Layers of Titan, cutaway illustration. Model of Titan's internal structure based on data from NASA's Cassini spacecraft (upper left). In this model, Titan's denser core has separated from its outer parts. From outer to inner, the layers are: the organic-rich atmosphere and surface (orange), the de-coupled outer shell (white, water-ice and clathrates), the global subsurface ocean (blue), the high-pressure ice VI shell (white), and the hydrous silicate core (yellow, around 2000 kilometres in radius). Cassini has been orbiting Saturn since 2004. Titan (5150 kilometres across) is the largest moon of Saturn (top right), with another moon (Enceladus) also shown. The Sun is at top left. This model of Titan was developed by Dominic Fortes of University College London, UK. Image published in 2014.