New observations have thrown astronomers for a loop after they found a strange ring circulating a Pluto-sized dwarf planet that dwells in the outer reaches of the solar system.
The planet, called Quaoar, was being observed by astronomers using the La Palma telescope when they spotted a ring much further from Quaoar than what is typical for celestial bodies. The results of the research were published in the journal Nature.
Now, astronomers like professor Vik Dhillon from the University of Sheffield’s department of physics and astronomy are questioning what they know about how ring systems form.
Dhillon was one of the co-authors of the recently published observations, and he shared with The Guardian that the group of researchers was surprised by what they observed.
“The ring came as a real surprise, and doubly surprising was where it was, well outside the theoretical maximum for where a ring can survive according to classical theory,” Dhillon said. “These are the most unusual rings we’ve seen.”
Quaoar orbits the sun beyond Neptune, and astronomers say that it is too distant and the ring is too narrow to be seen directly. The ring system was only made detectable during an occlusion event, when the planet passed in front of a star giving it a sharp silhouette, making it briefly observable from Earth’s telescopes. However, the discovery wasn’t by chance, as Dhillon says they were prepared.
“Astronomers who work in this area predict these occultations to the second, years in advance,” Dhillon told the media outlet. “One of these was predicted, and we were on the observatory on La Palma.”
While the planet caused a dip in light as it passed in front of the star, there were also two smaller dips before and after, leading to the discovery of the ring system.
The ring is orbiting the planet at a distance of more than seven planetary radii, twice as far out as the previously known maximum limit, referred to as the Roche limit. The rings orbit the planet at more than twice the Roche limit that Saturn’s ring system orbits it.
“What is so intriguing about this discovery around Quaoar is that the ring of material is much farther out than the Roche limit,” Giovanni Bruno, an astronomer at Italy’s National Institute for Astrophysics and one of the authors of the paper, said in a European Space Agency statement. “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.”
Inside the Roche limit, a planet exerts strong-tidal forces, which prevent debris in the ring from becoming a moon.
Anything beyond the Roche limit has the chance of becoming a moonlet formation within decades, as denser regions of rock and ice clump together, pulling more debris into the clump, according to the theories.
The team of astronomers is currently exploring various possibilities for how the distant ring could remain stable and not be forming into a moonlet or form. One possibility is that the debris isn’t “sticky” enough, making the debris bounce off each other.
“If they have a really frosty ice coating, then you can get quite an elastic collision, like hailstones colliding rather than snowflakes,” Dhillon said. “Everyone learns about Saturn’s magnificent rings when they’re a child, so hopefully, this new finding will provide further insight into how they came to be.”