Volume 512, March-April 2010
Article Number L8
Number of page(s) 6
Section Letters
Published online 07 April 2010

Online Material

\end{figure} Figure 2:

Zoomed image of several CH4 lines showing sensitivity of the spectrum to Triton's methane. Some portions of the spectrum, especially over 2320-2326 nm, are relatively independent of temperature, while high-energy lines at 2353-2359 nm show increased temperature sensitivity. The top two panels show sensitivity to the methane abundance. Blue, red, and green synthetic spectra have 0.03, 0.08, and 0.20 cm-am of methane. Triton's thermal profile is taken from Krasnopolsky (1993) and a Voyager-like vertical distribution is used for methane (Herbert & Sandel 1991, entrance profile). Based on these models, the best fit methane column density is determined to be $0.08 \pm 0.03$ cm-am (i.e. $\pm $40%). The bottom two panels show sensitivity to methane temperature. The previous best-fit model using Voyager thermal profile is shown in pink. Other models assume an isothermal atmosphere with temperature of 30 K (dark blue), 50 K (red) and 80 K (green). These fits indicate a mean methane temperature of 50 +20-15 K.

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\end{figure} Figure 4:

The eight detected CO lines from Triton's atmosphere. X-axis units are nm and Y-axis units are arbitrary. Lines are compared with models including 0, 0.03, 0.30, and 3 cm-am of CO. The slow change in absorption depth with change of column density is caused by heavy saturation of particularly narrow Doppler-shaped lines at $T \sim 50$ K. Based on these models, the best fit CO column density is determined to be 0.30 cm-am with a factor of 3 uncertainty.

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