Astronomers discover record-breaking 62 moons around Saturn

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A Canadian-led team of astronomers has discovered 62 moons around Saturn, the largest such trove of planetary satellites ever revealed in one batch.

The find, announced on Thursday, raises the official count of Saturn’s retinue of moons to 145. That easily tops the 95 confirmed satellites circling Jupiter and makes Saturn the solar system’s reigning moon king.

“I am pleased to see so many new objects,” said William Bottke, planetary scientist with the Southwest Research Institute in Boulder, Colo., who was not involved in the find. “Many of them may be fragments from bigger objects, so their properties may tell us about the nature of the interiors of larger captured objects now long gone.”

All of the new objects are thought to be small icy bodies that range in size from 2.5 to eight kilometres across. They are located mostly on the periphery of the Saturn system, with distances that average between 10 and 21 million kilometres away from the planet and its spectacular ring system. The majority of the moons were spotted for the first time in data gathered by the Canada-France-Hawaii Telescope atop Mauna Kea in 2019 and 2020.

“When we did the initial search, we found a whole bunch of things moving with the planet for short periods of time. But we didn’t know their orbits,” said Brett Gladman, a team member and astronomer at the University of British Columbia. “The last couple of years of work has been repeating the search process over and over again to connect the dots and figure out how they’re moving.”

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Much of the painstaking work behind the discovery was conducted by Edward Ashton, then a PhD student at UBC and now a postdoctoral researcher at the Academia Sinica Institute of Astronomy in Taiwan.

To image the faint moons, Dr. Ashton employed a technique known as “shift and stack,” which requires moving the telescope to anticipate where a potential unseen moon may be heading and allowing its light to repeatedly strike the same camera pixel until it exceeds the threshold of detection.

The 62 moons discovered with this method fall into distinct orbital groups, some of which are retrograde – meaning they are circling counter Saturn’s direction of spin. This suggests that they did not form as they are but instead are the remains of a larger moon that was destroyed in a collision some time in the past 100 million years – a relatively recent event by solar system standards.

Dr. Bottke said that picture fits with the idea that Saturn’s outermost moons began as objects that where ensnared by the planet’s gravitational pull early in the solar system’s history.

“We believe they experienced intense collisional evolution from that time, with the objects surviving to today being fragments of a highly decimated population,” he said.

Dr. Gladman said that the UBC team was motivated by growing evidence that Saturn has more moons at each size category than Jupiter, presumably as a consequence of the latest collision or collisions. This has been borne out by the new discoveries, which suggests that as still tinier and more numerous objects are found orbiting around each planet, Saturn’s lead in the moon count will only grow.

“Jupiter is never going to reclaim the crown,” Dr. Gladman said.

Saturn’s largest moon, Titan, was discovered in 1655 by Dutch astronomer and mathematician Christiaan Huygens, who was also the first to realize that the planet was surrounded by ring-like structure of mysterious origin. Over the next two-and-a-half centuries, nine more moons would be added to the list as telescopes improved. Nine more followed between 1967 and 1990, including three discovered by the Voyager 1 spacecraft as it flew past Saturn in 1980.

Voyager confirmed that Saturn’s rings are made of countless individual particles that range in size from snowflakes to house-size boulders. But the race to discover all objects of significant size orbiting on the outskirts of the Saturn system – as well as those around other giant planets – was still to come, thanks to the marriage of large telescopes and wide field digital cameras.

Dr. Gladman became one of the early pioneers of that race starting in 1997 when he co-discovered five moons around Uranus. In the years since he has been involved in the discovery of another 21 satellites, mostly around Jupiter and Saturn. With this week’s announcement, he has more than tripled the number of celestial objects that include his name as a co-discoverer.

In addition to illuminating the history of the Saturn system, the discovery of so many additional moons around Saturn provides a practical benefit for space exploration.

“Spacecraft need to know where the moons are so that they can avoid colliding with them during close flybys, or alternatively if they want to point their instruments to get the science data,” Marina Brozovic, a physicist with NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

And from another perspective, Dr. Brozovic said, the find underscores something that has been true of the solar system’s sixth planet ever since the telescope was invented.

“It is showing us what a wonder-world Saturn really is.”