ABSTRACT
This chapter is dedicated to presenting the fundamentals of the structure of lowdensityatmospheresthatcorrespondtotwosituations,theupperpartoftheatmospheresofplanetsandsatellitessofardiscussed,andthosebodieswithtenuous atmospheres.Sinceitsphysicalbehaviorisdictatedinpartbytheircommonlowdensitynatureandlowpressure,wetreattheminauniquechapter.However,we separate it in two parts to differentiate the physical and chemical properties of the upperpartofamassiveatmospherefromthetenuousatmospherecasethatisrelated to the presence of the solid surface.
