The odd dwarf planet Quaoar may need a brand-new moon. Observations of the tiny world, made by a pair of astronomers in California, counsel it possesses both a second satellite tv for pc or a 3rd ring.
Quaoar and our photo voltaic system’s different dwarf planets are usually so far-off that they’re a problem to view instantly from Earth. (An exception is Ceres, which lies in the primary asteroid belt between Mars and Jupiter.) So, to watch them, astronomers depend on stellar occultations — moments when an object passes between them and a background star. The physique of the foreground object briefly blocks mild from the star, as do any rings or satellites.
Each of Quaoar’s recognized rings had been found in separate occultations, with the first ring initially identified by a trio of amateur astronomers.
But occultation observations can be tricky. Seeing rings depends on the angle of their orbit, which can miss the star completely. And moons must be in the right position in their journey around their parent object to block the star, so spotting them can be hit or miss. And occultations themselves depend on the viewer’s location on Earth, as the viewing angle shifts with latitude.
On June 25, 2025, Rick Nolthenius, an astronomer at Cabrillo College in Aptos, California, and his former student, amateur astronomer Kirk Bender, set out to observe the Quaoar system during an occultation. The roughly 680-mile-wide (1,090 kilometers) dwarf planet would pass in front of the background star at an angle visible only to observers in northern Canada and other parts of the Arctic during daylight hours. But one of the rings might manage an occultation that could be seen from California. It was enough to send Nolthenius and Bender south to the Monterey Institute for Research in Astronomy, where an observing partnership was set up.
With Nolthenius on the institute’s 36-inch telescope and Bender on the 14-inch one, they anxiously awaited the potential passage.
“I did decide to start the recording earlier,” Nolthenius told Space.com. “I thought, Who knows what we’re going to see?”
So they had their separate systems up and running four minutes before the anticipated occultation. Their optimism paid off.
“I said, ‘Oh my God, did you see that? The star disappeared,'” Nolthenius said.
It was a brief flicker, lasting just over a second, and Bender hadn’t seen it. But both telescopes did. The recordings showed a brief 1.23-second blip.
“The profile of the occultation was most consistent with it being a new satellite — a new moon — going around Quaoar,” Nolthenius said.
The results were published this past August in an article in the journal Research Notes of the American Astronomical Society.
‘Hold recording’
Quaoar was found in 2002. The dwarf planet orbits past Pluto, taking 286 Earth years to finish one lap of the solar. Its title comes from the creation mythology of the Tongva folks, who’re indigenous to the Los Angeles Basin, the place the preliminary observations had been made. The title could be pronounced with two syllables (/ˈkwɑːwɑːr/) or three (/ˈkwɑːoʊ(w)ɑːr/).
In 2007, Quaoar’s solely confirmed moon, named Weywot, was noticed. The dwarf planet’s rings are a puzzle. The pair orbit a major distance from the icy world, farther out in relation to the dwarf planet’s dimension than anticipated. Their in depth attain required astronomers to revise what they thought they knew concerning the survival of planetary rings.
It is attainable that the brand new observations by Nolthenius and Bender point out not a moon however a 3rd ring. The duo have been cautious of their classification, permitting for the chance {that a} torus of fabric may very well be behind the observations. However Nolthenius does not assume that is doubtless.
“As quickly as I noticed that occultation, I made a decision, OK, we will maintain recording,” he stated.
The pair continued to watch for a full three minutes after the deliberate occultation time, for a complete time of 9 minutes. They noticed no signal of a second occultation, which they might have anticipated had a hoop been concerned. Nonetheless, the duo nonetheless does not rule a hoop out as a chance.
Examine co-author Benjamin Proudfoot, an astronomer on the College of Central Florida, additionally thinks {that a} newfound satellite tv for pc is the more than likely rationalization. Proudfoot noticed Quaoar in 2024 utilizing NASA’s James Webb Space Telescope, work that allowed him to place constraints on the ring system in a paper published earlier this year in The Planetary Science Journal.
“We predict we discovered a brand new moon,” Proudfoot advised colleagues in July on the Progress in Understanding the Pluto Mission: 10 Years after Flyby convention in Laurel, Maryland, the place he reported the invention.
Checking the containers
Rings and moons aren’t the one potential explanations for blockages seen throughout occultations. Nolthenius and his colleagues needed to rule out a number of different prospects.
Maybe the best was an airplane flying overhead. Along with Nolthenius and Bender, a handful of different observers had been current, and so they watched the world of the sky for plane; none had been noticed within the area through the occultation. A big chicken may theoretically block each telescopes, and Nolthenius stated that California condors are native to the area. However “they do not hover,” he stated, and that may be obligatory to dam each telescopes for greater than a second.
What a few drone, which may simply handle the feat? Nolthenius identified that such a craft must be very giant, a minimum of 80 inches (200 centimeters) vast, and must be exactly focused to hover in such a means that it could block each telescopes — in different phrases, despatched to “mess with these astronomers.” It must transfer into place, cease on a dime, stay for lower than two seconds, after which go away.
“That may take a drone mastery past what I feel is feasible,” Nolthenius stated.
The group then vetted objects past Earth. Satellites orbiting our planet would block out light for less than a second. Interference by known asteroids would have been identified by the International Occultation Timing Association, which offers instances to events for occultations world wide.
What about unknown asteroids? An asteroid that has remained undiscovered so far would have produced a shorter occasion, and it could be unlikely to dam mild utterly, based on the researchers.
The ultimate potential obstructor was the Quaoar’s recognized moon, Weywot. Nevertheless it was casting its shadow additional south, from an observer’s perspective; occultations it might have produced would have been seen from Costa Rica, not California.
In accordance with Proudfoot’s calculations, the newfound Quaoar moon — if it does certainly exist — is a minimum of 19 miles (30 km) vast. It seems to be shifting in a particular orbit often called a resonance with the outermost ring, making three journeys round Quaoar for each 5 made by the annulus. These numbers are tough estimates, as a result of they’re primarily based on a single remark.
Full affirmation will come as different astronomers make observations of the moon. However that may very well be a problem.
“Proper now, now we have a fairly good concept of what its orbit ought to seem like, however not the place alongside that attainable orbit it may very well be,” Proudfoot advised House.com by e-mail. Observing it once more would primarily require a blind search. He stated it is doubtless that the moon is barely seen in a telescope like Webb when it’s farthest from Quaoar, making it much more difficult to watch.
“It is on the bleeding fringe of detectability,” Proudfoot stated.
Nolthenius hopes that extra astronomers – professionals and amateurs – will flip their eyes to the skies to watch Quaoar’s occultations. Proper now, the dwarf planet is passing in entrance of a area of the sky full of stars. As soon as it strikes on, he stated, occultations can be a lot much less widespread for the following 200 years.
If the brand new moon is confirmed, Nolthenius could have the possibility to call it. He indicated that he is contemplating naming it after “somebody particular to me,” however he is undecided learn how to make that work with the Worldwide Astronomical Union’s naming conventions. (Small objects within the outer photo voltaic system are usually named after deities related to the underworld or creation). Regardless, affirmation will doubtless take a while.
In the meantime, each Nolthenius and Bender will proceed trying to find occultations of Quaoar and different targets. The pair plan to watch greater than 100 occultations this yr, roughly the identical quantity they hunted final yr.
“It is a little bit microadventure,” Nolthenius stated of occultation looking. “I get to go off and do some science and never take into consideration anything.”
