36th DPS Meeting, 8-12 November 2004
Session 11 Pluto, Triton, and TNO Surfaces
Oral, Tuesday, November 9, 2004, 10:30am-12:00noon, Clark

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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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