Astronomers puzzle over dwarf planet ring system • The Register
Structure appears to be so far out, the Roche limit may need revising
A ring system has been spotted around dwarf planet Quaoar at a distance astronomers didn't believe was possible, defying astronomical theories on how these structures form.
Quaoar lies in the Kuiper belt beyond Neptune. The icy rock is 1,121 kilometers (697 miles) wide, about half the diameter of Pluto. Quaoar is a distant object with interesting properties, including signs it may harbor ice-spewing volcanoes and a ring system.
Debris compressed into rings orbiting planets are found around the gas giants Saturn, Jupiter, Uranus and Neptune, and dwarf planets Chariklo and Haumea. All the ring systems lie relatively close to their host planets within a distance known as the Roche limit.
The Roche limit states that ring systems can only form within a distance where the tidal forces from a larger body are more powerful than a smaller object's own gravitational forces. In short, debris captured inside a planet's Roche limit will be ripped apart and compressed into a ring system. Any material outside this distance, however, will more likely stick together under gravity and form a moon instead.
Quaoar, however, breaks this rule. Its ring system is intact at orbits at a distance over seven times the dwarf planet's radius. Saturn's ring system is located at a distance only three times its radius, for comparison. Now astronomers are puzzled over how such a ring system can survive so far from its parent body. ...
