The Breakup of C/1999 S4 (Linear), Days 0–10

The evolution of the morphology of C/1999 S4 (LINEAR) is examined from aseries of images taken from shortly before the disruption of the nucleus until10 days afterwards. This is combined with light curve data to provide a uniquedocumentation of the early evolution of the disruption event. Neither imagesfrom the 1-m Jacobus Kapteyn Telescope nor the 2.5-m Isaac Newton Telescopeat the Roque de los Muchachos Observatory (La Palma, Canary Islands, Spain)show no evidence of bright sub-nuclei, although the presence of a well-definedstable lance-point structure in the head of the comet indicates that a dust and gasproducing source remained active in this region. The centre of brightness of thecoma moved in the anti-solar direction at a few tens of metres per second afterdisruption indicating that it was a mainly dust structure. The contrast in thefragmentation history of comets such as C/1999 S4, C/2001 A2 and 141P/Machholz2 suggests that there is a wide variation in nucleus properties from highly unstableand loosely bound rubble piles to relatively consolidated conglomerates.