Dwarf planet Quaoar has a weirdly big ring of debris encircling it

Our solar system’s dwarf planet, Quaoa, has a ring of debris that orbits farther than we thought the laws of physics would allow.

To Alex Wilkins

The dwarf planet Quaoa, located on the other side of Neptune in our solar system, appears to have a ring of debris farther away than previously thought.

“I saw a ring that wasn’t supposed to be there,” said Bruno Morgado of the Federal University of Rio de Janeiro in Brazil.

So far, all rings or orbiting moons observed by astronomers obeyed the limits related to their distance from the parent body put forward by the astronomer Edouard Roche in 1848. When an object is below the Roche limit, the gravitational pull of its parent object rips the orbiting object into clusters of small chunks, eventually forming rings like those seen around Saturn. Outside that limit, dust and debris should coalesce to form larger objects such as the Moon.

At 1110 kilometers in diameter and slightly less dense than our Moon, Qua-or should only be at a distance greater than 2.4 times its 555-kilometre radius, but Morgado and his colleagues place the ring at the radius of Qua-or. Measured at 7.2x. “We’re way past this limit,” he says Morgado.

To find Kua Oa’s capricious rings, the team will observe dwarf planets against various star backgrounds between 2018 and 2021 using Earth-based telescopes and the European Space Agency’s CHEOPS Exoplanet Exploration Space Telescope. bottom. The researchers calculated the ring’s properties using changes in the star’s brightness.

They found that the rings appear to be made mostly of water ice, a bit like Saturn’s F ring. One of the ring’s unusual properties is its irregular shape. Some sections are 5 km wide, others over 100 km. If you stand on the surface of Kua Oa, you should be able to see the widest part of the ring, Morgado said.

It’s not clear why Quaor’s rings are so far beyond Roche’s limit, but the researchers believe that the dwarf planet’s low temperature of -220°C prevents the ring’s contents from coalescing. I think it may play a role.

It is also possible that interactions between particles in the ring, or interactions with Quaor’s satellite Waywot, sustain the ring. More observations of Quaoar and more simulations of the system dynamics will be needed before a definitive answer can be found, says Morgado.

Whatever the answer, you may need to change the Roche limit. This can affect other calculations in astrophysics.

“This concept has been used, for example, to analyze the formation of the moon and the formation of other satellites in the solar system,” Morgado says. “So if we see something that pushes this limit, we need to rethink and better understand why we have this ring.”

Carl Murray of Queen Mary University of London hopes that this won’t change the situation much, as Roche’s limits are only a rough guide, but understanding Quaoar’s anomalous rings will improve it. he says he can.

“Roche limits have their uses, but they don’t really have an exact radius,” says Murray. “It depends on the physical properties of the orbiting matter, and there are other properties that need to be taken into account, as shown here.”

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