This artist's illustration shows the likely interior structure of Saturn's moon Titan, deduced from gravity field data collected by NASA's Cassini spacecraft. The data suggests Titan's interior, cool and sluggish, failed to allow the interior to separate into completely differentiated layers of ice and rock. In addition to the hazy surface of Titan (yellow), the layers in the cutaway show an ice layer starting near the surface (light gray), an internal ocean (blue), another layer of ice (light gray) and the mix of rock and ice in the interior (dark gray). In the background are the Cassini spacecraft and Saturn, not to scale. Image credit: NASA/JPL