Saturn has regained its title of the planet with the most known moons after the discovery of 62 previously unknown satellites, bringing its total to 145 recognized moons. This surpasses Jupiter’s paltry 92 known moons, prompting astronomers to search for more ways to locate small moons orbiting Jupiter and Saturn.
A team led by astronomer Edward Ashton of the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan developed a technique for spotting small moons around giant planets. By shifting and stacking images taken of the moons over several years, the team was able to identify Saturnian moons down to a diameter of just 2.5 kilometers (1.55 miles). These newly discovered tiny moonlets are now allowing astronomers to piece together Saturn’s past.
The criteria for defining a moon, or natural satellite, are fairly broad. The object in question just needs to have a stable orbit around another, larger body that isn’t a star. So planets, dwarf planets, and asteroids can all have their own moons. However, it’s not sufficient just to spot an object near a planet and declare that a new moon has been found. The object needs to be tracked for several orbits to determine if it’s stable.
The shifting and stacking technique had been used to look for moons orbiting Uranus and Neptune and was used to scan the sky around Saturn using the Canada-France-Hawaii Telescope (CFHT), locating what appeared to be previously unknown objects in space. Between then and 2021, the team periodically took observations for three-hour spans, shifting and stacking the resulting images to see if the objects they identified could be moons. They picked out 63 new moons, one of which was announced in 2021. Now, they have painstakingly confirmed the other 62.
All the newly discovered moons belong to the three groups of Saturn’s moons classified as “irregular”. These – clustered into clumps known as Inuit, Gallic, and Norse moons – orbit the planet on large, elliptical orbits at an inclined angle with respect to the “regular” moons of Saturn. Most of the new moons fall into the Norse group, which is the most populous and has the greatest orbital distance of the three. It also orbits in the opposite direction to Saturn’s rotation.
Astronomers have interpreted these groups as evidence of collisions that took place at some point in Saturn’s recent past, leaving behind swarms of smaller moons. The Norse group, according to analysis, could be what’s left after the disruption of a moderately-sized irregular moon.
The discovery of these new moons has demonstrated a technique for spotting small moons around giant planets and has provided astronomers with further insight into the history of Saturn.