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Rain, winds and haze during the descent to Titan

30 November 2005

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Images from the DISR Side-Looking Imager and from the Medium Resolution Imager, acquired after landing, were merged to produce this image. The horizon’s position implies a pitch of the DISR, nose-upward, by 1-2° with no measurable roll. ‘Stones’ in the foreground are 10-15 cm in size, presumably made of water ice, and these lie on a darker, finer-grained substrate.

A region with a relatively low number of rocks lies between clusters of rocks in the foreground and the background and matches the general orientation of channel-like features in the panorama view from 1.2 km (3rd image in article). The scene evokes the possibility of a dry lakebed.

Credits: ESA/NASA/University of Arizona

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Images recorded by the Huygens DISR between 17 and 8 km were assembled to produce this panoramic mosaic. The probe groundtrack is indicated as points; north is up. Narrow dark linear markings, interpreted as channels, cut through the brighter terrain. The complex channel network implies precipitation (likely as methane ‘rain’) and possibly springs. The circle indicates the outline of the low-altitude panorama view from 1.2 km below (3rd image in article).

Credits: ESA/NASA/Univ. of Arizona

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Images recorded by the Huygens DISR between 7 and 0.5 km were assembled to produce this panoramic mosaic. The probe groundtrack is indicated as points; north is up. The ridge near the centre is cut by a dozen darker lanes or channels. The landing site is marked with an ‘X’ near the continuation of one of the channels.

Credits: ESA/NASA/Univ. of Arizona

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This reflection spectrum of the surface was obtained after landing using an on-board lamp (red line). The surface is dark and brownish. The reflectivity shows absorption probably due to water ice. The slope of the reflectivity in the infrared is unlike any existing laboratory measurements. Spectra of two different organic tholins (black lines) are shown for comparison. These laboratory analogues of Titan’s photochemical end-products are consistent with the visible spectrum of the surface but cannot explain its infrared reflection spectrum.

Credits: ESA/NASA/Univ. of Arizona

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These are DISR spectra of the atmosphere of Titan (i.e. changes in the amount of light with colour or wavelength). The light intensity measured by the visible spectrometer looking upward in the direction opposite the Sun increases as altitude decreases. This change in brightness is due to the increase of the number of aerosol particles, scattering the sunlight, above the probe as it descends through the atmosphere.

Visible and infrared spectra recorded in various directions provide information on the number density and properties of the 'haze' particles.

Credits: ESA/NASA/Univ. of Arizona

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This figure shows horizontal wind speed and direction as a function of altitude from DWE and DISR. The green lines are the DISR data and the blue lines are the high-altitude DWE data (showing reasonable consistency between the two).

Titan’s eastward winds slow from about 28 m/s at 50 km to 10 m/s near 30 km, then decrease more rapidly down to 7 km where they drop to zero. Below 7 km, the expected top of the boundary layer, the winds reverse and blow westward.

Credits: ESA/NASA/Univ. of Arizona

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