The aftermath of the impacts of periodic comet Shoemaker-Levy 9 on Jupiter was studied With the Wide Field Planetary Camera 2 on the Hubble Space Telescope. The impact debris particles may owe their dark brown color to organic material rich in sulfur and nitrogen. The total volume of aerosol 1 day after the last impact is equal to the volume of a sphere of radius 0.5 kilometer. In the optically thick core regions, the particle mean radius is between 0.15 and 0.3 micrometer, and the aerosol is spread over many scale heights, from approximately 1 millibar to 200 millibars of pressure or more. Particle coagulation can account for the evolution of particle radius and total optical depth during the month following the impacts.