  Royal Society Discussion Meeting (2013) `Characterizing exoplanets'. Of the
900+ confirmed exoplanets discovered since 1995 for which we have constraints
on their mass (i.e., not including Kepler candidates), 75% have masses larger
than Saturn (0.3MJ), 53% are more massive than Jupiter, and 67% are within 1 AU
of their host stars. And yet the term `hot Jupiter' fails to account for the
incredible diversity of this class of object, which exists on a continuum of
giant planets from the cool jovians of our own solar system to the
highly-irradiated, tidally-locked hot roasters. We review theoretical
expectations for the temperatures, molecular composition and cloud properties
of Jupiter-class objects under a variety of different conditions. We discuss
the classification schemes for these Jupiter-class planets proposed to date,
including the implications for our own Solar System giant planets and the
pitfalls associated with classification at this early stage of exoplanetary
spectroscopy. We discuss the range of planetary types described by previous
authors, accounting for: (i) thermochemical equilibrium expectations for cloud
condensation and favoured chemical stability fields; (ii) the metallicity and
formation mechanism for these giant planets; (iii) the importance of optical
absorbers for energy partitioning and the generation of a temperature
inversion; (iv) the favoured photochemical pathways and expectations for minor
species (e.g., saturated hydrocarbons and nitriles); (v) the unexpected
presence of molecules due to vertical mixing of species above their quench
levels; and (vi) methods for energy and material redistribution throughout the
atmosphere (e.g., away from the highly irradiated daysides of close-in giants).
Finally, we will discuss the benefits and flaws of retrieval techniques for
establishing a family of atmospheric solutions that reproduce the available
data.
