For years, it seemed like Jupiter and Saturn were in serious competition to be the planet with the most moons, with the title swapping from one planet to the other with each discovery of previously undetected natural satellites.
Yet the most recent findings have put Saturn into the lead, with the discovery of 128 new moons. Now, not only does Saturn, with 274, have many more than Jupiter (which has 95 confirmed moons), but it has more natural satellites than the rest of the solar system put together.
The moons were detected by an international team of researchers based in Canada, the United States, France, and Taiwan, led by Dr. Edward Ashton of the Institute for Astronomy and Astrophysics at Taiwan’s Academia Sinica. Although the findings are yet to be peer-reviewed, they’ve been recognized by the International Astronomical Union.
To discover the new moons, the researchers used the “shift and stack” technique to combine multiple overlapping images taken by the powerful Canada-France-Hawaii Telescope (CFHT) at Mauna Kea between 2019 and 2021, then revisited the same sky fields around Saturn in 2023. By combining sequential images of orbital paths, they were able to make the moons bright enough to detect.
All of Saturn's 128 new moons are classified as “irregular.” Unlike the popular conception of a large, mostly spherical object orbiting a planet, these moons are tiny, measuring just a mile or two in diameter and lacking a regular, roundish shape. They orbit in retrograde (i.e., in the opposite direction of Saturn’s rotation) and travel around the planet in elliptical orbits beyond Saturn’s rings.
The most likely explanation for this group of moons is that they are fragments of larger objects captured by Saturn’s gravitational pull early in the planet's history (possibly around four billion years ago) that crashed into each other or were struck by passing comets. This could have happened as little as 100 million years ago, which is quite recent in astronomical terms.
Fly me to the moons:
- Most of the new discoveries are located in a group of Saturn’s moons named for figures in Norse mythology, though some are found in the groups named for Gallic and Inuit deities, prompting astronomers to wonder whether enough names can be found in the respective pantheons for the new moons.
- The new discovery raises an obvious question: what makes a moon a moon, and when is it simply a tiny rock fragment? For now, there is no lower size limit to what can be called a moon as long as it has a traceable orbit around another celestial body.
- For now, the tally of moons in the solar system is:
Mercury: 0
Venus: 0
Earth: 1
Mars: 2
Jupiter: 95
Saturn: 274
Uranus: 28
Neptune: 16
