* Astronomy

Titan's surface is like... Professor John Zarnecki explains the surprising answer, and exposes what went on behind the scenes of the Huygens probe. This is an extract from 'Fingers Crossed -- Fifty Years of Space Exploration'.

[youtube=http://youtube.com/watch?v=p0-9t4SfgX8]

Title: Clathrate hydrates as a sink of noble gases in Titan's atmosphere
Authors: C. Thomas, O. Mousis, V. Ballenegger, S. Picaud

We use a statistical thermodynamic approach to determine the composition of clathrate hydrates which may form from a multiple compound gas whose composition is similar to that of Titan's atmosphere. Assuming that noble gases are initially present in this gas phase, we calculate the ratios of xenon, krypton and argon to species trapped in clathrate hydrates. We find that these ratios calculated for xenon and krypton are several orders of magnitude higher than in the coexisting gas at temperature and pressure conditions close to those of Titan's present atmosphere at ground level. Furthermore we show that, by contrast, argon is poorly trapped in these ices. This trapping mechanism implies that the gas-phase is progressively depleted in xenon and krypton when the coexisting clathrate hydrates form whereas the initial abundance of argon remains almost constant. Our results are thus compatible with the deficiency of Titan's atmosphere in xenon and krypton measured by the  Huygens probe during its descent on January 14, 2005. However, in order to interpret the subsolar abundance of primordial Ar also revealed by  Huygens, other processes that occurred either during the formation of Titan or during its evolution must be also invoked.

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Titan update - from 11 Jan 2007

[youtube=http://youtube.com/watch?v=NfK9zslzcSQ]

Cassini's radar instrument obtained its second in a series of four north polar swaths of Titan on April 10, 2007. This image exposes more of the transition between the mid-latitudes and the polar area, and extends coverage of the lakes region previously seen in the Titan T25 flyby on Feb. 22, 2007.


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Credit: NASA/JPL

This swath begins at 20 degrees south, 37 degrees west, continuing approximately north-northeast. Although it appears to be straight in this image, its path on Titan curves gently toward the east until it reaches 80 degrees north at 300 degrees west, then it turns south and ends at 51 degrees north, 213 degrees west. The swath width varies from about 200 kilometres at its centre to about 500 kilometres at the ends, and is more than 6,700 kilometres long.
Beginning at the left end of the image as shown, we see the dark sinuous features previously interpreted to be dunes, interspersed with bright features that appear to be higher. In some cases the dunes seem to bend around the bright features, and in others they may be climbing up onto them; both behaviours are commonly seen in dune fields on Earth. About one-third of the way through the swath, the dunes become rare and then disappear, to be replaced by more linear features. Some of these have rounded and brighter ends, similar to lava flows on Earth (in synthetic aperture radar images, rougher features appear as bright). Just past the midway point, we find relatively flat and featureless terrain with some structures that also resemble flow fronts, followed by a complex area of semi-circular to irregular depressions that may have formed by collapse. These give way to the lakes at the northernmost portion. Here T28 overlaps with the T25 synthetic aperture radar swath, offering stereo coverage that will be used to determine feature heights.
The lakes, which are thought to be filled with a combination of methane and ethane, have complex shorelines that often include channels. Some of these channels have well-developed tributary systems and drain many thousands of square kilometres of the surrounding terrain. As shown in the mosaic, these lakes are likely connected, and may form part of a larger sea. Brighter areas within the lakes may represent the lake bottom - at the radar's 2-centimeter wavelength, it is possible that the liquid is transparent for many tens of meters to the radar, allowing a reflection to be returned from the lake bottom.

Source NASA