The Cassini spacecraft has been flying close to Saturn’s largest moon Titan to study it. Cassini took readings of Titan’s gravity to understand the moon’s interior structure better. Varied gravitational readings indicate the moon’s interior is a mixture of rock and ice. The moon was never warmed enough to undergo differentiation. Differentiation allows the heavier materials, like certain rocks, to sink to the center forming a core. Lighter materials such as ice and lighter rocks float to the surface, creating a crust, or outer layer. Titan’s uneven internal mixture is about half ice and half rock. The outer 300 miles of the moon is all ice with no apparent rock. Scientists are still studying how methane is supplied to the surface and if there is an ocean underground.