A team of researchers analyzing new data from NASA/ESA Cassini spacecraft has found that a region on Titan called Ontario Lacus is very similar to the Etosha Pan in Namibia. Both are large, shallow depressions that sometimes fill with liquid.
The new study, published the journal Icarus, shows that landforms and the climatic conditions in the region of Ontario Lacus, the largest lake in the southern hemisphere of Titan, are similar to those of semi-arid regions on Earth, such as the salt pans of southern Africa.
Ontario Lacus is a little smaller than its namesake, Lake Ontario in North America, but otherwise differs from it in some major ways. It is filled with liquid hydrocarbons, not water, and it is only a few meters deep at most, located in an extremely shallow depression in a flat sedimentary basin, surrounded by small mountain ranges.
Ontario Lacus was previously thought to be permanently filled with liquid methane, ethane and propane, but the new study suggests otherwise.
Combining data from Cassini’s imaging, spectroscopic and radar instruments, the team led by Dr. Thomas Cornet of the Université de Nantes found evidence for channels etched into the lake bed within the southern boundary of the depression. These channels remained visible between December 2007 and January 2010, each time the spatial resolution was able to resolve them.
“We conclude that the solid floor of Ontario Lacus is most probably exposed in those areas,” Dr. Cornet said.
In addition, Cassini shows sediments around Ontario Lacus that also indicate the liquid level has been higher in the past.
This is similar to ephemeral lakes on Earth. The team suggests its nearest cousin is the Etosha Pan in Namibia. This salt lake bed fills with a shallow layer water, provided by the rise of the underground aquifer during the rainy season, before evaporating to leave sediments like tide marks showing the previous extent of the water.
The researchers believe that Ontario Lacus is also the result of subsurface hydrocarbon fluids occasionally welling up and flooding the depression, before then partially drying out again.
Beyond Earth, Titan is the only other world known to bear stable liquids on its surface. Where Earth has a water cycle, Titan has a full hydrocarbon cycle, based on hydrogen, carbon and nitrogen, taking place between the atmosphere, the surface and the subsurface. Titan’s lakes are an integral part of this process.
“These results emphasize the importance of comparative planetology in modern planetary sciences: finding familiar geological features on alien worlds like Titan allows us to test the theories explaining their formation,” said Dr. Nicolas Altobelli, ESA’s Cassini–Huygens project scientist.