An experimental investigation of atmospheric electricity and lightning activity to be performed during the descent of the Huygens Probe onto Titan

No terrestrial-like electrical activity was observed during the Voyager 1 flyby of Titan on 12 November 1980, in spite of a predicted global lightning energy dissipation rate of 4 × 10⁻⁶ Wm⁻². This lack of evidence does not, however, rule out the existence of electrical discharges with magnitudes, rates of occurrence and spectral characteristics drastically different from those known on Earth, owing to large dissimilarities between the temperatures, chemical compositions and, especially, electrical conductivities of the two atmospheres. Towards the end of the year 2004, the ESA probe Huygens will be jettisoned from the NASA Saturn orbiter, Cassini. This probe will descend onto Titan and perform in situ measurements during a period of 3 h, from an altitude of 170 km down to the satellite surface where the atmospheric pressure reaches 1.6 × 10⁵ Pa. The Huygens scientific payload will include a set of instruments entirely dedicated to the detection of lightning and to the characterization of the electrical properties of the atmosphere and surface. An electric antenna will search for natural emissions in the frequency range 0–10 kHz, at altitudes lower than those of ionized layers opaque to electromagnetic waves, and measure the magnitude of static electric fields due to charge separation. The conductivity of the atmosphere and the existence of free electrons will be checked during the whole descent with a combination of quadrupolar and relaxation probes; a microphone will also record acoustic phenomena associated with electrical discharges and atmospheric processes. The impedance of the surface will be evaluated from the measurements collected with a radar during the descent and a quadrupolar array after touch down.