-- Smith et al., 2007 https://search.proquest.com/openview/cba4766420ef04f09227ccf861784a90/1?pq-origsite=gscholar&cbl=40569 The upper atmospheres of the four Solar System giant planets
exhibit high temperatures that can not be explained by the
absorption of sunlight.
I have argued that escape is favored over return to surface, since
higher layers are colder and lower density, and so must
exhibit narrower GHG
absorption lines; while lower layers must have broader
absorption lines; so recapture is more likely going down than going up.