Known Space -- Sol -- Saturn -- | Titan |
Titan is the fifteenth of Saturn's satellites and the largest. It was long thought that Titan was the largest satellite in the solar system but observations have shown that Titan's atmosphere is so thick that its solid surface is slightly smaller than Ganymede's. Titan is nevertheless larger in diameter than Mercury and larger and more massive than Pluto.
Titan is about half water ice and half rocky material. It is differentiated into several layers with a 3400 km rocky center surrounded by several layers composed of different crystal forms of ice. Its interior is still hot. Though similar in composition to Rhea and the rest of Saturn's moons, it is denser because it is so large that its gravity compresses its interior.
Alone of all the satellites in the solar system, Titan has a significant atmosphere. It is thick and opaque; the surface cannot be seen at all in visible light. At the surface, its pressure is more than 1.5 atmospheres. It is composed primarily of molecular nitrogen (as is Earth's) with no more than 6% argon and a few percent methane. Interestingly, there are also trace amounts of at least a dozen other organic compounds (ie. ethane, hydrogen cyanide, carbon dioxide). The organics are formed as methane, which dominates in Titan's upper atmosphere, is destroyed by sunlight. The result is similar to the smog found over large cities, but much thicker. These hydrocarbon rich elements are the building blocks for amino acids necessary for the formation of life. Scientists believe that Titan's environment may be similar to that of the Earth's before life began putting oxygen into the atmosphere.
Titan has no magnetic field and sometimes orbits outside Saturn's magnetosphere. It is therefore directly exposed to the solar wind. This may ionize and carry away some molecules from the top of the atmosphere.
At the surface, Titan's temperature is about -178 degrees C. At this temperature water ice does not sublimate and the water at the surface cannot participate in the chemistry of the atmosphere. Nevertheless, there is a lot of chemistry going on. Methane is below its saturation pressure near Titan's surface; rivers and lakes of methane don't exist, in spite of the tantalizing analogy to water on Earth. On the other hand, lakes of ethane do exist that contain dissolved methane. Titan's methane, through continuing photochemistry, is converted to ethane, acetylene, ethylene, and (when combined with nitrogen) hydrogen cyanide. The last is an especially important molecule; it is a building block of amino acids.
There are two layers of clouds at about 200 and 300 km above the surface. Other more complex hydrocarbons in small quantities are responsible for the orange hue as seen from space.
The ethane clouds produce a rain of liquid ethane onto the surface producing an "ocean" of ethane/methane mixture (up to 1000 meters deep in places). A single "continent" exists on the hemisphere of Titan that faces forward in its orbit.
Orbital Distance: 1,221,900 km (average) Eccentricity: 0.029 Local Year: 15.945 days (15d 22h 41m 24s) Orbital Velocity: 5.573 km/s Inclination: 0.33° Local Day: 15.945 days (15d 22h 41m 24s) Axial Tilt: n/a Diameter: 5,150 km Composition: Rock and ice Density: 1.89 g/cm3 Mass: 1.35 x 1020 tonnes (0.023 earths) Gravity: 0.14 G Escape Velocity: 2.645 km/s Area: 83.3 million km2 Surface Material: Ices, liquid NH3 & CH4 Atmosphere: Thick N2, CH4 Pressure: 1.5 atm Albedo: 0.21 Temperature: -178°C |