Saturn and a few of its many moons, as seen by the Hubble Space Telescope. Credit: NASA/ESA/Hubble Heritage Team (STSCI/AURA)/SPL
Astronomers have announced the discovery of 128 new moons orbiting Saturn, raising questions about why the planet has such a huge number of satellites. Investigating this phenomenon could provide us with crucial knowledge about the evolution of the Solar System.
The discoveries bring Saturn’s total moon count to 274, nearly triple Jupiter’s and more than the total number of known moons around the other planets.
“Saturn is the king of the moons,” says Scott Sheppard, an astronomer at the Carnegie Institution for Science in Washington DC, whose observations provided a starting point for the finding.
The discovery is “fascinating”, says Samantha Lawler, an astronomer at the University of Regina in Canada, who also contributed observations that led to the finding but did not contribute to the forthcoming paper about them. “It just shows how much is out there.”
Many moons
The moons, which were officially recognized this week by the International Astronomical Union, will be described in a paper led by astronomer Edward Ashton at the Academia Sinica Institute of Astronomy and Astrophysics in Taipei, Taiwan. The study will be published in the Research Notes of the American Astronomical Society. Unlike our own Moon, which is 3,475 kilometres wide, these small rocks are just a few kilometres across in size. They swing around Saturn in chaotic, distant orbits, often moving in reverse relative to the planet’s major moons, such as Titan and Rhea.
The moon that made Saturn a pushover
Most of the moons are new discoveries, but observations by Sheppard two decades ago hinted at their existence. From 2004 to 2007, he used the 8.2-metre Subaru Telescope on Mauna Kea in Hawaii to examine patches of space near Saturn and detected faint light from these small, irregular moons. However, many couldn’t be confirmed as moons because their orbits could not be definitively tracked.
Ashton was able to revisit those findings thanks to advancements in discovery techniques and the allocation of more telescope time. From 2019 to 2021, using the 3.6-metre Canada France Hawaii Telescope on Mauna Kea, Ashton confirmed 62 new moons of Saturn by stitching together the telescope’s images to more easily see the faint moons. In 2023, he had more time on the telescope, leading to the latest 128-moon haul.
Saturn’s movements also helped: from our perspective on Earth, the planet has moved out of alignment with the dense star field near the centre of the Milky Way, reducing the number of background stars in our line of sight that could masquerade as moons.