Jovian soot from cometary impacts?

It seems to be widely accepted that the dark spots on Jupiter caused by the impacting fragments of comet Shoemaker-Levy 9 are due to dust particles which have formed immediately after the impacts. However, the actual nature and origin of these grains is still uncertain. We propose that they may consist of amorphous carbon and have calculated the time-dependent formation and growth of such dust particles assuming an exponential pressure decrease in an adiabatic fireball. The resulting properties of the grains, e.g. their sizes, are consistent with observations, The question whether carbon or silicate grains will form depends critically on the chemical composition of the Jovian atmosphere. If a carbon-rich environment exists at the impact sites our model demonstrates that there is enough time to grow amorphous carbon grains in the fireballs rising immediately after the impacts.