The matter is settled - Titan has liquid lakes on the surface. / Titán, la luna de Saturno, tiene océanos

Lagos sur li superficie de Titan.

There was quite a bit of heated discussion on the space.com forums two years ago over whether the images Cassini has obtained of Titan that show features that really look just like lakes and should logically be lakes, but taking a look at this thread you can see how much discussion there was in spite of that.

Well, to nobody's surprise except a few people that didn't want to admit the obvious, Titan does have liquid lakes on its surface, so that makes it the second body in the Solar System after the Earth with this feature (Europa has huge oceans, but no lakes on the surface):

Scientists have confirmed that at least one body in our solar system, other than Earth, has a surface liquid lake.

Using an instrument on NASA's Cassini orbiter, they discovered that a lake-like feature in the south polar region of Saturn's moon, Titan, is truly wet. The lake is about 235 kilometers, or 150 miles, long.

That doesn't mean they're made of water though:

When VIMS observed the lake, named Ontario Lacus, it detected ethane, a simple hydrocarbon that Titan experts have long been searching for. The ethane is in liquid solution with methane, nitrogen and other low-molecular weight hydrocarbons.

"This is the first observation that really pins down that Titan has a surface lake filled with liquid," VIMS principal investigator and professor Robert H. Brown of UA's Lunar and Planetary Laboratory said. Brown and his team report their results in the July 31 issue of the journal Nature.

"Detection of liquid ethane in Ontario Lacus confirms a long-held idea that lakes and seas filled with methane and ethane exist on Titan," said Larry Soderblom of the U.S. Geological Survey, Flagstaff, Ariz.

The fact that the VIMS could detect the spectral signatures of ethane on the moon's dimly lit surface while viewing at a highly slanted angle through Titan's thick atmosphere "raises expectations for exciting future lake discoveries by the infrared spectrometer," Soderblom, an interdisciplinary Cassini scientist, said.

The ubiquitous hydrocarbon haze in Titan's atmosphere hinders the view to Titan's surface. But there are transparent atmospheric "windows" at certain infrared light wavelengths through which Cassini's VIMS can see to the ground. VIMS observed Ontario Lacus on Cassini's 38th close flyby of Titan in December 2007.

The lake is roughly 20,000 square kilometers, or 7,800 square miles, just slightly larger than North America's Lake Ontario, Brown said. Infrared spectroscopy doesn't tell the researchers how deep the lake is, other than it must be at least a centimeter or two, or about three-quarters of an inch, deep.

Since it's technically a moon it's easy to forget just how big Titan is and that it would be its own planet if it wasn't orbiting another one. Here it is compared to the Earth:



And here are Mercury, Venus, Earth and Mars for comparison:


You can see that it's even larger than Mercury. Jupiter's moon Ganymede is a bit bigger still, though Titan is far more interesting. It's said that due to the thick atmosphere and low surface gravity that humans could theoretically strap a pair of wings to themselves and simply start flying just by flapping them.