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suspected second coloring agent in the GRS has ever been conclusively identified. If there is a second coloring agent in the GRS, it is unclear whether it is produced at some depth or if it is caused by the UV irradiation of lofted material over the GRS. Since cyclonic systems can also be red, it would appear that something from depth should be responsible or at least a contributor to the reddening. This material from depth might be always red or it may turn red over short exposure to UV photons [137]. The compound NH4SH could be a possibility, since it turns red in only a few hours when exposed to UV photons (Simon-Miller, personal communication).

Images taken by HST on April 8, April 16, and April 24, 2006 indicated that oval BA was now clearly red. However, white clouds seen in the methane-band images indicated that the color was not caused by a longer path length through colored haze, nor was it a clearing out of haze and clouds. This was further evidence of a second coloring agent [138]. There have been other, short-lived, storms that are cyclonic that have taken on red coloration. When they are super red, they seem to be free of any overlying haze, indicating big holes in the upper hazes. Again, this is a good argument that there is something from below that can be quite red (Simon-Miller, personal communication). The presence of a second coloring agent in both oval BA and the GRS indicated that the storm had likely intensified and was isolating material in much the same manner as the GRS. A comparison of rotational velocities measured by the Voyager and Galileo spacecraft, and later by the Cassini spacecraft and the HST shows increased vorticity. This increased vorticity could provide the mechanism for dredging material from some depth, allowing the darkening of oval BA. Thus, this normally white storm appears to have intensified to become more like the GRS [139]. Future observations of oval BA may lead to clues that will finally unlock the mystery into the red color of the GRS and other ovals. Certainly, amateurs with CCD and web cams will play an important role in this research.

There have been entire studies devoted to determining the cause of Jupiter's color, and there are theories that have gained support among scientists. However, most are unproven. While we are fairly sure that the white clouds of the zones are made of ammonia ice [140], the most fundamental questions about Jupiter, such as what colors its clouds, have yet to be answered [141].

In summary, we believe that color on Jupiter does not depend upon chemical composition. Potential color substances, agents that affect the shape of the reflection spectrum, are referred to as chromophores. Astronomers believe that Jupiter's visible cloud structure is dominated by hazes in the upper troposphere and the stratosphere, and by condensate clouds of ammonia, ammonium hydrosulfide, and water at deeper levels. The hazes in the upper troposphere and stratosphere may interact with ultraviolet light, producing hydrocarbon smog that rains down, coloring the cloud tops in the troposphere. The distinct clouds in the troposphere that reside at different depths, may also affect the visual appearance of color. E o ®

Ammonia ice clouds that well up to higher altitudes due to convection will appear <D «jg §

white. The core of the GRS is the reddest of all areas on the planet. A coloring agent, CL

different from the rest of the planet, may be responsible for the redness of the GRS. s ^

And the bluish-gray 5-|jm hot-spots of the NEBs are not colored at all, but result ¡5 g JE

from the absence of ammonia clouds. "5 O

Hopefully the preceding discussion, though somewhat complicated, will help U V O

us understand the difficulties involved in understanding color in Jupiter's atmosphere. And, while the techniques discussed at present might be the realm of the professional, it should be noted that many amateurs today are imaging Jupiter

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