Jupiter is a superstar in our solar system. It’s the biggest, it’s wonderfully gassy, and it now has the most documented moons, clocking in at 92 natural satellites. Its new count became official on January 20, 2023, when the Minor Planet Center recognized the last of a batch of 10 newly identified moons. Jupiter is stealing the title from Saturn, which only has 83 documented moons.
Until 2017, Jupiter had just 67 moons on record. But in 2017 and 2018, astronomer Scott Sheppard of the Carnegie Institution for Science and his team identified a dozen previously unknown moons orbiting Jupiter, bringing its total to 79—just shy of Saturn’s 83. In 2021 and 2022, they found three more. Now, Sheppard and his research team have identified 10 more moons that have been recognized by the Minor Planet Center, the International Astronomical Union’s body studying minor planets.
Sheppard and his colleagues found these newly revealed moons using the Subaru Telescope at the National Astronomical Observatory of Japan in Hawaii and the Victor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory in Chile. The team made sure these objects were actually moons with followup observations using the Magellan 6.5-meter Telescope at the Las Campanas Observatory in Chile. The 10 latest moons vary in size, but all are larger than 3,280 feet (1 kilometer) across, while about half are larger than 4,920 feet (1.5 kilometers).
“We have been surveying for new moons around Jupiter serendipitously while our main survey is looking for planets in the outer solar system beyond Pluto,” Sheppard told Gizmodo in an email. “These moons are yet to be named, as they were just announced. The Minor Planet Center will number these new moons (every moon gets a number once it is determined the orbit is very well known) likely in the next few months and at that time we will be able to name some of them.”
Sheppard explained that Saturn and Jupiter have so many moons because they are fragments of once-larger satellites that broke apart due to impacts with asteroids or other moons. Sheppard hopes that upcoming missions to Jupiter—like the European Space Agency’s Jupiter Icy Moons Explorer or NASA’s Europa Clipper—will be able to provide us with high-resolution images of some of these newly discovered moons.
“The hope is that if we find enough, one of them will happen to just be near the spacecraft’s trajectory for it to get close-up images of it,” he said. “These outer moons are important to understand because they are the last remnants of the population of objects that formed in the giant planet region as the rest of the material was incorporating into the planets.”
The two gas titans of the solar system are likely to remain locked in the battle for most moons. In 2019, the Minor Planet Center recognized 20 more moons surrounding Saturn that Sheppard and his team identified, which brought the planet’s total to 82, surpassing Jupiter’s then-total of 79. In 2021, the Minor Planet Center recognized another moon of Saturn, discovered by researchers led by Edward Ashton, bringing Saturn’s total to the current 83. Jupiter’s reign may not last long, however, as Sheppard told Gizmodo that his team is currently looking for additional moons around Saturn.