USA TODAY International Edition
Planet challenges knowledge of space
Scientists learning about dwarf Quaoar
Just on the outskirts of our solar system exists the dwarf planet Quaoar, and recent observations of the planet found a dense ring around it, but scientists can’t figure how – or why – it’s there.
Discovered in 2002, Quaoar exists in the Kuiper Belt, a region in space beyond Neptune where at least 3,000 planets are known to orbit the sun. The planet is about 690 miles wide, making it the seventh largest trans- Neptunian object, while former solar system planets Pluto and Eris are the biggest in the region. Pluto and Eris are now considered dwarf planets. Quaoar is about 4 billion miles away from the sun and takes around 286 years to orbit it, and has a small moon called Weywot.
The recent observations were made by scientists with the European Space Agency from 2018 to 2021 using ground- based telescopes and the agency’s space telescope Cheops. It was during these observations that scientists made the puzzling discovery.
Putting a ring on it
Since Quaoar is so small and far from Earth, scientists observed the planet through a process called occultation, when the planet crossed in front of a succession of distant stars, allowing it to block out light.
Scientists noticed drops in brightness from the planet but weren’t sure if it was because of effects from Earth’s atmosphere. That was when the Cheops satellite came to the rescue, as it was also able to spot the changes in brightness.
“When we put everything together, we saw drops in brightness that were not caused by Quaoar, but that pointed to the presence of material in a circular orbit around it,” Bruno Morgado, lead researcher from the Universidade Federal do Rio de Janeiro, Brazil, said in a statement. “The moment we saw that we said, ‘ Okay, we are seeing a ring around Quaoar.’”
The ring doesn’t fit
It’s not unusual for planets to have rings, especially since Saturn has them. Even dwarf planets like Chariklo and Haumea have rings.
“What makes Quaoar’s ring unique, however, is where it is found relative to Quaoar itself,” the agency said.
Known as the Roche limit, scientists have long believed any object with a gravitational field can’t form a ring beyond a certain distance.
When it gets beyond a certain distance, the objects making up the ring will morph into a moon, according to the theory.
Saturn, Chariklo and Haumea all follow the Roche limit, except Quaoar; the ring is “71⁄ times the radius of
2
Quaoar,” meaning it’s past the Roche limit and should have formed into a moon.
Why does Quaoar have a ring?
Scientists have not yet understood why the planet has a ring and hasn’t morphed into a moon.
The leading theory is the icy planet has such frigid temperatures that it’s preventing particles from sticking together.