Move over Jupiter; Saturn
is the new moon king. A team has found 20 new moons orbiting Saturn. This
brings the ringed planet's total number of moons to 82, surpassing Jupiter,
which has 79
Carnegie Institution for Science –
October 7, 2019 -- 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.
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.
"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," Sheppard explained.
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," explained Sheppard.
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," Sheppard said. "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 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," says Scott Sheppard. "They play a crucial
role in helping us determine how our Solar System's planets formed and
evolved."
Last year, Sheppard discovered 12 new
moons orbiting Jupiter and Carnegie hosted an online contest to name five of
them.
"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," Sheppard
said. "This time, the moons must be
named after giants from Norse, Gallic, or Inuit mythology."
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