The Location of the CO2, Fundamental in Clathrate Hydrates and its Application to Infrared Spectra of Icy Solar System Objects

CO2 is present on the surface of many Solar System objects, but not always as a segregated, pure ice. In pure CO2-ice, the fundamental absorption is located near 4.268 micron (2343.3 wavenumbers). However, on several objects, the CO2 fundamental is shifted to higher frequency. This shift may be produced by CO2 gas trapped in another material, or adsorbed onto minerals. We have seen that a mixture of H2O, CH3OH4 and CO2 forms a type II clathrate when heated to 125 K and produces a CO2 fundamental near 4.26 micron. The exact location of the feature is strongly dependent on the initial ratio of the three components. We are currently exploring various starting ratios relevant to the Solar System to determine the minimum amount of CH3OH needed to convert all of the CO2 to the clathrate, i.e. eliminate the splitting of the CO2 fundamental. We are testing the stability of the clathrate to thermal processing and UV photolysis, and documenting the changes seen in the spectra in the wavelength range from 1-5 micron. We acknowledge financial support from the Origins of Solar Systems Program, the Planetary Geology and Geophysics and the NASA Postdoctoral Program

Composition of KBO (50000) Quaoar

Aims. The objective of this work is to investigate the physical properties of objects beyond Neptune-the new frontiers of the Solar System-and in particular to study the surface composition of (50 000) Quaoar, a classical Transneptunian (or Kuiper Belt) object. Because of its distance from the Sun, Quaoar is expected to have preserved, to a degree, its original composition. Our goals are to determine to what degree this is true and to shed light on the chemical evolution of this icy body. Methods. We present new near-infrared (3.6 and 4.5 mu m) photometric data obtained with the Spitzer Space Telescope. These data complement high resolution, low signal-to-noise spectroscopic and photometric data obtained in the visible and near-infrared (0.4-2.3 mu m) at VLT-ESO and provide an excellent set of constraints in the model calculation process. We perform spectral modeling of the entire wavelength range-from 0.3 to 4.5 mu m by means of a code based on the Shkuratov radiative transfer formulation of the slab model. We also attempt to determine the temperature of H(2)O ice making use of the crystalline feature at 1.65 mu m. Results. We present a model confirming previous results regarding the presence of crystalline H(2)O and CH(4) ice, as well as C(2)H(6) and organic materials, on the surface of this distant icy body. We attempt a measurement of the temperature and find that stronger constraints on the composition are needed to obtain a precise determination. Conclusions. Model fits indicate that N(2) may be a significant component, along with a component that is bright at lambda > 3.3 mu m, which we suggest at this time could be amorphous H(2)O ice in tiny grains or thin grain coatings. Irradiated crystalline H(2)O could be the source of small-grained amorphous H(2)O ice. The albedo and composition of Quaoar, in particular the presence of N(2), if confirmed, make this TNO quite similar to Triton and Pluto

Saturn's icy satellites and rings investigated by Cassini - VIMS. III. Radial compositional variability

In the last few years Cassini-VIMS, the Visible and Infared Mapping Spectrometer, returned to us a comprehensive view of the Saturn's icy satellites and rings. After having analyzed the satellites' spectral properties (Filacchione et al. (2007a)) and their distribution across the satellites' hemispheres (Filacchione et al. (2010)), we proceed in this paper to investigate the radial variability of icy satellites (principal and minor) and main rings average spectral properties. This analysis is done by using 2,264 disk-integrated observations of the satellites and a 12x700 pixels-wide rings radial mosaic acquired with a spatial resolution of about 125 km/pixel. The comparative analysis of these data allows us to retrieve the amount of both water ice and red contaminant materials distributed across Saturn's system and the typical surface regolith grain sizes. These measurements highlight very striking differences in the population here analyzed, which vary from the almost uncontaminated and water ice-rich surfaces of Enceladus and Calypso to the metal/organic-rich and red surfaces of Iapetus' leading hemisphere and Phoebe. Rings spectra appear more red than the icy satellites in the visible range but show more intense 1.5-2.0 micron band depths. The correlations among spectral slopes, band depths, visual albedo and phase permit us to cluster the saturnian population in different spectral classes which are detected not only among the principal satellites and rings but among co-orbital minor moons as well. Finally, we have applied Hapke's theory to retrieve the best spectral fits to Saturn's inner regular satellites using the same methodology applied previously for Rhea data discussed in Ciarniello et al. (2011).Comment: 44 pages, 27 figures, 7 tables. Submitted to Icaru

Ethane on Pluto and Triton

International audienceNew spectra of Pluto were obtained with the Gemini Near-Infrared Spectrometer (GNIRS) on the Gemini South 8-m telescope covering the region 1.9-2.5 µm. We have analyzed these data and two spectra of Triton with particular emphasis on a weak absorption feature detected at 2.405 μm. While this wavelength is coincident with a 13CO absorption band that is the isotopic variant of the 12CO band (2.35 μm) seen on both Pluto and Triton, our analysis, supported by new lab spectra of CO, shows that the strength of the 2.405-μm band is much too great to be attributed to any plausible abundance of 13CO. Instead, we identify this band as the 2.4045 μm absorption of pure ethane in solid form (Quirico & Schmitt Icarus 127, 354, 1997). Published models of the spectra of Triton (Quirico et al. Icarus 139, 159, 1999) and Pluto (Douté et al. Icarus 142, 421, 1999) show small variations from the data at 2.28 μm. The addition of absorption from the ethane band at 2.274 μm removes this small discrepancy. We do not see evidence for the 2.461 μm ethane band, although this is a somewhat noisy region of both spectra. Other investigators (Nakamura et al. P.A.S. Japan 52, 551, 2000) noted that Pluto's absorption bands at 2.28 and 2.32 μm are best fit with ethane, but their 2.405 μm region is discrepant with ethane. At longer wavelengths, Sasaki et al. (Ap.J. 618, L57, 2005) noted that models fit their Pluto data best when ethane was added, but they did not clearly identify ethane bands. Estimates of the abundances of ethane on Triton and Pluto suggest that this ice is deposited on relatively short time-scales by precipitation from the atmosphere, where it is produced by photochemistry (Krasnopolsky & Cruikshank JGR 100, 21271, 1995; JGR 104, 21979, 1999)