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A soft solid surface on Titan as revealed by the Huygens Surface Science Package

Abstract

The surface of Saturn's largest satellite—Titan—is largely obscured by an optically thick atmospheric haze, and so its nature has been the subject of considerable speculation and discussion1. The Huygens probe entered Titan's atmosphere on 14 January 2005 and descended to the surface using a parachute system2. Here we report measurements made just above and on the surface of Titan by the Huygens Surface Science Package3,4. Acoustic sounding over the last 90 m above the surface reveals a relatively smooth, but not completely flat, surface surrounding the landing site. Penetrometry and accelerometry measurements during the probe impact event reveal that the surface was neither hard (like solid ice) nor very compressible (like a blanket of fluffy aerosol); rather, the Huygens probe landed on a relatively soft solid surface whose properties are analogous to wet clay, lightly packed snow and wet or dry sand. The probe settled gradually by a few millimetres after landing.

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Figure 1: Acoustic sonar (API-S) surface echoes.
Figure 2: Impact deceleration profiles.
Figure 3: A comparison of penetrometer force profiles for Titan and laboratory analogues.

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Acknowledgements

We acknowledge the work of the SSP Team and the HASI Accelerometer Team both past and present in the design, build, test, calibration and operation of these experiments. This work has been funded by the UK Particle Physics and Astronomy Research Council, The Royal Society, the ESA, NASA, CNES and the Polish State Committee for Scientific Research.

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Correspondence to John C. Zarnecki.

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Zarnecki, J., Leese, M., Hathi, B. et al. A soft solid surface on Titan as revealed by the Huygens Surface Science Package. Nature 438, 792–795 (2005). https://doi.org/10.1038/nature04211

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