ACS spectra and their associated best fits for two orbits (7067 and 9513) that occurred during the aphelion period of MY35. Diffraction orders 178, 182, and 184 are displayed for each orbit. Order 178 allows the retrieval of CO₂ that is then used to compute CH₄ upper limits in relative abundance. Order 182 hosts the strongest lines of the ν₃ band system and yields the smallest upper limits. The noisier order 184 possesses a distinct double-lobe absorption feature that can be used to discriminate the presence of CH₄ at a level that is around five times higher than in Order 182. Notional CH₄ absorptions (20 and 100 pptv for order 182, and 100 and 500 pptv for order 184) against the observed spectra and centred around the strongest feature of each order are indicated in the small insets.