Saturn's moon Titan may have fizzy lakes
Saturn's largest moon, Titan, is not only one of the oddest bodies in the Solar System, but may also be the fizziest. Through laboratory experiments and data from the space agency's unmanned Cassini deep-space probe, a team of scientists at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California has recreated the conditions on the surface of Titan and have discovered that its lakes and seas may periodically erupt with bubbles like a cosmic soda can.
Liquids, like water, absorb gases based on pressure and temperature. Water constantly absorbs various gases, like carbon dioxide, oxygen, and nitrogen, but how much depends on various factors. Without going into the math, water under higher pressures and lower temperatures absorbs more carbon dioxide, and less under lower pressures and higher temperatures. That's why a can of warm soda goes flat quickly, and a can of pop in a deep-sea habitat doesn't fizz at all.
According to the JPL team, conditions on Titan are like that of a very complex soda can – only in this case, the liquid is nitrogen and the gas is a mix of cryogenic liquids. Titan has a surface temperature of 93.7 K (−179.5° C, -291° F) and an atmosphere made of 95 percent nitrogen and 4.9 percent methane at a pressure of 146.7 kPa (1.45 atm). The lakes and seas are a mixture of hydrocarbons dominated by methane and ethane that fall as rain.
In some ways, this sounds a bit like a very chilly and exotic version of Earth, but here's where things get complicated. During its numerous flybys, the Cassini spacecraft discovered that these bodies of cryogenic liquid varied in composition, which also altered their properties, including the ability to absorb and retain nitrogen. Effectively, the moon sets up conditions where whether absorbing or releasing nitrogen sits on a knife edge and the lakes of the moon are like cans of a certain Irish stout that blast a shot of nitrogen into the brew when opened.
The researchers compared the nitrogen solubility of Titan's seas against observations and calculations by creating artificial lakes to mimic those of the moon. By taking various mixtures of ethane and methane, then subjecting them to temperatures and pressures found on the surface of Titan, the scientists could observe how mixtures behaved and how well they absorbed nitrogen.
What they found was that the lakes could absorb more nitrogen at higher concentrations of methane combined with lower temperatures and higher pressures. But the interesting thing is that, unlike on Earth, the situation isn't stable, especially in Titan's lakes, which are more sensitive to environmental changes than the larger seas. A slight increase in temperature or a sudden shift in the ratio of methane to ethane due to heavy rain or river runoff caused the nitrogen to bubble out of the artificial lakes.
Another thing that may cause the bubble effect is that ethane is very different from water ice. When it freezes, it becomes denser and sinks to the bottom of the lake. As the ethane/methane ratio changes, the lake again cannot hold onto the nitrogen, which bubbles out. This means that the bubbling occurs not only when the lakes get too warm, but also when they become too cold.
According to NASA, if such fizziness does occur on Titan, it will not only be a future tourist attraction, but will have considerable impact on the dynamics of the Titanian lakes, geology, and even for planning future unmanned missions, like robotic submersibles that might be hampered by a sudden outburst of bubbles. In addition, the possibility of fizzy lakes may explain the disappearance of the so-called "magic islands," which the JPL team now believe may be obscured from view by the sudden bubble eruptions.
The study was published in Icarus.
The video below shows nitrogen fizzing out of freezing ethane.