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M.A. Barucci (LESIA, Paris Observatory), D.P. Cruikshank (NASA Ames Research Center), E. Dotto (INAF-OAR), F. Merlin (LESIA, Paris Observatory), F. Poulet (IAS-Orsay), C. Dalle Ore (NASA Ames Research Center), S. Fornasier (Dipart. di Astronomia, Padova), C. de Bergh (LESIA, Paris Observatory)
90377 Sedna is, so far, the largest and most distant trans-neptunian object. It was observed at visible and near-infrared wavelengths using simultaneously two 8.2 m telescopes at the Very Large Telescope of the European Southern Observatory (Cerro Paranal, Chile). The spectrum of Sedna suggests the presence on its surface of different ices (total abundance >50%). Its surface composition is different from that determined for other trans-neptunian objects, and resembles that of Triton, particularly in terms of the presence of \beta nitrogen and methane ices.
In order to test the similarities between the spectra of Sedna and Triton in a quantitative way, we have performed a cross-correlation study of these two spectra, first isolating the 2.0-2.45 \mum region where the absorption features are most prominent. The result of the cross-correlation of the two spectra in this region shows the peak power at (or very near) zero lag, giving a high level of confidence that the spectrum of Sedna has the same main spectral bands (N2 and CH4) as that of Triton in the 2.0-2.45 \mum wavelength region.
The presence of frozen nitrogen on Sedna could imply that there is a thin atmosphere of nitrogen gas surrounding the body during the approximately 200 years of its 10,500-year orbit when it is closest to the Sun. The detection of N2 (if confirmed) suggest that N2 was the dominant form of nitrogen in cold regions of the solar nebula and that Sedna is a representative of the icy planetesimals that helped to form the outer planets.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.