Astronomers Discover 128 New Moons Around Saturn, Solidifying Its Lead

Saturn has strengthened its position as the planet with the largest known family of moons after astronomers officially discovered 128 new moons. The discoveries were officially recognised by the International Astronomical Union (IAU) on 11 March 2025 following years of observations by an international team of researchers from Taiwan, Canada, the United States and France. The newly discovered objects are all small irregular moons, providing scientists with fresh clues about Saturn's violent past and the collisions that shaped its moon system billions of years ago. A study published by the American Astronomical Society titled 'Discovery of 128 New Saturnian Irregular Moons' notes that the findings also shed new light on the evolution of Saturn's irregular natural satellite population, offering a clearer picture of how the planet's moon system changed over billions of years.

The discoveries were made using the Canada-France-Hawaii Telescope (CFHT), where researchers repeatedly observed the region around Saturn between 2019 and 2021. Instead of relying on single observations, they combined multiple images to strengthen the signals from extremely faint objects, allowing them to detect previously unseen moons. That initial survey confirmed 64 moons, but it also revealed many additional objects that could not yet be officially identified. "With the knowledge that these were probably moons, and that there were likely even more waiting to be discovered, we revisited the same sky fields for three consecutive months in 2023," said lead researcher Dr Edward Ashton, a postdoctoral fellow at the Institute for Astronomy and Astrophysics at Academia Sinica, who completed his PhD in astronomy at the University of British Columbia. "Sure enough, we found 128 new moons. Based on our projections, I don't think Jupiter will ever catch up," said Dr Edward Ashton.

Unlike Saturn's larger and better-known moons, the newly recognised objects are all irregular moons. Scientists believe these moons did not form alongside Saturn. Instead, they were captured by the planet early in the Solar System's history before being broken apart by powerful collisions. "They are a few kilometres in size and are likely all fragments of a smaller number of originally captured moons that were broken apart by violent collisions, either with other Saturnian moons or with passing comets," said Dr Brett Gladman, professor in the Department of Physics and Astronomy at the University of British Columbia.

One of the biggest questions surrounding Saturn's irregular moons has been why there are so many small moons compared with larger ones. According to the researchers, the unusually high number of small objects suggests a major collision took place somewhere within Saturn's moon system during the past 100 million years. Although that sounds ancient, it is considered relatively recent on astronomical timescales. Dr Gladman explained that if the collision had happened much earlier, the fragments would have continued colliding with one another until many of them disappeared. Instead, the large number of surviving small moons points to a more recent event. The researchers believe the collision most likely occurred near the Mundlfari subgroup of Saturn's irregular moons. Many of the newly discovered moons are concentrated in this region, making it the strongest candidate for the ancient impact site. "These studies reveal that the giant planets captured some moderate-sized moons more than 4 billion years ago as the giant planets formed, and we are now seeing moons which are mostly the fragments of those originally captured moons," Dr Gladman said.

The latest discoveries are the result of a carefully planned observing campaign spanning several years. By repeatedly studying the same regions of space and combining multiple observations, astronomers were able to identify objects that would have remained invisible in individual images. "Our carefully planned multi-year campaign has yielded a bonanza of new moons that tell us about the evolution of Saturn's irregular natural satellite population," Dr Ashton said. The international research team also included Dr Mike Alexandersen of the Harvard-Smithsonian Center for Astrophysics and Dr Jean-Marc Petit of the Observatoire de Besançon in France.