One of the most fundamental discoveries of the solar system was the
detection of four moons in orbit around Jupiter by Galileo Galilei in
1610. The discovery was significant not only in the context of Jupiter;
it gave credence to and was instrumental in firmly establishing the
heliocentric system of Nicolaus Copernicus. Almost four centuries after
Galileo's discovery, exten- sive observations by the two Voyager
spacecrafts have once again revolu- tionized our thinking about the
major planets, their composition, structure, origin, and evolution. This
book is an attempt at summarizing our present understanding of the
atmospheres and ionospheres in the outer solar system, with particular
emphasis on the relevant physics and chemistry. I was motivat- ed to
prepare this manuscript for the following reasons. First, after under-
going rapid expansion in the recent past, the subject has finally
attained suf- ficient maturity to warrant a monograph of its own.
Second, I have felt that as a result of recent observations, new and
challenging problems have arisen whose resolution requires
unconventional analysis and theoretical interpreta- tion of existing
data, as well as the collection of new kinds of data. I believe the time
is ripe to put these issues in the appropriate scientific perspective,
with the hope of stimulating novel theoretical, observational, and
laboratory studies. I have highlighted the significant scientific
problems throughout the book, especially at the end of each chapter.