The design, development and calibration of an impact force transducer or penetrometer, for use on the Huygens spacecraft scheduled to land on the surface of Saturn's moon Titan, is described, The thumb-sized transducer employs a piezoelectric sensing element and is capable of working at cryogenic temperatures. Use of the sensor on a spacecraft imposes several reliability and safely constraints, as well as the desire to minimize mass (the sensor mass is 15 9). The impact force profile, measured at 10 kHz by the sensor, allows estimation of the density and cohesion of the surface material, and its palticle size distribution. Sample profiles for terrestrial materials (sand, gravel and clay) are given.

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Thermal conductivity measurements, presented in this paper (Fig. 3), were made during the descent of the Huygens probe through the atmosphere of Titan below the altitude of 30 km. The measurements are broadly consistent with reference values derived from the composition, pressure and temperature profiles of the atmosphere; except in narrow altitude regions around 19 km and 11 km, where the measured thermal conductivity is lower than the reference by 1% and 2% respectively. Only single data point exists at each of the two altitudes mentioned above; if true however, the result supports the case for existence for molecules heavier than nitrogen in these regions (such as: ethane, other primordial noble gases, carbon dioxide, and other hydrocarbon derivatives). The increasing thermal conductivity observed below 7 km altitude could be due to some liquid deposition during the descent; either due to condensation and/or due to passing through layers of fog/cloud containing liquid nitrogen-methane. Thermal conductivity measurements do not allow conclusions to be drawn about how such liquid may have entered the sensor, but an estimate of the cumulative liquid content encountered in the last 7 km is 0.6% by volume of the Titan's atmosphere sampled during descent.