Huygens probe. Computer artwork of the Huygens probe (lower centre) descending to Titan, Saturn's (upper right) largest moon, from the Cassini spacecraft (not seen). Cassini was launched in October 1997 and reached Saturn in July 2004. The Huygens probe, which has a diameter of 2 metres, will be released from the spacecraft in December 2004 and start its 22 day journey to the moon. It will reach the atmosphere of Titan in January 2005 and make various atmospheric measurements as it descends. The bottom of the probe is protected by a heat shield, made from thermal tiles similar to those on the space shuttle. After deploying Huygens, Cassini will go into orbit around Saturn.