First Asteroid Found Sporting a Ring System
Artist's impression of asteroid Chariklo surrounded by two dense and narrow rings. This is the smallest object in the solar system found to have rings and only the fifth body in the Solar System — after the much larger planets Jupiter, Saturn, Uranus and Neptune — to have this feature.
On Wednesday (March 26), astronomers announced the historic discovery of a ring system around asteroid Chariklo, the largest Centaur asteroid that orbits between Saturn and Uranus in the outer solar system. In this artist's impression, the surface features of the asteroid can be seen with one of the dusty rings blocking the view.
Until now, ring systems have only been seen around Jupiter, Saturn, Uranus and Neptune -- this is the first small celestial body found possessing such a ring system and is indicative of an asteroid collision.
As seen from the asteroid's surface, the ring system would appear pretty dramatic when relecting the weak solar light. The 20 kilometer-wide ring system is 1000 times closer than the moon is to the Earth.
The ring system was discovered as the asteroid drifted in front of a distant star, blocking its light from view. This event is known as an occultation and astronomers got more than they bargained for during this particular celestial dance. As predicted, the asteroid blocked light from the star for a few seconds, but just before and just after the event, there was a slight and unexpected dip in starlight brightness. These extra dips have been interpreted as the presence of a dusty ring system around asteroid Chariklo -- an unprecedented find.
When you think of a celestial ring system, the beautiful ringed planet Saturn will likely jump to mind. But for the first time astronomers have discovered that ring systems aren’t exclusive to planetary bodies — asteroids can have them too.
Announced on Wednesday, astronomers using several observatories in South America, including the ESO’s La Silla Observatory in Chile, have discovered that distant asteroid Chariklo possesses two distinct rings. Chariklo, which is approximately 250 kilometers (155 miles) wide, is the largest space rock in a class of asteroids known as Centaurs that orbit between Saturn and Uranus in the outer solar system.
“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!” said lead researcher Felipe Braga-Ribas, of the Observatório Nacional and MCTI, in Rio de Janeiro, Brazil.
Due to the asteroid’s remote location, direct observations of Chariklo’s rings are not possible. Instead, astronomers planned to watch the asteroid drift in front of a distant star — an event known as an occultation, when starlight is blocked for a few seconds. As the asteroid drifted in front of the star UCAC4 248-108672 on June 3, 2013, the astronomers noticed something strange happen to the starlight a few seconds before and a few seconds after occultation: there was a double-dip in starlight brightness.
Astronomers have interpreted this double-dip signal as the presence of a double ring system — the first ever ring system discovered around an asteroid.
“For me, it was quite amazing to realize that we were able not only to detect a ring system, but also pinpoint that it consists of two clearly distinct rings,” said team member Uffe Gråe Jørgensen of the Niels Bohr Institute, University of Copenhagen, Denmark. “I try to imagine how it would be to stand on the surface of this icy object — small enough that a fast sports car could reach escape velocity and drive off into space — and stare up at a 20-kilometre wide ring system 1000 times closer than the moon.”
Artist’s impression of how the rings might look from the surface of asteroid Chariklo.ESO
The astronomers have been able to read incredible details from this observation, including information about the ring system’s shape, orientation and width. There are two sharply confined rings 7 kilometers (4.3 miles) and 3 kilometers (1.9 miles) wide separated by a 9 kilometer (5.6 miles) gap. The rings are being nicknamed Oiapoque and Chuí, two rivers in Brazil.
The ring gap and the ring system’s defined shape is suggestive of the presence of a small satellite in orbit around the asteroid.
“So, as well as the rings, it’s likely that Chariklo has at least one small moon still waiting to be discovered,” said Braga-Ribas.
All this information points to the ring system and hypothetical moon as being debris from an asteroid impact. It seems possible that the moon may be formed out of the ring debris, hinting at the moon formation process that may have spawned Earth’s moon and other moons found throughout the solar system.
This discovery has been published in the March 26 online edition of the journal Nature.