Titan is one of the biggest moons in the solar system, and is the most similar object to Earth. The icy world is second in size to Jupiter’s Ganymede and is larger than the planet Mercury.
Titan is very unique in that it is the only moon to have a dense atmosphere. Like Earth, the atmosphere is made up of mostly nitrogen, except this moon also has methane. Standing rivers, lakes, and seas can be found on Titan; the only other place this is found is on Earth. There is also an earthlike cycle of liquid evaporating to clouds and raining back down to the bodies of water. Lastly, Titan has a very similar tilt as the Earth which results in seasons, but because of Saturn’s long revolution around the sun, seasons last about 7 Earth years.
Astronomers think that Titan formed early in the formation of the solar system. Titans nitrogen isotope ratio is similar to comets in the Oort Cloud, and was formed in the same nebula that the Sun was formed in. Titan is also thought to have 5 primary layers of rock, a shell of water ice, salty liquid water, an outer crust of water ice, and a final layer of organic molecules of sand and water. Source