Saturn now has 145 known moons

Using ground-based images analyzed in a new way, astronomers have discovered an additional 62 small moons orbiting Saturn, giving the ringed gas giant a total of 145 known moons.

The data used by the team was collected between 2019 and 2021 in three-hour spans by the Canada-France-Hawaii Telescope (CFHT) on top of Maunakea in Hawaii. It allowed the astronomers to detect moons around Saturn as small as 1.6 miles (2.5 kilometers) in diameter. That’s about two-thirds the length of Hollywood’s Walk of Fame.

Though some of the moons had been spotted as early as 2019, it takes more than sighting an object close to a planet to confirm it is a moon and not an asteroid making a brief close passage to that planet. To change these objects from “suspected moons” to “confirmed moons” of Saturn, the astronomers had to track them for several years to ensure each is actually orbiting the gas giant.

Performing a painstaking process of matching objects detected on different nights over the course of 24 months, the team tracked 63 objects that they ended up confirming as moons. One of these satellites was revealed back in 2021, with the remaining 62 moons gradually announced over the past few weeks.

To a certain extent, this declared number of moons around Saturn is utterly irrelevant. Think about it. Every single object in its rings should be defined as a moon, totaling hundreds of thousands. At some point the question of what defines a moon becomes the relevant question.

Astronomers discover twelve more Jupiter moons

In reviewing ground-based data from 2021 and 2022, astronomers have discovered another twelve Jupiter moons, bringing that planet’s total moon population to 92.

All of the newly discovered moons are small and far out, taking more than 340 days to orbit Jupiter. Nine of the 12 are among the 71 outermost Jovian moons, whose orbits are more than 550 days. Jupiter probably captured these moons, as evidenced by their retrograde orbits, opposite in direction to the inner moons. Only five of all the retrograde moons are larger than 8 kilometers (5 miles); Sheppard says the smaller moons probably formed when collisions fragmented larger objects.

One newly discovered moon, dubbed Valetudo, is about 3,000 feet across and orbits in a retrograde orbit that crosses the orbits of several other moons that orbit in the opposite direction. As the article notes, “This highly unstable situation is likely to lead to head-on collisions that would shatter one or both objects.”

Astronomers find 20 more moons orbiting Saturn

Astronomers have discovered an additional twenty moons orbiting Saturn, bringing the total known to 82, three more than the 79 moons known to circle Jupiter.

Each of the newly discovered moons is about five kilometers, or three miles, in diameter. Seventeen of them orbit the planet backwards, or in a retrograde direction, meaning their movement is opposite of the planet’s rotation around its axis. The other three moons orbit in the prograde—the same direction as Saturn rotates.

Two of the prograde moons are closer to the planet and take about two years to travel once around Saturn. The more-distant retrograde moons and one of the prograde moons each take more than three years to complete an orbit.

The astronomers have also created a contest allowing the public to help name these new moons.

I will make one prediction: They are going to find many more.

In fact, Saturn’s rings and its numerous moons raise the question of what defines a moon. At present, a moon is defined as any object orbiting a planet, regardless of size. With Saturn’s rings however we have millions of objects orbiting that planet, many very tiny. It seems we have never put a size limit on the definition of a moon, and really need to.

Astronomers discover 10 more Jupiter moons

Worlds without end: Astronomers, while searching for objects in the Kuiper Belt, have discovered 10 more Jupiter moons.

All the newfound moons are small, between about 1 and 3 kilometres across. Seven of them travel in remote orbits more than 20 million kilometres away from Jupiter, and in the opposite direction from the planet’s rotation. That puts them in the category known as retrograde moons.

The eighth moon stands out because it travels in the same region of space as the retrograde moons, but in the opposite direction (that is, in the same direction as Jupiter’s spin). Its orbit is also tilted with respect to those of the retrograde moons. That means it could easily smash into the retrograde moons, pulverizing itself into oblivion. It may be the leftovers of a bigger cosmic collision in the past, Sheppard says.

Jupiter’s moons are named after gods with connections to the mythological Jupiter or Zeus. Sheppard has proposed naming the oddball Valetudo, after one of Jupiter’s descendants, the Roman goddess of hygiene and health.

The ninth and tenth newfound moons orbit closer to Jupiter, moving in the same direction as the planet.

I predict that these are not the last moons of Jupiter to be discovered. As our observing skills improve, more are certain to pop up.

Global views of six Saturnian moons

Using images collected after ten years in orbit around Saturn, Cassini scientists have released global color maps of six of Saturn’s icy moons, Mimas, Enceladus, Tethys, Dione, Rhea and Iapetus.

These enhanced colour views have yielded several important discoveries about the icy moons. The most obvious are differences in colour and brightness between the two hemispheres of Tethys, Dione and Rhea. The dark reddish colours on the moons’ trailing hemispheres are due to alteration by charged particles and radiation in Saturn’s magnetosphere. The blander leading hemispheres, the sides that always face forward as the moons orbit Saturn, are all coated with icy dust from Saturn’s E-ring, formed from tiny particles erupting from the south pole of Enceladus.

“Vulcan” and “Cerberus” win the poll to name Pluto’s two unnamed moons.

“Vulcan” and “Cerberus” win the poll to name Pluto’s two unnamed moons. Key quote:

Vulcan was a late addition to the Pluto moon name contenders, and pulled into the lead after Shatner, building on his Capt. James T. Kirk persona, plugged the name on Twitter. Vulcan, the home planet of Kirk’s alien-human hybrid first officer Spock, is not just a fictional world in the Star Trek universe. It is also the name of the god of fire in Roman mythology, and officials at SETI added the sci-fi favorite to the ballot for that reason.

William Shatner proposes naming Pluto’s two unnamed moons Romulus and Vulcan.

William Shatner proposes naming Pluto’s two unnamed moons Romulus and Vulcan.

Astronomers running the Pluto moon naming campaign accepted Vulcan, adding it to the list a day after Shatner suggested it, but Romulus didn’t make the cut. “Mr. Shatner’s second suggestion, Romulus, has a bit of a problem because it is already the name of a moon,” Mark Showalter, an astronomer involved with the competition, wrote in a blog on the Pluto Rocks website on Tuesday. “Romulus, along with his brother Remus, are the names of the moons of the asteroid 87 Silvia. They were discovered by a team led by my good colleague Franck Marchis, now a senior scientist at the SETI Institute.”