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We obtained Pluto's spectrum using the CSHELL echelle spectrograph at NASA's IRTF on Mauna Kea, on 25-26 May 1992, with a spectral resolution of 13,300. The spectral range (5998-6018 [cm.sup.-1], or 1661.8-1666.9 nm) includes the R(0) and the Q(1)-Q(9) lines of the 2[v.sub.3] band of methane. The resulting spectrum shows the first detection of gaseous methane on Pluto, with a column height of [Mathematical Expression Omitted] ([Mathematical Expression Omitted] x [10.sup.19] molecule (3.22-2.34 X [cm.sup.-2]).

We present spectra of Comet Hale-Bopp (C/1995 O1) covering the range 1.4-2.5 [[micro]meter] that were recorded when the comet was 7 AU from the Sun. These spectra show broad absorption features at 1.5 and 2.05 [[micro]meter]. While we recognize that much of the light from the comet is scattered from the coma, we show that some, but not all, of the absorption features can be matched by an intimate mixture of water ice and a low-albedo material such as carbon on the nucleus. Furthermore, the absence of the 1.65-[[micro]meter] absorption feature of crystalline ice suggests that the cometary ice was probably in an amorphous state at the time of these observations. An unidentified additional component may be required to account for the downward slope at the long-wavelength end of the spectrum.

Spectroscopic studies of the trailing face of Io reveal two weak absorption features in the 2 micrometer region of Io's spectrum. The spectroscopic studies are performed at a resolution of 1.02 per centimeter using Fourier transform spectroscopy. These spectral features consisting of three absorption bands are produced by the 3nu1 + nu3 and nu1+ 3nu3 modes of solid SO2 in the satellite's atmosphere.

Deuterium on Mars: The Abundance of HDO and the Value of D/H THE GEOMORPHOLOGY OF THE MARTIAN surface indicates that running water was present in the distant past, but the [...]

This paper presents the analysis of near-infrared observations of the icy surface of Triton, recorded on 1995 September 7, with the cooled grating spectrometer CGS4 at the United Kingdom Infrared Telescope (Mauna Kea, HI). This analysis was performed in two steps. The first step consisted of identifying the molecules composing Triton's surface by comparing the observations with laboratory transmission spectra (direct spectral analysis); this also gives information on the physical state of the components. Most of the bands in Triton's spectrum were assigned to specific vibration bands of the [CH.sub.4], [N.sub.2], CO, and C[O.sub.2] molecules previously discovered. A detailed comparison of the frequencies of the [CH.sub.4] bands confidently indicated that this molecule exists in a diluted state in solid [Beta]-[N.sub.2]. Three new bands peaking at 5717, 5943, and 6480 [cm.sup.-1] (1.749, 1.683, and 1.543 [[micro]meter], respectively) were also observed. Laboratory experiments have shown that [C.sub.2][H.sub.6] isolated in solid [N.sub.2] fits well the second band, but this would imply the appearance of unobserved bands and thus rules out this assignment. However, [C.sub.2][H.sub.6] may exist in another physical state, and more experiments are necessary. No plausible candidate was found for these three bands when comparing with the spectra of nine molecules ([C.sub.2][H.sub.2], [C.sub.2][H.sub.4], [C.sub.3][H.sub.8], N[H.sub.3], S[O.sub.2], [HC.sub.3]N, [CH.sub.3]OH, NO, N[O.sub.2]). In view of the results of D. P. Cruikshank et al. (1993, Science 261, 742; in preparation), the work presented here leads to two possible representations of the surface of Triton. First, a two-region surface composed of a [N.sub.2]: [CH.sub.4]: CO terrain, [N.sub.2]: [CH.sub.4] :CO consisting of a solid solution in which [N.sub.2] is the dominant molecule, and of a [H.sub.2]O + C[O.sub.2] terrain, composed of a mixture of pure crystalline [H.sub.2]O and C[O.sub.2] grains. The second representation is a three-region surface composed of a [N.sub.2] : [CH.sub.4]: CO terrain and two geographically separated [H.sub.2]O and C[O.sub.2] terrains. The second step of the analysis consisted of using a bidirectionnal reflectance model (S. Doute and B. Schmitt 1998, J. Geophys. Res. Planets 103, 31367). The modeling first confirms the direct spectral analysis in that [CH.sub.4] is diluted in solid [Beta]-[N.sub.2], giving a high degree of confidence to the conclusion that the [N.sub.2]: [CH.sub.4]: CO terrain is in fact a solid solution. It also provides numerical information on this terrain, namely the size of the grains, the geographical abundance, and the [CH.sub.4] and CO concentrations. The large grain size (around 10 cm) would mean that the texture of this terrain is a compact crystalline solid rather than granular, which is in agreement with calculations from J. Eluszkiewicz (1991, J. Geophys. Res. 96, 19,217). In addition, an accurate modeling of the [N.sub.2] band could suggest that the temperature is greater or equal to 35.6 K. Although undistinguishable in the spectra, a maximum of 10% surface area of pure [CH.sub.4] ice can be present at the surface of Triton, thus explaining the high atmospheric [CH.sub.4] abundance observed by Voyager 2. Finally, the modeling showed that none of the two- or three-region representations was able to fit simultaneously the K and H regions of the spectrum of Triton. The origin of this misfit is not yet elucidated, but an instrumental effect is suspected. Some questions about the physical state of the [H.sub.2]O and C[O.sub.2] molecules are thus raised, but unfortunately observational constraints are missing. New near-infrared observations could partly provide these missing constraints, and would be important for detecting new molecules on Triton's surface. Such new data would be especially useful to identify the three bands at 5717, 5943, and 6480 [cm.sup.-1] (1.749, 1.683, and 1.543 [[micro]meter]). Key Words: Triton; infrared spectroscopy; ices; surfaces; satellites.