Titan

Cassini image of Titan with Enceladus in the foreground (NASA/JPL/Space Science Institute)		Cassini image of Saturn's cloud-covered moon Titan (NASA/JPL/Space Science Institute)		Cassini image of Titan in orbit above the planet Saturn (NASA/JPL/Space Science Institute)

The Giant

Titan [TY-tun] is the fifteenth of Saturn's moons and is the largest. It is also the second largest moon in the Solar System. Titan was names after the ancient race of giants in Greek Mythology. They were the children of Uranus and Gaia, who sought to rule the heavens but were overthrown by the family of Zeus. Titan was discovered in 1655 by the Dutch astronomer Christiaan Huygens. Titan was once thought to be the largest planet in the Solar System, but recent discoveries have shown that the Moon's thick atmosphere hides a smaller rocky surface that is slightly smaller than Jupiter's moon, Ganymede. Though it is only the second largest moon in the Solar System, it is still larger than the planets Mercury and Pluto.

False color radar image of Titan showing surface features (NASA/JPL/Space Science Institute)		Cassini closeup of Titan showing layers of clouds and haze (NASA/JPL/Space Science Institute)		False color mosaic showing possible methane lakes (NASA/JPL)

The Moon With an Atmosphere

Even before the Voyager encounters with Saturn, astronomers thought that Titan might have an atmosphere. They also thought that there might be oceans of liquid methane on the Moon's surface. When the Voyager spacecraft finally arrived, all that could be seen of Titan was a dense and impenetrable layer of clouds in a thick atmosphere. Titan was found to have an atmosphere denser than that of Earth and Mars. The atmospheric pressure at the surface is believed to be about 1.6 bars, about 60% greater that on Earth. The atmosphere is composed primarily of Nitrogen with traces of other hydrocarbons such as ethane, hydrogen cyanide, and carbon dioxide. This gives it a rich, orange color. These atmospheric elements are necessary building blocks for life. Astronomers believe that Titan may resemble the Earth at an early stage in its development. They also think that Titan is a prime candidate for the possibility of extraterrestrial life. Titan's surface temperature averages -289°F (-178° C).

Panoramic view of the surface of Titan as seen by the European Space Agency's Huygens probe (ESA/NASA/JPL/University of Arizona )

Features of Titan

Titan is the only known moon with a fully developed, planet-like atmosphere. Unfortunately, this thick atmosphere prevented us from learning much about its surface features during the Voyager missions. What we do know is that it appears to be composed of about half water ice and half rocky material. It is believed to be similar in composition to many of Saturn's other moons, but is much denser because of its large size and higher gravity. Titan's atmosphere is believed to have two cloud layers at about 125 miles (200 km) and 186 miles (300 km) above the surface. It is possible that these clouds produce a rain of liquid methane onto Titan's surface. In fact, it is possible that there may be pools or even oceans of liquid methane on Titan's surface. Recent ground-based radar observations have cast some doubt on this theory, however. Titan has no known magnetic field, and sometimes orbits outside Saturn's magnetosphere. This exposes it directly to the solar wind, which may ionize and remove particles from the atmosphere. In 2004, the Cassini probe arrived at Saturn and dropped a probe called Huygens into Titan's atmosphere. It landed and sent back images of the surface as well as measurements of Titan's atmosphere. Cassini was then able to map Titan's surface using radar, as was done on the Magellan mission to Venus. As amazing as these images were, they only posed more questions than answers. But thanks to Cassini, we have now witnessed some of the most detailed images yet of the ringed planet and her moons.