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Astronomers have discovered 128 new moons orbiting Saturn, giving it an insurmountable lead in the running tally of moons in the solar system.
Until recently, the “moon king” title was held by Jupiter, but Saturn now has a total of 274 moons, almost twice as many as all the other planets combined. The team behind the discoveries had previously identified 62 Saturnian moons using the Canada France Hawaii telescope and, having seen faint hints that there were more out there, made further observations in 2023.
“Sure enough, we found 128 new moons,” said the lead researcher, Dr Edward Ashton, a postdoctoral fellow in the Institute for Astronomy and Astrophysics at the Academia Sincia in Taiwan. “Based on our projections, I don’t think Jupiter will ever catch up.”
There are 95 moons of Jupiter with confirmed orbits as of 5 February 2024.
The moons have been formally recognised by the International Astronomical Union this week and, for now, have been assigned strings of numbers and letters. They will eventually be given names based on Gallic, Norse and Canadian Inuit gods, in keeping with convention for Saturn’s moons. Most of the new moons fall in the Norse cluster, meaning astronomers are now on the hunt for dozens of obscure Viking deities. “Eventually the criteria may have to be relaxed a bit,” Ashton said.
The moons were identified using the “shift and stack” technique, in which astronomers acquire sequential images that trace the moon’s path across the sky and combine them to make the moon bright enough to detect. All of the 128 new moons are “irregular moons”, potato-shaped objects that are just a few kilometres across. The escalating number of these objects highlights potential future disagreements over what actually counts as a moon.
“I don’t think there’s a proper definition for what is classed as a moon. There should be,” said Ashton. However, he added that the team may have reached a limit for moon detection – for now.
“With current technology, I don’t think we can do much better than what has already been done for moons around Saturn, Uranus and Neptune,” said Ashton.
Closer observations of the bonanza of tiny moons could give scientists a window into a turbulent period in the early solar system, in which the planets migrated around in unstable orbits and collisions were common. The new moons are clumped together in groups, suggesting that many of them are the remnants of much larger objects that collided and shattered within the last 100m years. The moons all have large, elliptical orbits at an angle to those of moons closer to the planet.
“[They] are likely all fragments of a smaller number of originally captured moons that were broken apart by violent collisions, either with other Saturnian moons or with passing comets,” said Prof Brett Gladman, an astronomer at the University of British Columbia.
Understanding the dynamics of Saturn’s many moons could also help resolve questions about the origin of Saturn’s rings, which scientists have suggested could be the aftermath of a moon that was ripped apart by the planet’s gravity.
Separately, the European Space Agency Hera spacecraft will conduct a Mars flyby on Wednesday and come within 190 miles (300km) of its smallest and most distant moon, Deimos. The moon, which is about 7 miles across, is thought to be the product of a giant impact on Mars or an asteroid that was captured in the red planet’s orbit. Hera will also image Mars’s larger moon, Phobos, before continuing its mission to survey an asteroid, Dimorphos, that was deliberately hit with a Nasa probe three years ago.
Once it reaches the asteroid, Hera will perform a detailed post-impact survey to help develop technology that could deflect dangerous asteroids that may collide with Earth in future.
