Laboratory experiments simulating conditions on the surface of Saturn’s large moon Titan and inside its hydrocarbon lakes suggest nitrogen may dissolve in the cold lakes, then erupt as bubbles and fizz when it separates out of them.
Data returned by NASA’s Cassini spacecraft show variations in the contents of Titan’s lakes and seas, with some having higher levels of ethane than methane.
Nitrogen is capable of dissolving within the liquid methane rains that supply the lakes and seas. But simulations of Titan’s cold surface conditions at NASA’s Jet Propulsion Laboratory (JPL) illustrated that even small changes in the lakes’ and seas’ compositions and temperatures, as well as changes in air pressure, can cause the nitrogen to separate from them and bubble up to the surface.
Known by scientists as exsolution, this process is more likely to occur during seasonal changes that warm up the methane lakes.
“Our experiments showed that when methane-rich liquids mix with ethane-rich ones–for example, from a heavy rain, or when runoff from a methane river mixes into an ethane-rich lake–the nitrogen is less able to stay in solution,” said Michael Malaska of JPL, lead author of a study on the findings published in the journal Icarus.
Bubbles of nitrogen could be responsible for a phenomenon observed by Cassini that has puzzled scientists. The probe’s radar has revealed “islands” that appear and disappear within Titan’s lakes and seas. In at least one case, such an island subsequently reappeared.
These apparent islands could actually be fields of nitrogen bubbles.
“Thanks to this work on nitrogen’s solubility, we’re now confident that bubbles could indeed form in the seas, and in fact may be more abundant than we’d expected,” noted Cassini radar team co-investigator Jason Hofgartner, also at JPL and co-author of the study.
Working with a simulated hydrocarbon lake, the researchers successfully separated nitrogen from an ethane-rich solution. Ethane froze at the “lake’s” bottom, in the process displacing dissolved nitrogen gas, which then separated and rose to the surface.
Nitrogen moves both into the methane and ethane and out of both, much like carbon dioxide moves into and out of Earth’s oceans.
“In effect, it’s as though the lakes of Titan breathe nitrogen,” Malaska said. “As they cool, they can absorb more of the gas, ‘inhaling.’ As they warm, the liquid’s capacity is reduced, so they ‘exhale.'”
Cassini’s 127th and last flyby of Titan will occur on April 22.