Titan, which is one of the biggest moons of Saturn, has some lakes which are filled with liquid methane. These lakes are surrounded by steep rims that go up to hundreds of feet high. A recently published report by scientists using the radar data from NASA’s Cassini spacecraft suggests that explosions of warming nitrogen created the basins in Titan’s crust.
Apart from the Earth, Titan is the only planetary body in our solar system which is known to have liquid on its surface. But unlike our planet, scientists believe that hydrocarbons such as methane and ethane, which are thought of as gases are available in the liquid state in Titan’s extremely cold climate.
According to a statement by NASA’s Jet Propulsion Laboratory (JPL), most of the models which lay the origin of the lakes on Titan’s surface show liquid methane dissolving the bedrock of ice and solid organic compounds and carving out reservoirs that are filled with this liquid. This might be the origin of a lake having sharp boundaries on Titan. In our planet, water bodies that formed in a similar manner by dissolving the surrounding limestone are called karstic lakes.
The new models of some smaller lakes which are spread across tens of miles differ from that theory. These models propose that small pockets of liquid nitrogen available in Titan’s crust had warmed, thereby turning into an explosive gas which blew out the craters that were later filled with liquified methane. The new theory explains why some of Titan’s smaller lakes such as Winnipeg Lacus that is near the north pole of the giant moon, show up on the radar having steep rims which are sharply higher than sea level. This was difficult to explain by karstic model.
The data was taken by Cassini Saturn Orbiter by NASA during its close flyby of Titan when it prepared for its final jump into the atmosphere of Saturn around two years ago. After seeing the new images, a team of scientists led by Giuseppe Mitri of Italy’s G. d’Annunzio University became convinced that the karstic model did not go well with what they saw.
“We were not finding any explanation that fit with a karstic lake basin. In reality, the morphology was more consistent with an explosion crater, where the rim is formed by the ejected material from the crater interior. It’s totally a different process.” Mitri said in a statement.
The research work which was published on Monday, September 9 in Nature Geosciences, looks at other climate models of Titan and shows that the giant moon may be warm compared to centuries ago.
During the past half-billion to billion years, methane in Titan’s atmosphere has worked as a greenhouse gas, keeping the giant moon relatively warm, but cold by standards of the Earth. Scientists have believed that Titan has gone through multiple different periods of cooling and warming, as methane gets depleted by the solar-driven chemistry and then resupplied.
During the colder periods, nitrogen dominated Titan’s atmosphere, raining down and cycling through the icy crust to collect in pools just below the moon’s surface, Cassini scientist and study co-author Jonathan Lunine of Cornell University said in the statement.
“These lakes with steep edges, ramparts and raised rims would be a signpost of periods in Titan’s history when there was liquid nitrogen on the surface and in the crust,” he noted. Localised warming would have been enough to trigger the liquid nitrogen to vapourise and blow out a crater.
“This is a completely different explanation for the steep rims around those small lakes, which has been a tremendous puzzle,” Cassini Project Scientist Linda Spilker of JPL said.