Saturn and Jupiter, the two gas giants, have long vied for the title of “moon king.” Over the years, astronomers have been slowly discovering tiny moons orbiting both. These discoveries sometimes changed the ranking, like in a race to see which planet can capture moons. But now, it’s not even close anymore.
Saturn has decisively claimed the crown. With the discovery of 128 new moons, the ringed planet’s total count has soared to 274 — nearly twice as many as all other planets combined. Jupiter now trails far behind with just 95 confirmed moons.
The discovery, made by an international team of astronomers using the Canada-France-Hawaii Telescope, cements Saturn’s status as the solar system’s lunar monarch. It’s hard to see now how it could ever be topped.
“Based on our projections, I don’t think Jupiter will ever catch up,” said Edward Ashton, a postdoctoral fellow at Academia Sinica’s Institute of Astronomy and Astrophysics and the lead researcher behind the discovery. His team’s findings were recently recognized by the International Astronomical Union (IAU), the official arbiter of celestial nomenclature.
A Lunar Bonanza
Since 2019, astronomers have been monitoring the sky around Saturn using the Canada-France-Hawaii Telescope. By combining multiple observations to enhance faint signals, they initially identified 62 new moons, along with dozens of other objects that may or may not have been moons. In 2023, they revisited the same patches of sky for three months to confirm that these objects were indeed moons. These amounted to a staggering 128 new additions to Saturn’s lunar family.
To some, calling these satellites moons could sound odd. They certainly don’t look like the familiar Moon around Earth. Most of them are irregular satellites — tiny fragments, just 2 to 4 kilometers in diameter, that likely formed from violent collisions between larger moons or with passing comets. Technically, they’re still moons whether you like it or not. More on that in a moment.
Many of them cluster near the Mundilfari subgroup, a region believed to be the site of a cataclysmic collision within the last 100 million years. “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,” Ashton said.
How Small Is Too Small for a Moon?
How tiny can an object be before it’s no longer considered a moon? The newly discovered satellites are so small that they appear as little more than “fuzzy blobs” in telescope images. Mike Alexandersen of the Minor Planet Center, which logs planetary bodies for the IAU, acknowledges the challenge. “The cutoff between what is a moon and what is just a rock particle is probably going to be somewhere between 1 kilometer and 1 meter in diameter,” he said. “It’s most likely going to be relatively arbitrary.”
The IAU has already decided not to prioritize naming moons smaller than 1 kilometer unless a spacecraft visits them. But for Ashton and his team, the discovery is about more than just numbers. “These are small little rocks floating in space, so some people might not find it quite an achievement,” he said. “But I think it’s important to have a catalogue of all the objects in the solar system.”
Could we find more? Perhaps. However, the current pace of discovery has likely run out of steam. The current technology in detecting moons around distant planets like Saturn, Uranus, and Neptune has reached its limits. But the search is far from over. Advances in telescope technology could reveal thousands of moons in the coming decades.
Elizabeth Day, a planetary scientist at Imperial College London, notes that mapping these objects may, at some point, carry important practical considerations — even financial ones. “We might want to extract resources from asteroids and moons in the solar system, so having a great understanding of what is where is important for that,” she said.
For now, the ringed planet reigns supreme — but the cosmos always has more secrets to reveal.
