Titan is Saturn’s largest moon, and the second largest moon in the Solar System, after Jupiter’s Moon Ganymede. In fact, astronomers used to think that Titan was the largest moon, but they learned that it’s surrounded by a thick atmosphere that makes it look a little larger than it really is. Titan measures 5,152 km across, and orbits at an average distance of 1,221,870 km from Saturn. It takes 15.945 days to complete an orbit around Saturn, which is the same as its length of day; Titan is tidally locked to Saturn.
Titan was discovered in 1655 by the Dutch astronomer Christiaan Huygens, and is named after the race of giants in Greek mythology. In fact, all of Saturn’s largest moons are named after specific giants, like Enceladus, Iapetus and Mimas.
Titan is the only moon in the Solar System known to have a full, thick atmosphere with distinct layers. It’s atmosphere was first discovered in the early 20th century, but it wasn’t until its first close visit in the 1980s by NASA’s Voyager spacecraft that astronomers finally got to see this atmosphere up close. The atmospheric pressure down at the surface of Titan is actually thicker than the surface of Earth, measuring 1.5 bars. But unlike Earth, it’s made up almost entirely of nitrogen – 98.4%. The rest is methane and trace amounts of hydrocarbons.
The surface of Titan also contains standing pools of liquid. But not water, like we have on Earth. The surface temperature of Titan is -179° C. So these are pools of liquid methane. Detailed observations by NASA’s Cassini spacecraft have shown that these lakes grow and shrink over the seasons on Titan.
There has only been one spacecraft to ever reach the surface of Titan. When NASA’s Cassini spacecraft arrived at Titan, it released the Huygens probe down to the surface. Huygens survived its descent down through the atmosphere of Titan, and landed gently on the surface, sending back pictures from the ground on Titan.
We’ve also recorded an episode of Astronomy Cast all about Saturn’s Moons. Listen here, Episode 61: Saturn’s Moons.
NASA Solar System Exploration: Titan