The Kuiper Belt is a planet that hosts an impossible ring

The dwarf planet Quaoar has a ring too big for its metaphorical fingers. While all other rings in the Solar System lie within or near the mathematically determined distance of their parent bodies, the Quaoar ring is much more distant.

“For Quaoar, the ring outside of this mode is very surprising,” says astronomer Bruno Morgado of the Federal University of Rio de Janeiro. The discovery may reflect the rules governing planetary rings, Morgado and colleagues in a study published on February 8. nature.

Quaoar is an icy body about half the size of Pluto that lies in the Kuiper Belt at the edge of the Sun (SN: 8/23/22). So far from Earth, it’s hard to get a clear picture of the world.

So Morgado and his colleagues speculated that Quaoar blocks light from a distant star, a phenomenon called stellar occultation. A Leo star’s twinkle and out of sight can reveal details about Quaoar, such as its size and whether it has an atmosphere.

The researchers received data on occultations from 2018 to 2020, observed from all over the world, including Namibia, Australia and Grenada, as well as space. There was no sign of Quaoar weather. But surprisingly, there was a ring. The discovery makes Quaoar the third dwarf planet or asteroid in the solar system known to have a ring, after the asteroid Chariklo and the dwarf planet Haumea (SN: 3/26/14; SN: 10/11/17).

Even more surprising, “the ring is not where we hope,” Morgado said.

The known circles around other objects lie within or near the so-called Roche limit, the invisible line where the main gravitational force of the peters body is drawn. Within a limit, that force can tear the moon apart, turning it into a ring. Outside, the gravity between the smaller particles is stronger than from the train, and the rings will coalesce into one or more moons.

“We always think about” [the Roche limit] to be right, said Morgado. “The moon is on the other side forming, on the other side the ring is stable. And this way is no longer the way.

For Quaoar in the ring, there are a few explanations, says Morgado. Perhaps observers caught the ring just before it turned right into the moon. But the lucky timing seems inconvenient, he notes.

Perhaps Quaoar’s familiar moon, Weywot, or some other invisible moon provides gravity that somehow keeps the ring stable. Or perhaps the ring particles collide in such a way that they avoid becoming coherent and denser into the moons.

The particles will have to be specially tuned to work, “like a ring of bourbon balls from toy stores,” says planetary scientist David Iudaitt of UCLA, who was not involved in the new work.

The observation is solid, says Jewitt, who helped discover the first objects in the Kuiper Belt in the 1990s. But there is no way to know what the truth of the explanations is, if any, partly because there are no theoretical predictions for such far-out circles to compare with Quaoar’s situation.

That’s on par with the arrival of the Kuiper Belt. “Everything in the Kuiper Belt, basically, was discovered, not predicted,” says Jewitt. “It’s the opposite of the classic training model where people predict things and then confirm or reject them. People discover amazing stuff and explain everything to be ripped off.”

More observations of Quaoar, or more discoveries of apparently alienated circles elsewhere in the solar world, could help show what’s going on.

“I have no doubt that in the near future a lot of people will start working with Quaoar to try to get this answer,” Morgado says.