Scientists are taking a closer look at Uranus after strange patterns turned up in images from 30 years ago. Engadget reports that researchers looking at data from NASA's Voyager 2—which became the only spacecraft ever to fly by Uranus when it did so in 1986—noticed that the amount of material in some of the planet's rings varies from time time. This pattern of shifting material was present in two of the Uranus' 13 rings, according to Gizmodo. "There's something breaking the symmetry," researcher Matt Hedman says in a press release. He and fellow researcher Rob Chancia believe that something is two undiscovered moons.
The idea is that the two new moons—which would bring Uranus' total up to 29—are orbiting outside the planet's rings, leaving wakes behind them, according to a study being published soon. Similar things called moonlet wakes occur in Saturn's rings. Researchers estimate the new moons circling Uranus are between 2 miles and 9 miles across—smaller than any of Uranus' other moons. "We haven't seen the moons yet, but the idea is the size of the moons needed to make these features is quite small, and they could have easily been missed," Hedman says in the press release. The new moons may also be responsible for keeping Uranus' rings in check, which would explain why they are narrower than those of Saturn. (Another study found Saturn's rings and moons are younger than dinosaurs.)