Jupiter, Neptune, Uranus, and Saturn all have one major thing in common: they all have rings. Some might not be as visible as Saturn’s rings, but they do exist. Even things like dwarf planets and asteroids have rings. These rings all are specifically distanced from the parent body. Quaoar, however, has rings that fall outside this domain. This makes Quaoar’s rings seemingly impossible.
Quaoar is a dwarf planet. Dwarf planets are planet-like bodies that do not fit all of the requirements to be deemed a planet. Quaoar itself is an icy body smaller than Pluto inside the Kuiper Belt at our solar system's edge. Due to it being so far away, it makes it difficult to research.
Even with these difficulties, Bruno Morgado, an astrologer at Federal University of Rio de Janeiro in Brazil, found a way to gather information about Quaoar. Morgado formed a team to observe when Quaoar blocked the light of a star. This observation revealed details about its size and its own atmosphere.
The researchers used data of Quaoar passing in front of a star from 2018 to 2020. They had telescopes in places like Namibia, Australia, and Grenada. There were also telescopes sending information from space. With all of this information, Morgado figured out that Quaoar has an atmosphere. More importantly, he also discovered that it has its own ring.
Quaoar having its own ring is surprising because the ring is well beyond its Roche limit. A Roche limit is an imaginary line beyond which rings are not supposed to form. Any other planets' rings stay inside of the Roche limit. Being inside the limit is what keeps the rocks from forming into a moon.
There could be three possibilities why Quaoar’s rings are so far out. One explanation could be that Morgado’s team saw the ring before it turned into a moon. However Morgado says that this is unlikely. Another explanation could be that Quaoar’s moon, Weywot, is keeping the ring in place with its gravity. The last explanation could be that the ring's particles are colliding in a way that keeps them from becoming a moon. To do this, the particles would have to be extremely bouncy. To test which might be true, scientists will need to make models of these scenarios sometime in the future.
Making observations and basing theories on them is how Kuiper Belt research is conducted. Everything in the Kuiper Belt has been discovered, not predicted. This goes against classical sciences where predictions are made first and observations come afterwards to confirm or deny an idea. However, observing more situations like Quaoar’s rings could be helpful. In the future, this might add to the planetary information we already have.
[Sources: Science News Explores; European Space Agency; NASA]