Free Astronomy Magazine

SMALL BODIES leagues propose several possible scenarios, all relying on the preliminary existence of a disk of debris, including one sufficiently massive to condition with its presence the evolution of the entire structure. That disk could have been originated from material coming from the surface of the asteroid, which entered into orbit following a meteor impact, or from the destruction (for inscru- table reasons) of one or more satellites. A (not very convincing) alternative is that the disk may have derived from a past cometary activity of Chariklo. In the light of current knowledge, the most likely hypothesis seems to be that the ma- terial was ejected from the asteroid as a re- sult of an impact – and then subsequently confined by a relatively massive shepherd- ing body not yet discovered. The small Chariklo’s mass and resultant low escape velocity (only 360 km/h) though re- quire that the impact occurred at a rela- tively low speed, much lower than those typical of today’s interplanetary space occu- pied by Centaurs and by Kuiper belt objects (KBOs) – probable place of origin of the asteroid in question. Prior to that system being perturbed by the initial arrangement of the planetary orbits, the relative veloci- ties among KBOs were lower and the im- pact that favoured the formation of the disk first, and the rings later, could have occurred in that ancient time and in those remote regions of the solar system. This scenario does however raise new questions about the persistence of the rings and about their apparent uniqueness among asteroids. L ight curve of the occultation, recorded in the red band with the TRAPPIST. Outside the occultation, the sum of the flux composed of the contribution by the star and the asteroid is consid- ered = 1. Besides the very sharp drop in flux caused by the passage of Chariklo over the star, we can clearly see the two sec- ondary drops in flux attributable to the rings. The small asymmetries observable in the curve are within the margins of error of the re- cording. [F. Braga- Ribas et al.] Below: video of the occultation with the related light curve. The drop in flux due to the rings sys- tem is easily rec- ognizable. [ESO/ F. Braga-Ribas/ M. Kornmesser] n