The planetoid Chariklo (10199) is also a centaur asteroid (see nota opposite), about 250 km in diameter. But this asteroid is particularly surprising, it has 2 rings. During the observation a stellar occultation, a team of astronomers has discovered since the European Southern Observatory, the smallest object with rings, the solar system.
This discovery has been revealed in the magazine Nature March 26, 2014. Surprisingly Chariklo moves in space with two unusual companions, a couple of narrow rings and dense about 7 km and 3 km wide. The two rings are separated by 9 km away and all revolves about 400 km from the center of Chariklo, which is very close at 1.5 times the diameter of the asteroid. The existence of a ring system around a minor planet is unexpected because it was thought that the rings could not be stable unless they revolved around more massive bodies, only the giant planets of our solar system are surrounded by rings. We do not understand how Chariklo can keep its rings over a long period. Astronomers have called rings, Oiapoque (inner ring) and Chui (outer ring) according to two rivers located in Brazil, one in the northern border, the other to the southern border. There is a preferred explanation, the presence of these tiny rings. They are likely to be the remaining debris, impact on Chariklo, a collision with an existing moon. If the rings are formed as a result of impact, the object must have a low speed to avoid being ejected beyond the Hill sphere of Chariklo.
The escape velocity at the Chariklo surface is ≈ 0.1 km/s, the speeds of impact in the asteroid belt are much higher ≈ 5 km/s, the velocities of the solar system external are ≈ 1 km/s, which told scientists that the rings are first formed near the outer solar system, i.e. in the Kuiper belt before drifting Chariklo on its current orbit between Saturn and Uranus. However, scientists do not understand the stability of the rings because collisions between ring particles should fall all the dust on Chariklo a few million years.
This stability requires the presence of an active source of particles or the presence of a very small shepherd moon (see note at bottom right), which confines the rings. This moon would be very difficult to detect by direct imaging from Earth due to small radial distance, of the ring system Chariklo.
NB: Centaurs are asteroids that orbit the Sun between Jupiter and Neptune. Centaurs come from the Kuiper Belt. They are on unstable orbits dynamically that will lead to their ejection from the solar system, to an impact with a planet or the Sun, or will become a short-period comet. The largest member (10199) Chariklo, has a diameter of ≈ 250 km.
|≈ 248x258 km
|Minor planet category
|Oiapoque ring width
|Chuí ring width
|James V. Scotti
|February 15, 1997
|63.17 yr (23,087.2 d)
|Longitude of ascending node
|Argument of Perihelion
Image: The Chariklo orbit farthest from the Sun, is 2.8 billion km, closer to the Sun it is 2 billion km, so it entered the inner orbits of Uranus and Neptune. However, its orbit is more stable (less elliptical) than centaurs asteroids as Nessus (7066), Chiron (2060) and Pholus (5145). Chariklo is 4:3 resonance with Uranus. This is a Danish telescope spotted a strange phenomenon first in June 2013 and three observatories in Chile, Argentina and Brazil have confirmed the same anomaly by observing a star. Chariklo has 2 rings surprisingly stable. This stability requires the presence of an active source of particles or the presence of a very small shepherd moon that confines the rings.NB: a shepherd satellite is a body of a small size, orbiting near the edges of a ring. Gravity generated by the satellite confines the ring and it defines a specific board. Indeed, the particles that moving away are either returned to the ring, or integrated into the moon.