In an alternate universe where our solar system's planets went to school, those walking around with graceful rings would most definitely be the gifted popular kids in the class, and for good reason!
Even in our own universe, ring systems are a striking feature. Not all planets are lucky enough to have them, for these rings aren’t easy to handle. They form and exist under very specific conditions, and most of them are found within a critical distance of their host, known as the Roche limit.
Now, scientists have recently spotted a new ring system right at the edge of our solar system! Wrapped around a dwarf planet named Quaoar, this ring is extremely rare because it seemingly does not stick to the Roche limit — a finding that has called into question everything we currently know about ring systems.
Spotting Quaoar’s unique ring system
The icy dwarf planet Quaoar is approximately half the size of Pluto and orbits the Sun beyond Neptune. Due to its size and distance, even the most powerful telescopes see it as only an indistinct blob, so imagine the difficulty of directly imaging its faint and tiny rings!
Astronomers equipped with the extremely sensitive high-speed HiPERCAM could only view the rings in a brief one-minute window, and that too indirectly.
The observation was made possible only when Quaoar blocked the light of distant stars passing in its background, a phenomenon known as stellar occultation. The occultation was preceded and followed by striking dimming in starlight twice, indicating the presence of a ring system around Quaoar.
But what left the astronomers surprised was the continued existence of this ring despite its distance from the parent body going beyond the known norms and theories.
The fancy rings around planets are essentially moons which have failed to coalesce around smaller objects.
For the longest time, this property of ring systems was governed by the Roche limit, which prescribed an outer limit for ring systems. Beyond this limit, the ring would be pulled apart by tidal forces exerted by the parent body and undergo accretion to form moons.
Apart from the well-known ring systems of Saturn, Jupiter, Uranus and Neptune, just two other minor planets (Chariklo and Haumea) are known to host rings. All these ringed worlds conform to the Roche limit, except for Chariklo's rings, which have only stepped a bit beyond the line.
However, Quaoar is a rare rebel who has pushed scientists to rethink the known limits of ring systems. Its ring lies at a distance of over seven planetary radii, which would be around 4023 kilometres.
This is way beyond the Roche limit and twice as far out as what was previously thought to be the maximum radius, which the scientists calculated to be 1770 kilometres!
"It really shouldn't be there. We should look at this limit again and better understand how these satellites are formed," said Dr Bruno Morgado, the lead author of this study.
"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," added Professor Vik Dhillon, the study co-author from the University of Sheffield's Department of Physics and Astronomy.
For us, this discovery is a refreshing reminder that many more such 'science-changing' finds are awaiting discovery. With the development of more advanced telescopes, we are only getting closer to unravelling the incredible treasures hidden in outer space.
This study was published in the journal Nature and can be accessed here.