Bulk Characteristics
Titan is 5,150 km across, compared to 4,879 km for the planet Mercury, 3,474 km for Earth's Moon, and 12,742 km for the Earth. Before the arrival of Voyager 1 in 1980, Titan was thought to be slightly larger than Ganymede (diameter 5,262 km) and thus the largest moon in the Solar System; this was an overestimation caused by Titan's dense, opaque atmosphere, which extends many kilometres above its surface and increases its apparent diameter. Titan's diameter and mass (and thus its density) are similar to those of the Jovian moons Ganymede and Callisto. Based on its bulk density of 1.88 g/cm3, Titan's bulk composition is half water ice and half rocky material. Though similar in composition to Dione and Enceladus, it is denser due to gravitational compression.
Titan is likely differentiated into several layers with a 3,400 km rocky center surrounded by several layers composed of different crystal forms of ice. Its interior may still be hot and there may be a liquid layer consisting of a "magma" composed of water and ammonia between the ice Ih crust and deeper ice layers made of high-pressure forms of ice. The presence of ammonia allows water to remain liquid even at temperatures as low as 176 K (−97 °C) (for eutectic mixture with water). Evidence for such an ocean has recently been uncovered by the Cassini probe in the form of natural extremely-low-frequency (ELF) radio waves in Titan's atmosphere. Titan's surface is thought to be a poor reflector of ELF waves, so they may instead be reflecting off the liquid–ice boundary of a subsurface ocean. Surface features were observed by the Cassini spacecraft to systematically shift by up to 30 km between October 2005 and May 2007, which suggests that the crust is decoupled from the interior, and provides additional evidence for an interior liquid layer.
An early 2000 study by the DLR Institute of Planetary Research at Berlin-Adlershof placed Titan in a "large icy satellite" group along with the Galilean moons Callisto and Ganymede.
| Size comparison: Titan in infrared (lower left) with the Moon and Earth (top and right) | Titan's theorized internal structure | Mass comparison: At 96% of their total mass, Titan dominates the Saturnian moons |
Read more about this topic: Titan (moon)
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