Astronomers Discover Potential New Moon of Dwarf Planet Quaoar
Astronomers have potentially identified a new moon orbiting the dwarf planet Quaoar, located beyond Pluto. Observations conducted by Rick Nolthenius, an astronomer at Cabrillo College, and his former student, amateur astronomer Kirk Bender, suggest the presence of either a second moon or a third ring around Quaoar. These findings were announced following a stellar occultation event, where Quaoar passed in front of a background star, briefly obscuring its light.
Observing distant celestial bodies like Quaoar is challenging due to their vast distances from Earth. Most dwarf planets are located far beyond the main asteroid belt, which includes only one observable dwarf planet, Ceres. To study these distant objects, astronomers often rely on stellar occultations, which occur when a celestial body blocks the light from a star. This technique can reveal information about rings and satellites, although it depends heavily on the precise alignment of the objects involved.
On June 25, 2025, Nolthenius and Bender set up their telescopes at the Monterey Institute for Research in Astronomy to observe Quaoar during an occultation. The dwarf planet, approximately 1,090 kilometers wide, was expected to block a star’s light, visible only from parts of northern Canada and other Arctic regions during daylight. Anticipating the event, Nolthenius initiated recording four minutes ahead of time.
Their efforts were rewarded when both telescopes detected a brief flicker lasting just over 1.23 seconds. Nolthenius remarked, “I said, ‘Oh my God, did you see that? The star disappeared.’” This flicker suggested the possibility of a new satellite orbiting Quaoar, marking a significant development in the study of this distant dwarf planet.
The findings were published in August 2023 in the journal Research Notes of the American Astronomical Society. Quaoar, discovered in 2002, takes approximately 286 Earth years to complete one orbit around the sun. Its name is derived from the creation mythology of the Tongva people, indigenous to the Los Angeles Basin, where the initial observations were made.
Insights into Quaoar’s Rings and Moons
Quaoar has one confirmed moon, Weywot, discovered in 2007. The dwarf planet is also known to possess two rings, which orbit at a distance that challenges previous understandings of how such structures can survive over time. The recent observations by Nolthenius and Bender have presented a compelling case for either the existence of a new moon or the presence of a third ring.
The duo has not ruled out the possibility of a torus of material being responsible for the observations. Over three minutes of additional recording after the initial occultation yielded no further signs of a ring, raising questions about the nature of the detected flicker. Benjamin Proudfoot, an astronomer at the University of Central Florida and co-author of the study, believes the evidence leans towards the existence of a new moon. He noted that his observations using NASA’s James Webb Space Telescope earlier in 2024 provided constraints on Quaoar’s ring system.
Proudfoot emphasized, “We think we found a new moon,” sharing his insights at a recent conference focused on the Pluto mission.
Challenges in Confirming the Discovery
Confirming the identity of the flickering object is complex, as astronomers must rule out various potential explanations for the light blockages observed. The team carefully considered mundane possibilities, such as aircraft, birds, or drones, as well as astronomical factors like known satellites and asteroids. Notably, known satellites would not block light for an extended duration, and the shadow cast by Weywot would be further south than the observed region, making it unlikely to have caused the flicker.
According to Proudfoot’s calculations, the hypothesized moon would be at least 30 kilometers wide and potentially follows a unique orbit in resonance with Quaoar’s outermost ring. However, locating the moon for further observation poses a significant challenge. Proudfoot explained that while they have a rough idea of its orbit, pinpointing its exact position requires extensive observational efforts.
As Quaoar currently moves through a star-rich region of the sky, Nolthenius encourages more astronomers, both professional and amateur, to observe its occultations. He noted that after this phase, such events will be rare for the next 200 years. If the new moon is confirmed, Nolthenius expressed interest in naming it, possibly after someone significant in his life, while adhering to the naming conventions set by the International Astronomical Union.
Both astronomers remain committed to their quest for further occultation observations, planning to examine over a hundred similar events this year. Nolthenius described the experience as a rewarding “microadventure,” allowing him to engage in scientific discovery while escaping daily concerns.
The ongoing research into Quaoar’s moons and rings underscores the evolving understanding of our solar system and the potential for new discoveries in the distant reaches of space.
