Scientists have discovered two dense and narrow rings around the asteroid Chariklo. This is the smallest object ever found to have rings -- and only the fifth body in our solar system to sport them.
Chariklo belongs to a class of asteroids called Centaur objects, which orbit primarily between Jupiter and Neptune (unlike the numerous main-belt asteroids between the orbits of Mars and Jupiter). The Centaur object (10199) Chariklo orbits the sun between Saturn and Uranus and has a radius of about 124 kilometers. It’s the largest known Centaur object in the solar system, but still far, far smaller than Jupiter, Saturn, Uranus, and Neptune, which all have rings. Until now, rings in the Milky Way have been found exclusively around those four giant planets.
The two rings have been nicknamed Oiapoque and Chuí, after two rivers near the northern and southern extremes of Brazil. And they were revealed during observations of Chariklo passing in front of a distant star.
A stellar occultation happens when a remote body (like an asteroid) eclipses a star, dimming the starlight briefly. (If you were near New York last week and staring into the southwestern sky, you may have witnessed the asteroid Erigone blocking the star Regulus for several seconds.) Predictions have shown that Chariklo would pass in front of the star UCAC4 248-108672 in June 2013, as seen from South America.
Astronomers using telescopes at seven different locations -- including the 1.54-meter Danish and TRAPPIST telescopes at European Southern Observatory's La Silla Observatory in Chile -- were able to watch the star apparently vanish for a few seconds as its light was blocked by Chariklo. But for a few seconds before, and again for a few seconds after the main occultation, they saw two very short dips in the star’s brightness. In addition to the expected drop in apparent brightness, double rings have also blocked the light.
"We weren’t looking for a ring and didn’t think small bodies like Chariklo had them at all, so the discovery -- and the amazing amount of detail we saw in the system -- came as a complete surprise!" study researcher Felipe Braga-Ribas of the National Observatory in Rio de Janeiro says in a statement.
By comparing observations from different sites, the international team reconstructed the shape and size of the asteroid, along with the shape, width, orientation of the newly discovered double rings. This video shows an artistic view of the ring system, along with the occultation that explains how the detection was made.
The two dense rings have widths of about 7 kilometers and 3 kilometers, and orbital radii of 391 kilometers and 405 kilometers, respectively; they’re separated by a clear gap of 9 kilometers. The researchers think that the rings are partially composed of water ice, and while the rings’ origins remain a mystery, they’re likely the remnants of a disk of debris that resulted from a collision -- and then subsequently confined into narrow rings by small, shepherding satellites.
"So, as well as the rings, it’s likely that Chariklo has at least one small moon still waiting to be discovered," Braga-Ribas adds. After all, rings are often the first step in the materialization of moons.
Want more? You can watch a video of an artist's impression of how the ring system may look close up, and here’s a video of what happened when Chariklo passed in front of a star (don’t blink).
The findings were published in Nature and announced at a press conference today.
Image/video credit: Lucie Maquet
