Water ice on Triton

We discuss the spectroscopic detection of H2O ice on Triton, evidenced by t he broad absorption bands in the near infrared at 1.55 and 2.04 mu m. The d etection of water ice on Triton reconfirms earlier preliminary studies (D. P. Cruikshank et al. 1984, Icarus 58, 293-305). Although crystalline H2O ic e has a distinctive spectral band at 1.65 mu m, and our new models slightly favor the presence of this phase, we cannot unambiguously determine whethe r Triton's water ice is crystalline or amorphous. Both phases might be pres ent, and special conditions in the surface microstructure may affect the sp ectroscopic signature of water ice in such a way that crystalline ice is pr esent and its 1.65 mu m spectral band is masked. Our spectra (1.87-2.5 mu m ) taken at an interval of nearly 3.5 years do not show any significant chan ges that might relate to reports of changes in Triton's spectral reflectanc e (B. Buratti et al. 1999, Nature 397, 219), or in Triton's surface pressur e (J. L. Elliot et al. 1998, Nature 393, 765-767). (C) 2000 Academic Press.