H₂O (solid line), CO (long dashed line), and CO₂ (short dashed line) mole fractions as a function of altitude for the three models listed in Table 1. Observations (in blue) from Moreno et al. (2012) (solid lines for mean and 1-σ uncertainty), Cottini et al. (2012) (open triangles), and upper limits from INMS data (Cui et al. 2009) for H₂O, from de Kok et al. (2007) for CO and CO₂ (open diamonds), from Vinatier et al. (2010) for CO₂ (filled diamonds), and from Teanby et al. (2010) for CO (filled triangle) are shown for comparison. Red: Model A1. Green: Model A2. Cyan: Model B. Blue: observations.