Lakes on Earth are a common sight in many locales. They’re central to the recreation and livelihood of millions of people. Few of those people think of the hydrodynamics that happen in a lake system. It is common for lakes to stratify into different layers. On Earth that stratification is the result of the sun heating the upper layer of water, which then becomes less dense and floats on top of the colder, more dense layer beneath it. Now, scientists from the Planetary Science Institute (PSI) have found similar dynamic cycles in a different kind of lake – the ethane and methane lakes on Titan.
Data collected about the surface of the moon make it very clear that Titan has numerous small lakes on its surface. Methane and ethane take the place of water in these lakes, due to the freezing temperatures on the small moon. There is some additional data to suggest that it even rains methane and ethane on Titan’s surface.
Most of the data we have of Titan’s surface, which led to these discoveries, comes from Cassini. Scientists at PSI scoured data on Titan from the spacecraft that plunged into Saturn’s atmosphere in 2017. In that data, they found an interesting quirk of chemistry that could be happening on the moon’s surface.
As stated above, the liquid lakes on Titan are primarily made of methane and ethane. Liquid ethane is more dense than liquid methane, so standard fluid physics would dictate that the methane would float to the top of any free standing lake on the surface. However, at temperatures around those present on Titan’s surface, methane can absorb the nitrogen that is prevalent throughout Titan’s atmosphere. When it does so, the combined methane and nitrogen becomes more dense than the ethane that it shares the lake with. The less dense ethane then floats to the top.
While this is an interesting theory, it has not been backed up by any concrete data yet. NASA is sending a rotorcraft called Dragonfly to Titan, which is expected to land in 2037. Until then, scientists can continue to adjust their models of what is happening in Titan’s lakes. Such models drive home the similarities between Titan’s hydrocarbonological cycle and Earth’s hydrological one. Even so, waterskiing on the lakes on Titan doesn’t seem like a very pleasant experience.
Planetary Science Institute – Titan’s Lakes Can Stratify Like Those On Earth
The Planetary Science Journal – Stratification Dynamics of Titan’s Lakes via Methane Evaporation
UT – Methane-Filled Lakes on Titan are “Surprisingly Deep”
Lead Image – Image of lakes on Titan’s surface. Credit: NASA/JPL-Caltech/ASI/USGS/PSI