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A team led by Carnegie’s Scott S. Sheppard has found 20 new moons orbiting Saturn. This brings the ringed planet’s total number of moons to 82, surpassing Jupiter, which has 79. The discovery was announced Monday by the International Astronomical Union’s Minor Planet Center.
Facts about the new moons
Each of the newly discovered moons is about five kilometres, 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.
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.
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 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 newly announced 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 farthest 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
The other newly found 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 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. 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.
The telescope was used
The new moons were discovered using the Subaru telescope atop Mauna Kea in Hawaii. The observing team included Sheppard, David Jewitt of UCLA, and Jan Kleyna of the University of Hawaii.
Using some of the largest telescopes in the world, we are now completing the inventory of small moons around the giant planets, they play a crucial role in helping us determine how our Solar System’s planets formed and evolved.
Contest: Name the moons
Last year, Sheppard discovered 12 new moons orbiting Jupiter and Carnegie hosted an online contest to name five of them. Contest details are available here: https://carnegiescience.edu/NameSaturnsMoons
Understand the contest rules
Most of the outer moons of Saturn are classified into three different clusters depending on their angle of inclination to their orbital path to the planet and the distance from the planet.
- Inuit group — Two of the three prograde moons discovered fit into this outer group with at an orbital inclination of 40–50 degrees to Saturn with a distance of 11–18 million kilometres from the planet. Before this discovery, there were 5 moons in this group named after the creatures of the Inuit mythology.
- Gallic group — The other prograde moon sits furthest out (30–40 million kilometres) from Saturn in this group, and has a shallower orbital angle of 36 degrees. This group had four members before the latest addition. The moons in this group are named after the characters of Gallic mythology.
- Norse group — The rest of the 17 retrograde moons will be joining the current 29 members of the Norse group — mostly named after the giants in Norse mythology.
You can get to name all these moons. The only catch is that you have to name them based on the Gallic, Norse, or Inuit mythology depending on which group they fall into. Submissions for the names can be tweeted to @SaturnLunacy till December 6, 2019.
I was so thrilled with the amount of public engagement over the Jupiter moon-naming contest that we’ve decided to do another one to name these newly discovered Saturnian moons. This time, the moons must be named after giants from Norse, Gallic, or Inuit mythology.