This image of Jupiter was taken by the Cassini Imaging Science narrow angle camera through the blue filter (centered at 445 nanometers) on October 1, 2000, 15:26 UTC at a distance of 84.1 million km from Jupiter. The smallest features that can be seen are 500 kilometers across.
The contrast between bright and dark features in this region of the spectrum is determined by the different light absorbing properties of the particles composing Jupiter's clouds. Ammonia ice particles are white, reflecting all light that falls on them. But some particles are red, and absorb mostly blue light. The composition of these red particles and the processes which determine their distribution are two of the long-standing mysteries of jovian meteorology and chemistry. Note that the Great Red Spot contains a dark core of absorbing particles. (PIA02666)
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