Astronomers using the Subaru Telescope in Hawaii have found 20 new moons orbiting Saturn. The discovery brings the total number of known Saturnian moons to 82, surpassing Jupiter, which has 79. To offer the general public a chance to get involved in naming the new moons, the Carnegie Institution for Science launched a contest on October 7, 2019.
An artist’s conception of the 20 newly-discovered Saturnian moons. Image credit: Carnegie Institution for Science.
“Using some of the largest telescopes in the world, we are now completing the inventory of small moons around the giant planets,” said team leader Dr. Scott Sheppard, an astronomer with the Carnegie Institution.
“They play a crucial role in helping us determine how our Solar System’s planets formed and evolved.”
Each of the newly-discovered Saturnian moons is about 3 miles (5 km) in diameter.
Seventeen of them orbit the ringed 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 it. The more-distant retrograde moons and one of the prograde moons each take more than three years to complete an orbit.
“Studying the orbits of these moons can reveal their origins, as well as information about the conditions surrounding Saturn at the time of its formation,” Dr. Sheppard said.
The outer moons of Saturn appear to be grouped into three different clusters in terms of the inclinations of the angles at which they are orbiting around the planet.
Two of the newly-discovered prograde moons fit into a group of outer moons with inclinations of about 46 degrees and are called the Inuit group, as they are named after Inuit mythology. These moons may have once comprised a larger moon that was broken apart in the distant past.
Likewise, the new retrograde moons have similar inclinations to other previously known retrograde Saturnian moons, indicating that they are also likely fragments from a once-larger parent moon that was broken apart.
These retrograde moons are in the Norse group, with names coming from Norse mythology. One of the newly-discovered retrograde moons is the furthest known moon around Saturn.
“This kind of grouping of outer moons is also seen around Jupiter, indicating violent collisions occurred between moons in the Saturnian system or with outside objects such as passing asteroids or comets,” Dr. Sheppard noted.
The other newfound prograde moon has an inclination near 36 degrees, which is similar to the other known grouping of inner prograde moons around Saturn called the Gallic group. But this new moon, dubbed S/2004 S24, orbits much farther away from Saturn than any of the other prograde moons, indicating it might have been pulled outwards over time or might not be associated with the more inner grouping of prograde moons.
If a significant amount of gas or dust were present when a larger moon broke apart and created these clusters of smaller moon fragments, there would have been strong frictional interactions between the smaller moons and the gas and dust, causing them to spiral into the planet.
“In the Solar System’s youth, the Sun was surrounded by a rotating disk of gas and dust from which the planets were born,” Dr. Sheppard said.
“It is believed that a similar gas-and-dust disk surrounded Saturn during its formation.”
“The fact that these newly-discovered moons were able to continue orbiting Saturn after their parent moons broke apart indicates that these collisions occurred after the planet formation process was mostly complete and the disks were no longer a factor.”
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This article is based on text provided by the Carnegie Institution for Science.
