Not the first but this second planet is the hottest, because its atmosphere causes a severe greenhouse effect
.... Titan's atmosphere is huge and dense, but it is precisely because it is still so... [DOC] [TLE] Greenhouse Gas Emissions: Causes & Sources - Live Science [PAR] Feb 10, 2015 ... A greenhouse gas is any gaseous compound in the atmosphere ... Live Science  
Planet Earth ... the first to quantify the contribution of carbon dioxide to the 
greenhouse ... is the second most abundant gas in our atmosphere, O2 does not 
... global warming partly because of its abundance in the atmosphere.