A team using the telescope atop Mauna Kea in Hawaii has just discovered 128 new moons orbiting Saturn.
Saturn, the sixth planet from the sun, was already the reigning champion of moon-having. A 2023 discovery of 62 new Saturnian moons put it ahead of Jupiter, which takes the silver medal with 95 recorded satellite objects.
Its new count of 274 means Saturn has more moons than every other planet in our solar system combined. This seems rather greedy and possibly bad form.
An image of the ‘Norse Cluster’ of Saturn’s moons. The brightest one shown here is named Suttungr. Photo: NASA/JPL-Caltech/Space Science Institute
The wreckage of older moons
The moons were discovered by layering hours of footage of Saturn and adjusting for the planet’s own movement. The images showed just enough to know an object was there. The moons themselves are not particularly spectacular, at least not in the pictures we have.
They’re blurry chunks of rock of no definite shape or particularly striking colors. These are called “irregular moons” because they aren’t neatly spherical like our moon.
But they were born in dramatic circumstances. The little moons are grouped cliquishly together, suggesting that they used to be part of larger moons that split apart. Violent collisions with each other or with passing comets likely broke them into their current small, irregular clumps. In earlier days of our solar system, when orbits were less stable and arrangements less settled, collisions were common.
The destruction of a large moon probably caused the formation of Saturn’s other claim to fame — its rings. The rings formed between 100 and 200 million years ago, around the same time that scientists estimate the newly discovered irregular moons were formed.
The tiny pinprick of light in the center of this image is one of the 128 new moons of Saturn. Photo: Ashton et al.
When is a moon just a big rock?
These small, irregular moons herald coming debates. Telescopes are becoming more powerful, and scientists are developing better methods to analyze images. As this trend continues, smaller and smaller orbital satellites will be found. Are they all moons? How big does a rock have to be before it can be a moon?
The lead researcher, Edward Ashton, anticipates the moon question. “I don’t think there’s a proper definition for what is classed as a moon. There should be.”
It will probably be up to the International Astronomical Union to make the call on moon identity. Mike Alexandersen, from the IAU’s Minor Planet Center, says that the decision will probably be controversial, like the earlier What is a Planet? debate that led to Pluto’s demotion to a mere “dwarf planet.”
Naming priority for Saturn’s moons will, in the future, go to the largest bodies and those on which craft have landed. For now, none of the 128 new Saturnian moons have names. Most fall within the “Norse cluster,” the section of Saturn’s orbit with objects named from Norse mythology. The rest, following earlier conventions, will be named for Irish and Inuit mythology. With so many left to name and only so many Norse mythological figures, scientists might have to be flexible.
For now, though, Ashton believes they’ve found all the moons of Saturn, Neptune, and Uranus, which can be seen with existing telescopes.
This doesn’t mean that Jupiter will have a chance to catch up, though. Currently, estimates suggest that Saturn has even more small moons to be discovered with better technology in the future. Jupiter may be the biggest planet in our system, but it will have to be satisfied with second place in the moon department.
