Huygens probe heat shield. Close-up of the outer surface of the 2.7-metre-wide heat shield (aeroshell) of the Huygens probe. The surface consists of panels of AQ60 ablative material (phenolic resin reinforced by silica fibres). This structure was designed to stabilise and protect the 1.3-metre-wide probe as it entered the atmosphere of Titan, the largest moon of Saturn. Titan's nitrogen atmosphere is 4.5 times as dense as Earth's, and the probe entered on 14 January 2005 at a speed of 20,000 kilometres per hour, generating temperatures of over 12,000 degrees Celsius. After the heat shield had successfully slowed the probe, a parachute was used to bring it safely to the surface.