Observing this particular event, called an occultation, was only possible because JWST can see much fainter stars than any other telescope, says Pablo Santos-Sanz, an astronomer at the Andalusian Institute of Astrophysics in Spain and one of the project’s leaders.
“This was unique,” he tells Astronomy. “It allowed us to characterize these rings as never before.”
How Chariklo got its rings
Like other centaurs, Chariklo is a Kuiper Belt object that was dislodged from its original extreme orbit on the edge of the solar system by the gravity of Neptune. As a result, it now orbits the Sun between Saturn and Uranus.
Eventually, Chariklo will likely be swallowed up by Jupiter, especially if it gets nudged closer to the gas giant. But if it does somehow make it to the inner solar system, then it is likely destined to behave more like a full-fledged comet.
Astronomers discovered Chariklo back in 1997. But it wasn’t until a different star passed behind the centaur in 2013 that they noticed a “double blink” shortly before and after the occultation. This indicated that Chariklo hosts rings of material around it, a bit like a tiny saturnian system.
Measurements of the unexpected dips in brightness suggested Chariklo has two rings that orbit about 155 miles (250 km) above its frozen surface.
Santos-Sanz thinks these rings are made up of tiny pieces of the centaur, mostly water ice, that have accumulated in a region with “3:1 spin-orbit resonance” — meaning Chariklo rotates one time for every three times the material orbits it.
“Particles from the surface of Chariklo can escape the object after impacts from other bodies or meteorites,” he says. “These particles… end up in this special stability region and then form the rings.”
Planning for an occultation
To capture the new observations, Santos-Sanz and his colleagues made weekly predictions of Chariklo’s orbit and updated the position of JSWT accordingly. (The space telescope carries out station-keeping maneuvers to stay at the second Lagrange point [L2], where the Earth shades it from the Sun.)
One of Santos-Sanz colleagues is astronomer Filipe Braga Ribas of the Federal University of Technology Paraná in Brazil, who led the observations that discovered Chariklo’s rings in 2013 using ground-based telescopes in South America.
The latest observations were especially difficult, Braga Ribas tells Astronomy, because JWST was often moving.