It is believed by some scientists that the atmosphere of gas giants like Jupiter have retained much of their original atmospheric molecules since their formation. This is believed to be due to their higher gravities preventing such molecules from escaping into space.
When you combine the high gravity of gas giants like Jupiter with their distance from the sun in our solar system, the end result is an extremely hostile and ancient atmosphere (by human standards). By studying the atmospheres of Jupiter and other gas giants, science can better theorize the origins of our solar system.
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This entry also posted in the American Military University Introduction to Astronomy newsgroup.