Canadian and other researchers have confirmed Saturn as the solar system’s undisputed “moon king," after discovering 128 more moons circling the ringed planet.
The discovery by a team, including current and former University of British Columbia astronomers, brings Saturn's total to 274, almost twice as many as all other planets in our solar system combined, and leaving Jupiter in a distant second place with 95 moons.
"Based on our projections, I don’t think Jupiter will ever catch up," said lead researcher Edward Ashton, who received his astronomy PhD at the University of B.C. and is now a post-doctoral fellow at Taiwan’s Academia Sinica Institute of Astronomy and Astrophysics.
The findings, ratified on Tuesday by the International Astronomical Union, come after a decades-long battle to confirm which of the two biggest planets in the solar system have the most moons.
UBC astronomy professor Brett Gladman, a co-author of a forthcoming paper on the discovery, said it was a "firm result" that Saturn had the most moons.
The new discoveries are only a few kilometres in size, with the smallest ones only two kilometres wide.
Gladman said it's likely they are "remnants" of collisions between larger moons or with passing comets that happened recently in cosmic terms, in the past 100 million years or so.
"The fact that the small moons are still there in enormous abundance tells us the collision couldn't have happened billions of years ago. It must be relatively recent or we wouldn't see the huge abundance of small moons,” said Gladman.
He said if the collisions occurred more than 100 million years ago, then the smaller moons would have ended up being "depleted."
He said a group of the newly discovered moons is located near the so-called Mundilfari subgroup, leading them to suspect that a “catastrophic collision” broke up a now-destroyed moon, leaving behind Mundilfari as the biggest fragment and a large number of the smaller moons on similar orbits.
The discovery of the new moons was made with the Canada France Hawaii Telescope, a 3.6-metre optical telescope on the summit of the dormant volcano Mauna Kea in Hawaii.
The team had previously used the telescope to discover 62 more Saturnian moons, a discovery ratified in 2023 that vaulted the planet past Jupiter's moon tally.
Ashton said that given the understanding there were likely even more moons waiting to be discovered, they revisited the same sky fields from September to November in 2023. These efforts paid off.
Gladman called the latest discovery a culmination of six years of work, as the team pushed technical limits to seek "fainter and smaller moons" around Saturn.
He said they used a “shift and stack” technique, allowing them to add multiple images together to enhance faint signals along known orbital paths.
“It requires a lot of patience, but we're very pleased that the carefully planned campaign has yielded a lot of success,” said Gladman.
The newly discovered moons of Saturn are classified as "irregular moons," referring to objects orbiting giant planets on inclined, highly elliptical and retrograde orbits.
"All of these moons we discovered are in the distant reaches of the bubble of space around Saturn, in which moons can orbit," said Gladman.
The team led by Ashton and Gladman also included Mike Alexandersen of the Harvard Smithsonian Centre for Astrophysics and Jean-Marc Petit of the Observatoire de Besancon.
Could there be more moons out there? Gladman said current technology had been taken as far as possible in the search around Saturn and Jupiter.
He said the new moons are not yet ready to be named, a process that first involves verification of their orbits with the International Astronomical Union.
