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[11.04] Geographic Distribution of N₂, CH₄, CO₂, and H₂O Ices on Triton from Near-IR Spectroscopic Monitoring

W.M. Grundy (Lowell), L.A. Young, E.F. Young (SWRI), M.W. Buie (Lowell), J.R. Spencer (SWRI)

We present new 0.8 to 2.4~\mum spectral observations of Neptune's satellite Triton, obtained at IRTF\slash SpeX between 2001 and 2004 as part of an ongoing search for time-variable phenomena associated with Triton's seasonal volatile transport processes, and also perhaps with reported shorter-term "reddening" events. The ability to detect spectral changes on these time scales depends critically on accurate characterization of any cyclic variations resulting from Triton's 5.877 day rotation period. We will report on our observations of periodic variations of Triton's near-IR absorption bands of N₂, CH₄, and H₂O ices, but not of CO₂ ice, in this initial stage of our Triton monitoring program. The observed variations (or lack thereof) give an indication of how these four ice species are distributed in longitude. The most heterogeneously distributed ice is N₂, which shows nearly twice as much absorption on Triton's Neptune-facing hemisphere as on the anti-Neptune hemisphere. Comparison with Voyager-era, visual wavelength imaging of Triton's surface suggest that the observed N₂ ice is concentrated on low-latitude regions of Triton's polar cap, which are predominantly located on the Neptune-facing hemisphere. Non-volatile H₂O ice seems to be slightly concentrated on Triton's leading hemisphere. Despite being highly diluted in N₂ ice, the longitudinal distribution of Triton's CH₄ ice differs from that of Triton's N₂ ice, being slightly concentrated on Triton's trailing hemisphere. Triton's CO₂ ice shows the least longitudinal variation, suggesting that it is either very uniformly distributed or that it is confined to high latitudes.

This work was supported by NASA's Planetary Astronomy and Planetary Geology &\ Geophysics programs, and by NSF's Planetary Astronomy program.

\noindent\hangindent=0.3truein\hangafter=1 Grundy, W.M., and L.A. Young (2004) Near infrared spectral monitoring of Triton with IRTF\slash SpeX I: Establishing a baseline.\ Icarus (in press).

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.