Astronomers discover a strange ring around this little planet
A mini-planet called Quaoar has taken astronomers by surprise. The cold planet, which was discovered in 2022, has a ring of dust and debris, similar to Saturn. But the distance at which Quaoar's ring is located is law-defying, per a new study. Quaoar comes under the so-called trans-Neptunian objects group, which includes small planets orbiting beyond the outermost planet Neptune in our solar system.
Why does this story matter?
Quaoar is proposed to be a dwarf planet, but it has not been formally classified as yet by the International Astronomical Union. It has a moon called Weywot, which measures 170 kilometers in width and orbits beyond the ring. The planet, which measures half of that of Pluto, resides in the Kuiper Belt, the doughnut-shaped ring of icy objects in the outer solar system.
Quaoar's ring is located at an unusual distance
Quaoar's ring is located at an unusual distance, 4,100 kilometers away from Quaoar's center, with a diameter of about 8,200 kilometers. According to scientists, given the ring's distance, the planet should not be able to hold the particles suspended in the way it does. Instead, the ring should have aggregated, under its own gravity, to form a moon, like Weywot, but that didn't happen.
Quaoar's ring has surpassed the Roche limit
Quaoar's ring defied what's called the Roche limit and is the first known ring around a celestial body to have surpassed the rule. Roche limit defines the distance within which the gravitational field of a celestial body is strong enough to prevent any smaller body from being held together by gravity. Inside the Roche limit, orbiting material is prone to disperse and form rings.
Quaoar's ring far exceeds the Roche limit
"What is so intriguing about this discovery around Quaoar is that the ring of material is much farther out than the Roche limit," said Giovanni Bruno, an astronomer at Italy's National Institute for Astrophysics (INAF). "As a result of our observations, the classical notion that dense rings survive only inside the Roche limit of a planetary body must be thoroughly revised."
Ringed planets like Saturn and Uranus fall within Roche limit
Talking about our solar system, Saturn has the largest ring system. Other gas planets such as Jupiter, Uranus, and Neptune also have rings. Non-planetary bodies like the asteroid Chariklo and another trans-Neptunian object Haumea also possess rings. But, they all fall within the Roche limit.
How can Quaoar's ring exist?
A ring "made of debris, resulting from a putative disruptive impact into a Quaoar moon, would survive for a very short time-but the probability to observe that is extremely low," said Isabella Pagano, the study's co-author. Pagano added that the theories surrounding the aggregation of icy particles "need to be revised," and particles might not aggregate into larger bodies as quickly as expected.
