Huygens probe. Computer artwork of the Huygens probe (lower centre) descending to the surface of Titan from the Cassini spacecraft (upper left). Titan is the largest moon of the ringed planet Saturn (upper left). Cassini was launched in October 1997 and will reach Saturn in July 2004. It will orbit Saturn for four years, studying the planet, its rings and its moons. The disc-shaped Huygens probe will enter Titan's atmosphere in January 2005. Heat shields will protect and deflect heat from the probe during atmospheric entry, before a parachute opens to slow its descent. The probe is expected to transmit data from Titan's surface for up to 30 minutes.