Titan, like Earth, goes through its own seasonal cycle. Titan’s seasonal cycle lasts about seven times longer than on Earth, as Titan’s seasons result from its orbit around Saturn. This seven year seasonal cycle between Titan’s northern and southern hemispheres was noticed by NASA’s Cassini orbiter and is still a subject of ongoing investigation.
The first clues that Titan has seasonal variation came when Cassini spotted a spinning vortex system among the hazy atmosphere above Titan’s north pole. This took place during Titan’s Winter season, when Titan's North pole is pointed away from Saturn. As Cassini continued observing this swirling storm system over time, Titan shifted toward a Springtime orbital position position, which led to a weakening of the vortex system--and the subsequent shift toward Titan’s Summer all but eliminated the vortex system in the northern hemisphere. In other words, Cassini found evidence of a seasonal atmospheric pattern in Titan's Winter hemisphere. This shift in atmospheric circulation with Titan’s orbital period are some of the first indicators that Titan undergoes seasonal variation of its climate.
Titan’s composition and cloud structure also appear to show seasonal variation. The swirling vortex in the northern winter hemisphere also produces a large concentration of exotic gases and other molecules that are usually not found in the rest of Titan’s atmosphere. Titan's Winter hemisphere therefore displays a different atmospheric chemistry, which might even affect the appearance of the night sky. Additionally, clouds are observed to thin at both poles during Springtime conditions, and the height of these clouds even seems to vary with seasons. In general, Titan's Winter hemisphere seems to be cloudier and more turbulent, with conditions becoming milder toward Spring.
Another aspect of Titan that may be affected by its orbit around Saturn is the distribution of lakes on Titan’s surface. Some statistical analyses suggest that Titan’s northern hemisphere have twenty times more coverage of methane and ethane lakes than its southern hemisphere. All else being equal, we might expect Titan to have a relatively even distribution of lakes across its surface, and one suggestion is that this uneven distribution results from Titan’s non-circular orbit around Saturn. Because of this non-circular, or eccentric, orbit of Titan around Saturn, the patterns of evaporation and precipitation of methane will not necessarily be balanced between the north and south hemisphere As a result, Titan tends to accumulate methane in its northern hemisphere, evidenced by its large abundance of lakes.
Further study of Titan will surely reveal even more seasonal features. With Titan, Saturn takes the role of the central orbital object--whereas with Earth, all seasons are in relation to orbit around the sun. Future human colonists on Titan may find some difficulty in adjusting to thinking about seasonal changes relative to Saturn, rather than the Sun. However, perhaps the mere existence of seasons will make Titan more appealing as a home, at least as a reminder of the seasons known on Earth.