Titan (moon)
Lakes and seas

Following the Voyager flybys, Titan was confirmed to have an atmosphere capable of supporting liquid hydrocarbons on its surface. However, the first tentative detection only came in 1995, when data from the Hubble Space Telescope and radar observations suggested expansive hydrocarbon lakes, seas, or oceans. The existence of liquid hydrocarbons on Titan was finally confirmed in situ by the Cassini orbiter, with the Cassini mission team announcing "definitive evidence of the presence of lakes filled with liquid methane on Saturn's moon Titan" in January 2007.

The observed lakes and seas of Titan are largely restricted to its polar regions, where colder temperatures allow the presence of permanent liquid hydrocarbons. Near Titan's north pole are Kraken Mare, the largest sea; Ligeia Mare, the second-largest sea; and Punga Mare, each filling broad depressions and cumulatively representing roughly 80% of Titan's sea and lake coverage— 691,000 square kilometres (267,000 sq mi) combined. All three maria's sea levels are similar, suggesting that they may be hydraulically connected. The southern polar region, meanwhile, hosts four dry broad depressions, potentially representing dried-up seabeds. Additional smaller lakes occupy Titan's polar regions, covering a cumulative surface area of 215,000 square kilometres (83,000 sq mi). Lakes in Titan's lower-latitude and equatorial regions have been proposed, though none have been confirmed; seasonal or transient equatorial lakes may pool following large rainstorms. Cassini RADAR data has been used to conduct bathymetry of Titan's seas and lakes. Using detected subsurface reflections, the measured maximum depth of Ligeia Mare is roughly 200 metres (660 ft), and that of Ontario Lacus is roughly 90 metres (300 ft).

Titan's lakes and seas are dominated by methane (CH), with smaller amounts of ethane (C H) and dissolved nitrogen (N). The fraction of these components varies across different bodies: observations of Ligeia Mare are consistent with 71% CH, 12% C H, and 17% N by volume; whilst Ontario Lacus is consistent with 49% CH, 41% C H, and 10% N by volume. As Titan is synchronously locked with Saturn, there exists a permanent tidal bulge of roughly 100 metres (330 ft) at the sub- and anti-Saturnian points. Titan's orbital eccentricity means that tidal acceleration varies by 9%, though the long orbital period means that these tidal cycles are very gradual. A team of researchers led by Ralph D. Lorenz evaluated that the tidal range of Titan's major seas are around 0.2–0.8 metres (0.66–2.62 ft).
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