great distance from Saturn.
Setebos
An irregular retrograde moon of Uranus, Setebos is named after a god worshipped by Caliban in Shakespeare’s “The Tempest.” It belongs to the Caliban group of outer irregular moons.
Stephano
A retrograde irregular moon of Uranus named after the drunken butler in Shakespeare’s “The Tempest,” Stephano is one of several small outer moons of Uranus discovered in the late 1990s.
Sycorax
The largest known irregular moon of Uranus, Sycorax orbits in a retrograde direction and is named after the witch from Shakespeare’s “The Tempest.” Its reddish color suggests it may be a captured outer solar system object.
Sao
A small irregular moon of Neptune named after a Greek sea nymph, Sao was discovered during a survey using the Canada-France-Hawaii Telescope. It follows a distant prograde orbit around Neptune.
Styx
A small moon of Pluto discovered by the Hubble Space Telescope, Styx is named after the river separating the living world from the Underworld in Greek mythology. It is one of five known moons orbiting Pluto.
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