Titan is the biggest of 53 confirmed moons orbiting Saturn (another 9 moons are being confirmed). Titan is a frigid world enveloped by a thick, hazy atmosphere that obscures its surface. Titan has been studied in great detail only in the past few years, with the arrival of the Cassini-Huygens mission at Saturn in 2004.
Titan is the second largest moon in our solar system, with an equatorial radius of 2,575 km (1,600 miles). It is bigger than Earth's moon, and even larger than the planet Mercury.
Only Jupiter's moon Ganymede is larger than Titan, with a diameter barely 112 km (62 miles) greater.
The temperature at Titan's surface is about -178 degrees Celsius (-289 degrees Fahrenheit). At this frigid temperature, water ice is as hard as rock - in fact, most of the rock on Titan's surface is water ice.
Titan orbits Saturn at a distance of about 1.2 million km (745,000 miles), taking almost 16 days to complete a full orbit.
Titan is of great interest to scientists because it is the only other place in the solar system known to have an earthlike cycle of liquids flowing across its surface. That Titan has seas of liquid methane was suspected before the first spacecraft flyby, but its opaque atmosphere prevented close inspection even then. In 1980, NASA's Voyager 1 spacecraft tried to take close up images of the natural features of Titan's landscape, but was unable to penetrate the thick clouds. Instead, the images showed only slight color and brightness variations in the atmosphere. Titan's atmospheric pressure is about 60 percent greater than Earth's -- roughly the same pressure found at the bottom of a swimming pool.
In 1994, NASA's Hubble Space Telescope recorded pictures of Titan, which suggested that a huge bright continent exists on the hemisphere that faces forward in orbit. These Hubble results didn't prove that liquid seas existed, however; only that Titan has large bright and dark regions on its surface.
NASA's Cassini spacecraft (currently orbiting Saturn) has finally revealed the mysterious moon's true nature. Cassini was specially designed to peer through Titan's haze with radar and in certain colors of light, called spectral windows, that allow a glimpse of what lies below. During dozens of flybys, the Cassini orbiter has mapped a large fraction of Titan's surface and made detailed studies of its atmosphere. Cassini also carried the European-built Huygens probe, which parachuted through Titan's atmosphere in 2005 to make the first landing on a body in the outer solar system.
From Cassini-Huygens, we now know that Titan has lakes and seas of liquid methane (natural gas) and ethane near its poles. These bodies of standing liquids appear to grow and shrink in a seasonal cycle as storms bring rain to one hemisphere, then the other. The mission has revealed drainage channels on the surface that were carved by flowing liquid.
Cassini's radar instrument revealed that large swaths of the surface near the equator are blanketed by dune fields, similar to the Namibian desert on Earth. The mission has also found that Titan has an internal ocean of liquid water.
Because of the extremely cold temperatures at Titan's distance from the sun, chemical processes take longer to unfold, leaving the chemistry of the moon's atmosphere in a state of deep freeze. This carbon-rich chemistry is of great interest to scientists because it could be similar to the atmosphere of early Earth, before life emerged on our planet.
Titan was discovered on 25 March 1655 by the Dutch astronomer Christiaan Huygens.
How Titan Got its Name:
The name Titan comes from a generic term for the children of Ouranos (Uranus) and Gaia in ancient Greek mythology. In the stories, the Titans were the ancestors of the human race. The Titans were known to have devoured the limbs of Dionysus, the son of Zeus. Enraged, Zeus struck the Titans with lightning. (Zeus had intended this child to have dominion over the world.) The lightning burned the Titans to ashes, and from the ashes, mankind was formed.