First-ever asteroid discovered with rings, astronomers agape

Astronomers have discovered an asteroid with rings, the first time such a phenomenon has ever been observed. The discovery was made during a rare astronomical event known as an occultation.

LOS ANGELES, CA (Catholic Online) - The greatest thing a scientist can hear in the laboratory is the dubious phrase, "that's strange." In June 2013, that's how scientists reacted when asteroid Chariklo passed in front of a distant star in an event known as an occultation.

Occultations are rare for asteroids, although one occurred just last week when a major asteroid passed in front of the star Regulus in the constellation, Leo. That occultation was visible only across a narrow band of territory sweeping though New England and it was largely obscured by poor weather.

St. Dominic, patron saint of astronomers.

However, astronomers had no problem viewing the occultation of Chariklo in June 2013.

Scientists expected the asteroid to quickly block the starlight behind it, winking out, then back on some seconds later, but instead they saw the starlight dim and brighten, then go out, then brighten and dim again. This is the telltale sign that the star's light is passing through rings.

Astronomers first detected rings around Uranus and Neptune using the same technique. What is most surprising in this case is that until now, astronomers thought only giant planets could have rings.

Chariklo is 155 miles wide, which the observations confirmed. They also revealed that the asteroid has two rings, an outer ring about 2 miles wide and an inner one 4 miles wide. The rings are separated by a gap of 5.5 miles.

The rings are probably made of water ice. How they got there is a matter of wild speculation, but likely there was a collision long ago which caused ice to be knocked off the asteroid's surface and to fall into orbit around the M&M-shaped rock.

In a stroke of fortune, the asteroid will occult three more stars over the next year because it is passing in front of a field of stars which is easily visible to Hubble and other powerful telescopes. This will allow them to confirm their discovery and take more precise measurements.

This particular asteroid is of interest to astronomers because it is rich in organic material, as are most asteroids which orbit between Uranus and Saturn. These asteroids are collectively classified as "Centaurs."

Astronomers want to determine with greater precision what Centaurs really are because they have properties of asteroids, but are also rich in ice and organics like comets, hence their name.

The discovery is detailed in the current issue of the scientific journal, Nature.

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