The Huygens probe will detach from Cassini on 25 December and enter Titan's atmosphere on 14 January. It will provide us with our first views of what lies beneath Titan's photochemical haze.

Huygens will send back an analysis of the atmosphere's composition and density before it hits the moon's surface. Scientists hope that the probe will land in a liquid sea of hydrocarbons, and that sonar sensors will detect the depth of the strange ocean. An accelerometer will record any bobbing motion in the craft caused by waves on the sea. Measuring how much a beam of light bends as it passes through a sensor will provide information about the fogginess of the lower atmosphere.

The probe is named after Christiaan Huygens (1629-1695), who was the first astronomer to realise that Titan was a satellite of Saturn. He also invented the pendulum clock.