A body in the outer solar system has a ring, and it’s a bit vexing. It’s so far from its host world that it shouldn’t exist. Instead, theories of ring behavior say its material should have stuck together to form a moon.

The host is Quaoar — a dwarf planet. It’s about 700 miles across — a third the size of our own moon. And it’s more than 40 times farther from the Sun than Earth is — in the deep freeze of the Kuiper Belt.

Over several years, astronomers used telescopes on the ground and in space to watch as Quaoar passed in front of four different stars. The way a star’s light fades reveals details about Quaoar, such as whether it has an atmosphere.

Instruments recorded flickers in the starlight shortly before and after each star passed behind the dwarf planet. That indicated the presence of something that’s not completely solid — a ring. It ranges from a few miles to a couple of hundred miles across.

The ring is about 2500 miles from Quaoar. Inside about half that distance, Quaoar’s gravity would keep the ring material from sticking together. At the ring’s current distance, though, a moon should form pretty easily.

The ring might be kept stirred up by Quaoar’s one known moon. Or in the extreme cold, the icy particles that make up the ring might be so hard that they bounce off each other. Whatever the reason, Quaoar has an inconvenient ring — one that hasn’t behaved the way it was expected to.
 

Script by Damond Benningfield