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Figure 1: a) Spectra of Sedna obtained on two different nights in the V (first night only), J, H, and K regions, with broadband photometric points at B, V, R, I, J, H, and K used to scale the individual segments of the spectra. The spectrum is normalized to 1 at 0.55 m. The second night spectra have been shifted by 2 units for clarity. Assuming a rotational period of 10.27 h, the two K-band observations differ by about 130 in longitude. The strong absorption around 2.3 m appears to be present only on one spectrum, while the band at 2.15 m is present in both spectra. b) Co-added spectrum of Sedna with the best fit model (continuum line).

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In the text

	Figure 2: H and K region spectra of Sedna (continuous line) and Triton (Cruikshank et al. 2000) (dotted line) shown at the same scale and normalized to 1 at 1.65 m. The result of the cross-correlation of the two spectra is limited to the 2.0-2.45 m region.
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In the text

Figure 3: Cross-correlation diagram for the wavelength region 2.0-2.45 m. In each case the lag interval in wavelength was 0.00038 m. a) Sedna spectrum versus a model calculated to provide an approximate match to the strengths of the N2 and CH4 bands. This model is not the same as shown in Fig. 1b, and was calculated with the code of Shkuratov et al. (1999) using 99.7% beta-phase N2 crystalline grains of 700 m size, plus 0.3% CH4 dissolved in N2 in 70 m grains. b) Sedna versus the Triton spectrum (described in the text). c) Triton versus the Sedna model described here. In all three cases, the maximum power peak at or very near zero lag shows that the spectral features in the spectrum of Sedna align favorably with the N2 and CH4 absorption bands in the spectrum of Triton. The broad pedestal in the power distribution between lag intervals of 60 arises from the noise in the Sedna spectrum.

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In the text