A planet believed to have reached its lunar ceiling has just broken the record. A new study has discovered 128 new irregular moons around Saturn, bringing its total to a record-breaking 274, eclipsing the 95 confirmed moons of Jupiter and more than doubled the total number of other planets in the solar system combined.
This discovery was enabled by the “shift and stack” technique, which is an advanced imaging technique highly effective for detecting faint, fast-moving objects. This technique entails taking images of an area of interest over time and then shifting them through software based on predictions of where a possible lunar object would be moving. By stacking these images, an enhancement of the signal of a possible moon and reduction of noise can enhance enough to spot objects as small as a kilometer or so in size. This study, spearheaded by Dr. Edward Ashton of Academia Sinica in Taiwan, utilized their Canada-France-Hawaii Telescope to make their observations over many years, correlating many of these discoveries to previous reports of sightings from 2019 to 2021 and even scattered reports from 2004 to 2007.
All the recently cataloged orbits are irregular satellites. These moons are small and potato-shaped residuals of past collisions. Their orbits are highly inclined and retrograde, meaning they orbit Saturn contrary to the direction of Saturn’s rotation. Most of them reside in specific orbital families, especially in the so-called Norse group, which orbits Saturn on highly inclined and extended orbits at a large distance from Saturn. The largest orbital group is in the retrograde subgroup Mundilfari, which is very size-diverse and indicates a catastrophic breakup event roughly 100 million years ago. This would have occurred when bodies like captured moons with diameters of tens of kilometers broke apart into groups of small bodies.
These discoveries can now be allied with other models of moon formation for giant planetary bodies. As was previously explicated for other discoveries on irregular moons, irregulars are modelled to have originated from captured planetesimals during the early Solar System era. This was owing to the chaotic movements of giant planetary bodies that occurred between 60 to 100 million years after Solar formation. The captured bodies were then susceptible to resonant collisions and cometary impacts. The debris from such collisions now orbits Saturn up to 50 times further than its major regular satellites.
These patterns of clustering, as have appeared in the new survey, are more than simple statistical phenomena; they offer forensic evidence for a violent past for the ringed planet, Saturn. For instance, a Kiviuq family of prograde moons has grown considerably with the addition of a dozen new moons, drawn from a tight clustering around the prograde Kiviuq’s elongated orbital path, originally a possible but now a confirmed collisional family.
The knowledge of these irregular moons also links into the mystery surrounding the rings of Saturn. Some researchers suggest that the rings might be the remnants of destroyed moons, which were shredded apart by tidal forces or destroyed in a catastrophic collision. The close age estimate for the rings and several groups of moons indicates that both might be connected in some way. The moon orbits in Saturn’s system are entwined in such a way that moons can shape the rings, gaps, or even create satellites from ring material.
Although the new discoveries are extending the limits of observation, Ashton observes that technology may very well be approaching an effective limit in terms of finding moons orbiting Saturn, Uranus, and Neptune. Further progress may very well require more sensitive detectors or space missions that allow for a close-range survey.
On the other hand, research in planetary defense has some collateral benefits. The European Space Agency’s Hera spacecraft, which is on its way to investigate the results of NASA’s DART asteroid redirection experiment, just flew by Mars and snapped photos of its small moon, Deimos. One of the objectives of Hera’s mission is to improve the models of kinetic impactors, which are proposed methods of protection against dangerous asteroids for Earth. The same principles of orbital dynamics and collision physics apply to dangerous asteroids.
But for space buffs or astronomers in particular, Saturn’s growing number of moons is anything but a record and much rather a kind of history book of our Solar System, in which the language is formed by the orbits and shapes of several hundred tiny moons. Every single new moon contributes to the history book of our Solar System, adding a detail to the puzzle, which aims to solve the mystery of how our outer planets were formed.
