Outgassing Behavior and Composition of Comet C/1999 S4 (LINEAR) during Its Disruption

The gas activity of comet C/1999 S4 (LINEAR) was monitored at radio wavelengths during its disruption. A runaway fragmentation of the nucleus may have begun around 18 July 2000 and proceeded until 23 July. The mass in small icy debris (≤30-centimeter radius) was comparable to the mass in the large fragments seen in optical images. The mass budget after breakup suggests a small nucleus (∼100- to 300-meter radius) that had been losing debris for weeks. The HNC,$H_2CO,\>H_2S$, and CS abundances relative to H2Omeasured during breakup are consistent with those obtained in other comets. However, a deficiency in CH3OHand CO is observed.