Cassini, a spacecraft that orbited Saturn from 2004 to 2017, spotted many lakes on Titan, which is the only other world in the solar system known to have stable bodies of surface liquid. Most of the lakes are found near the moon's north pole, and most are filled with liquid methane and ethane, which are abundant in Titan's atmosphere. However, Cassini also spied several dark patches near Titan's south pole that the researchers thought might be lakes filled with liquid nitrogen.
But that idea has remained controversial, because scientists hadn't pinpointed the source of all of the nitrogen. Scientists have suggested that atmospheric nitrogen might occasionally condense onto the surface, or nitrogen could bubble up from Titan's interior and rise to the surface through underground channels.
To learn more about the lakes, researchers built a simple computer model to look at how nitrogen would behave near Titan's surface. The basic conclusion is that a lake filled with liquid nitrogen could exist near the south pole, which experiences winter temperatures as low as 338 degrees Fahrenheit (170 degrees Celsius). At that temperature, the air near the surface of the lake would get dense enough for the nitrogen to begin condensing, or turning into a liquid, the scientists reported Wednesday (Oct. 9) in the journal Nature Astronomy.
What's more, the calculations suggest that this liquid nitrogen would flow into the lakes, like rain falling from the sky, the scientists said. This inflowing liquid nitrogen would likely produce gas bubbles that rise buoyantly to the surface, they added.
The scientists think that these bubbles might be the source of the bright spots that Cassini sometimes saw above the south-polar lakes. However, the researchers didn't model those bright spots, and they acknowledge that the bright spots might be due to other processes.
For instance, Cassini saw similar bright spots near Titan's north-polar lakes, where the lakes are unlikely to contain liquid nitrogen, the scientists said. In that case, the bright spots might be caused by the evaporation of liquid methane and ethane, which would condense into clouds before dispersing.
