File:Alkali metal clouds gas giant.jpg

English: Above 900 K (630°C/1160 °F), carbon monoxide becomes the dominant carbon-carrying molecule in a gas giant's atmosphere (rather than methane). Furthermore, the abundance of alkali metals, such as sodium substantially increases, and spectral lines of sodium and potassium are predicted to be prominent in a gas giant's spectrum. These planets form cloud decks of silicates and iron deep in their atmospheres, but this is not predicted to affect their spectrum. The Bond albedo of a class IV planet around a Sun-like star is predicted to be very low, at 0.03 because of the strong absorption by alkali metals. Gas giants of classes IV and V are referred to as hot Jupiters.55 Cancri b was listed as a class IV planet.HD 209458 b at 1300 K (1000°C) would be another such planet, with a geometric albedo of, within error limits, zero; and in 2001, NASA witnessed atmospheric sodium in its transit, though less than predicted. This planet hosts an upper cloud deck absorbing so much heat that below it is a relatively cool stratosphere. The composition of this dark cloud, in the models, is assumed to be titanium/vanadium oxide (sometimes abbreviated "TiVO"), by analogy with red dwarfs, but its true composition is yet unknown; it could well be as per Sudarsky.HD 189733 b, with measured temperatures 920–1200 K (650–930 °C), also qualifies as class IV. However, in late 2007 it was measured as deep blue, with an albedo over 0.14 (possibly due to the brighter glow of its "hot spot"). No stratosphere has been conclusively proven for it as yet.TrES-2b was measured with the lowest albedo, and therefore listed as class IV gas giant or alkali metal clouds gas giant.