Background information
Learning with Lego: «Planet Earth’s in the kitchen!»
by Michael Restin
Growth in the moons of Jupiter and Saturn
23.3.2026
Translation: machine translated
On 16 March 2026, the Minor Planet Center announced the discovery of four more moons of Jupiter and eleven moons of Saturn. They are all small bodies with a diameter of a few kilometres that orbit their parent bodies at a great distance in elliptical orbits.
The moon families of Jupiter and Saturn have seen further additions, as the Minor Planet Centre (MPC) recently announced: four new moons have been announced for Jupiter and eleven for the ringed planet Saturn. This means that Jupiter now has 101 known natural satellites and Saturn a whopping 285. What all these new discoveries have in common is that they are small celestial bodies with diameters of just a few kilometres. They orbit their parent bodies at wide intervals in elliptical orbits, some even in the opposite direction to the rotation of the central bodies.
In the case of Jupiter, two of the moons were first sighted back in 2011, but further observations were needed to determine their orbits with sufficient accuracy for official registration. The other two Jupiter satellites were documented for the first time in 2018 and 2025. The first observations of Saturn were made in 2020 and 2023; follow-up observations were also required here.
The new moons of Jupiter and Saturn currently only have catalogue designations such as S/2011 J 4 or S/2020 S 45. «S/» stands for satellite (moon) and the year for the first observation. The following letter provides information about the affiliation of the object: «J» stands for Jupiter, «S» for Saturn. The last number refers to the number of the moon within a comprehensive list of possible discoveries. Not all of these are ultimately confirmed as real moons.
Let's take a closer look at one of Jupiter's new moons: S/2011 J 4 orbits the gas giant at an average distance of 11.1 million kilometres and takes around 240 days to do so. The eccentricity of its orbit is e = 0.14, making it less elliptical than the orbit of the closest planet to the sun, Mercury, with e = 0.2. The orbital inclination is 27.5 degrees to Jupiter's equator, meaning the moon orbits it in its direction of rotation.
An example of one of Saturn's newly discovered moons is S/2020 S 45: It orbits Saturn at a distance of 24.2 million kilometres and takes a whole 3.84 years (1404 days) to complete one orbit around the gas giant. Its orbital inclination is 173.6 degrees, which means that the moon moves in the opposite direction (retrograde) to the direction of rotation of the gas planet. With an eccentricity of e = 0.126, its orbit also has a clearly elliptical shape.
The Minor Planet Centre in Cambridge, Massachusetts, is officially responsible for the registration of small bodies and moons on behalf of the International Astronomical Union (IAU). New discoveries are announced as part of the Minor Planet Electronic Circulars (MPEC).
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Header image: NASA/JPL-Caltech/Space Science Institute
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