what is it composed of?
It is mostly made of molecular hydrogen and helium in roughly solar proportions.
Atmosphere of Jupiter
 It is mostly made of molecular hydrogen and helium in roughly solar proportions; other chemical compounds are present only in small amounts and include methane, ammonia, hydrogen sulfide, and water.
what do the alternating bands of jupiter suggest the presence of The zones' lighter color is believed to result from ammonia ice; what gives the belts their darker colors is uncertain.
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Atmosphere of Jupiter [SEP] Introduction
The atmosphere of Jupiter is the largest planetary atmosphere in the Solar System. It is mostly made of molecular hydrogen and helium in roughly solar proportions; other chemical compounds are present only in small amounts and include methane, ammonia, hydrogen sulfide, and water. Although water is thought to reside deep in the atmosphere, its directly measured concentration is very low. The nitrogen, sulfur, and noble gas abundances in Jupiter's atmosphere exceed solar values by a factor of about three. The atmosphere of Jupiter lacks a clear lower boundary and gradually transitions into the liquid interior of the planet. From lowest to highest, the atmospheric layers are the troposphere, stratosphere, thermosphere and exosphere.