Minor centaur planet sparks ring mystery
A MINOR planet in our solar system has astronomers thinking in rings.
Or at least thinking about rings and whether they are more common in our solar system than previously thought.
What prompted the focus on rings is a small rocky object called Chiron, just 230km in diameter, known as a centaur. Like its Greek namesake it is a hybrid, displaying characteristics of both asteroids and comets.
Astronomers from the South African Astronomical Observatory (SAAO) and the Massachusetts Institute of Technology (MIT) have now discovered what they think is a system of rings around Chiron.
What intrigued astronomers is that this is the second centaur they have discovered with possible rings around it, suggesting that ring systems are more common in our solar system than previously thought.
The other rings centaur is Chariklo. They say while all our solar system’s gas planets – Jupiter, Saturn, Uranus and Neptune – have rings around them, it was not thought that these smaller bodies would have rings.
Dr Amanda Gulbis of the SAAO, a co-investigator in the study, said in a statement: “The likelihood that Chiron also has a ring system prompts fundamental questions about how planetary rings form and evolve.”
Astronomers are not yet sure if they are rings, or possi- bly a shell of gas, or symmetrical jets of gas and dust shooting out from the centaur’s surface.
“This result is particularly interesting because Chiron is a centaur, a relatively small, cold object that has an unstable orbit in the region of the giant planets. How does a body that is only a few hundred kilometres in diameter, and whose orbit is only stable for a few million years, have a ring system?” said Gulbis.
They have observed what appears to be two separate rings of material around the small planet, about 300km from its centre, one about 3km and the other about 7km wide.
Astronomers have put forward several explanations as to how Chiron may have gained rings. One is that another minor body broke up and the debris was captured by Chiron’s gravitational pull. Another is that the rings formed from left-over material when Chiron itself was formed.
A third is that centaurs started further out in our solar system, but their orbits were altered through gravitational interaction with giant planets, bringing the centaurs closer to the sun. The frozen material would have become less stable closer to the sun, and could have turned into gases that sprayed dust and material off the surface of the body.
Astronomers say if they are to answer these questions, and whether the rings are temporary or permanent, they would need observations by multiple observers over a few hundred kilometres.