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| Titel |
IR reflectance spectroscopy of carbon dioxide clathrate hydrates. Implications for Saturn's icy moons. |
| VerfasserIn |
A. Oancea, O. Grasset, E. Le Menn, L. Bezacier, O. Bollengier, S. Le Mouélic, G. Tobie |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063947
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| Zusammenfassung |
| A CO2 spectral band was discovered by VIMS on the Saturn’s satellites Dione, Hyperion,
Iapetus and Phoebe [1]. The band position on the three first satellites corresponds to CO2
trapped in a complex material, but no indication exists whether this latter is water ice or some
mineral or complex organic compound [1]. On Phoebe, the CO2 spectral band is consistent
with solid CO2 or CO2 molecules trapped in the small cages of a clathrate hydrate
structure [2]. It is thought that clathrate hydrates could play a significant role in the
chemistry of the solar nebula [3] and in the physical evolution of astrophysical objects
[4]. But so far, no clathrate hydrate structure has been observed in astrophysical
environments. Moreover, identification of molecules trapped in a clathrate hydrate structure
is extremely difficult because of the strong IR vibration modes of the water ice
matrix.
In this work, experimental IR reflectance spectra for CO2 clathrate hydrates are studied
on grains and films. Clathrates are synthesized in a high pressure autoclave at low
temperatures. IR spectral analysis is made with a low pressure and low temperature cryostat.
These experimental conditions – 80 < T < 110 K, P~10-5 bar - are relevant to icy moons’
surfaces. We have observed that the IR reflectance, in the spectral region (3 - 5 μm)
characterized by H2O and CO2 high absorption coefficients, is strongly dependent on
physical (size, surface) and optical (n and k) properties of the samples. The impact of
these parameters on the CO2 clathrate IR reflectance spectrum will be presented. A
comparison between the absorption bands of CO2 clathrate hydrates obtained in our
lab and CO2 absorption bands as detected by VIMS on the icy satellites of Saturn
will be shown. This experimental work confirms that VIMS data are not consistent
with the presence of structure I CO2 clathrate hydrates on the surface of the icy
moons. Possibility of having metastable structure II still remains unsolved and will be
discussed.
[1] Dalton et al., Space Sci. Rev. 2010, 153 : 113-154.
[2] Cruikshank D.P. et al, Icarus, 2010, 206: 561-572.
[3] Mousis O. et al , Ap. J. 2009, 691: 1780-1786.
[4] Choukroun M. et al, in Solar System Ices, edited by Castillo-Rogez, J. et al., 2011. |
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