Chariklo: The passing of a minor planet

Chariklo occultation at Gifberg guest farm  Photo courtesy of Jean-Luc Dauvergne.

On 29 April 2014, a rare event was observed throughout Southern Africa: the passing of a minor planet, Chariklo, in front of a distant star. Chariklo is a ~250-km diameter Centaur, an outer Solar System object whose orbit has been perturbed inward by the giant planets. It is located roughly 17 times as far away from the Sun as the Earth. Chariklo recently made headlines when an article in the journal Nature reported that it has a stable ring system – this is the first small body in the Solar System known to have rings.

Predicted path of Chariklo’s shadow

For the 29 April stellar occultation, national and international teams traveled to a number of sites in South Africa and Namibia. Observations were taken on the SAAO 1.9-m telescope in Sutherland, with UCT PhD student Hannes Breytenbach controlling the telescope and SAAO Astronomer Amanda Gulbis operating the SHOC instrument remotely from Cape Town. Although high humidity and cloud in Sutherland forced the telescope to be closed most of the night, data were successfully obtained during the predicted time of the occultation. The star was bright (~13th magnitude), allowing SHOC images to be taken at an exceptionally fast cadence of 0.04s, which corresponded to a resolution of approximately 0.5km in the Chariklo system. Initial analyses suggest that an amateur telescope and observers in Springbok detected Chariklo’s main ring, while the SAAO observations detected a fainter ring.

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