Constraints On Titan's Surface Composition From 5-µm Cassini/VIMS Observations

Details Constraints On Titan's Surface Composition From 5-µm Cassini/VIMS Observations Constraints On Titan's Surface Composition From 5-µm Cassini/VIMS Observations

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.5706h&link_type=abstract

American Astronomical Society, DPS meeting #39, #57.06; Bulletin of the American Astronomical Society, Vol. 39, p.532

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Observing Titan's surface is complicated by the strong absorbing and scattering properties of the atmosphere. Fortunately, there exist several "windows” between methane absorptions, where the surface is viewable. The 5-µm window is least affected by haze scattering, although the signal is low in this spectral region. We present the results of an extensive search for absorption features in the VIMS hyperspectral data using a statistically unbiased band-fitting algorithm. The approach is optimized for finding narrow absorption lines in the 5-µm window. If a candidate absorption meets any of the following criteria, it is deemed significant: i) The feature is apparent above the noise in the average of all pixels in a dataset. ii) Contiguous subset(s) of an image contain a higher concentration of pixels showing the feature than predicted by the data noise statistics. This excess should be observed consistently in different images containing the region. iii) The feature is spatially correlated with a morphologically and/or spectrally distinct unit, again consistent through time. Using these criteria, one statistically significant absorption is found: near 4.9 µm, it is strongly correlated with the Tui Regio bright anomaly (described by Barnes et al., GRL, 2005). The wavelength location and strength of this absorption are consistent with CO2 ice, likely complexed with other materials such as H2O ice (McCord et al., this meeting). Other localized regions of Titan also show the feature, notably Omacatl Macula (Hayne et al., AGU abstract, 2006). Not finding any other absorptions, for example due to organics predicted to precipitate on Titan's surface (Wilson et al., JGR, 2003), we can place tentative upper limits on the spatial coverage by these hypothetical constituents. The methods described are also being applied to other icy Saturnian satellites.

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