Publication
- Names
-
- B. Schmitt
- C. de Bergh
- E. Lellouch
- J.P. Maillard
- A. Barbe
- S. Doute
- Title
- Identification of three absorption bands in the two micron spectrum of Io
- Abstract
- Spectroscopic observations of the trailing face of Io at a resolution of 1.02/cm performed with the FTS (Fourier Transform Spectrometer) on the 3.6-m Canada-France-Hawaii telescope (CFHT) on Mauna Kea confirm the presence of two weak absorption features in the 2-micron region. The first feature occurs at 4704.9 +/- 0.2/cm (2.12545 +/- 0.00010 micron); it is about 6.8% deep and 3/cm wide (FWHM). The second feature is at 5047.1 +/- 1/cm (1.98135 +/- 0.0004 microns) with a broad central core; its depth is about 8% and its width approximately 7/cm. A laboratory investigation of spectra of solid SO2 with relatively thick samples, as well as of mixtures of SO2 with CO2 and H2S, indicates that the two features at 4705/cm and 5047/cm are best explained by the 3nu1 + nu3 and nu1 + 3nu3 modes of solid SO2 around 130 K, respectively. In addition, a careful a posteriori look at our Io spectrum shows the presence of a band at 3933 +/- 1/cm (2.5426 +/- 0.0007 microns) (depth approximately equal to 30% (full width at half maximum (FWHM) approximately equal to 8/cm) due to the 3V3 band of solid SO2, as predicted by our laboratory experiments. The positions and widths of these bands indicate that a temperature gradient may exist between the surface of the frost and several centimeters below and suggest that some SO2 may be mixed at the molecular level with some neutral component. Three different models are proposed to explain the apparent discrepancy between the large variability with longitude on the strong 2457/cm (4.07 micron band and the nearly constant depth of the weak 4705/cm (2.1254 micron) band. The first model involes a large variation in grain sizes (factor 2-3) over Io's hemispheres. The second model assumes a considerable variation in thermal flux with Io's longitude (at 2457/cm, up to 20% of the reflected continuum flux). The third model assumes an uniform layer of coarse grained SO2 frost (a few hundred micrometers in size) with a variable longitudinal coverage of a thin layer of very fine frost grains (less than a few millimeters of micrometer-sized grains). Using the optical constants of solid SO2 measured in the laboratory, we predict the position and depth (greater than or equal to 1%) of about 25 additional absorption features of SO2 frost, in the 2800-5000/cm (2.0-3.6 micron) range, that should be observed in future high quality spectra of Io.
- Keywords
- spectroscopy, transmission, absorption coefficient spectra, band position, band intensity, band vibration mode, near-IR, thermal process, molecular solid, ice, SO2, (33)SO2, (34)SO2, SO(18)O, CO2, H2S, Io
- Content
- instrument-technique, sample, spectral data, band list data, planetary sciences, spectral data use, band list data use
- Document type
- article
- Publication state
- published
- Doi
- 10.1006/icar.1994.1135
- Identifiers
-
- URL: http://dx.doi.org/10.1006/icar.1994.1135]
- bibcode: 1994Icar..111...79S