The dwarf planet Quaoar, located beyond Pluto, might have just gained a new moon or possibly even a third ring. Recent observations by astronomers Rick Nolthenius and his former student Kirk Bender in California suggest intriguing developments in this distant world.
Quaoar and other dwarf planets live far away, making them hard to see directly from Earth. To study them, scientists often rely on stellar occultations. This occurs when a celestial body passes in front of a star and blocks its light. During these moments, any surrounding rings or moons may also obscure the star’s brightness.
Both of Quaoar’s known rings were first discovered through separate occultations. The initial ring was spotted by a group of amateur astronomers. However, observing these events can be tricky. The alignment of the rings, moons, and stars needs to be just right. Plus, the viewer’s location on Earth also matters, as it shifts the viewing angle.
On June 25, 2025, Nolthenius and Bender set up at the Monterey Institute for Research in Astronomy to catch an occultation involving Quaoar. The dwarf planet, about 680 miles wide, would pass in front of a star visible mainly from northern Canada, but they hoped to see one of its rings from California.
As they prepared their telescopes, Nolthenius opted to start recording early, saying, “Who knows what we’re going to see?” Their patience paid off. Just over a second after the expected occultation, one telescope recorded a brief flicker, indicating something blocked the star’s light.
“The profile of the occultation was most consistent with it being a new moon,” Nolthenius later shared. This unexpected finding could reshape our understanding of Quaoar’s environment.
Published in the journal Research Notes of the American Astronomical Society, the findings suggest the possibility of a new satellite circling Quaoar. This aligns with broader trends in astronomy, where discoveries reveal more about the dynamic systems of distant celestial bodies, much like how new moons have been identified around Saturn and Neptune.
Interestingly, Quaoar has a rich history. Discovered in 2002, it takes 286 Earth years to fully orbit the Sun. Named after a creation figure from Tongva mythology, its unique rings raise questions about how such structures can survive over time. They orbit at unexpected distances from Quaoar, prompting scientists to rethink what they know about planetary rings.
While Nolthenius and Bender suspect the observed signal is a moon, they remain cautious. Other possibilities, such as a torus of material or even a third ring, have not been entirely ruled out. To explore these potential findings further, they continued their observations for an additional three minutes after the expected occultation event.
Benjamin Proudfoot, an astronomer at the University of Central Florida involved in the study, has also been looking into Quaoar. His research using NASA’s James Webb Space Telescope supports the possibility of the newly detected moon being at least 19 miles wide, moving in a unique orbital path around Quaoar. If confirmed, this discovery could deepen our understanding of how moons stabilize their planetary systems.
The search for the new moon will be challenging, as astronomers will need to chart its possible orbit without knowing its exact location in the sky. Proudfoot noted, “It’s on the bleeding edge of detectability,” highlighting the difficulty of observations in such a vast universe.
For now, Nolthenius hopes more observers will join in hunting for Quaoar’s occultations. Presently situated among numerous stars, the dwarf planet’s complex dance will become less frequent as it moves on, making now an exciting time for stargazers. If the new moon is officially recognized, Nolthenius is eager to name it, considering someone special but uncertain how to adhere to naming conventions set by the International Astronomical Union.
As they continue to seek out these celestial events, Nolthenius finds joy in the adventure. “It’s a little microadventure,” he reflected, showcasing the blend of science and discovery that characterizes stargazing and research.
