Titan, a moon with phantom lakes and organic seas

Hyperaxion November 15, 2020 1:47 am

Among Saturn’s moons, Titan is perhaps the most extravagant example of exotic chemistry within the Solar System.

At 1.5 times the size of our Moon, and with average temperatures of -180 degrees Celsius, Titan has a hydrological cycle very similar to that of Earth.

As we well know, under normal conditions, water freezes at 0 degrees Celsius. So how could a hydrological cycle be possible at such extreme temperatures?

This is due to the fact that on Titan, there is no liquid water, but liquid ethane and methane.

Such molecules, when exposed to extremely low temperatures or very high atmospheric pressures, condense, thus forming liquid reservoirs of organic molecules.

An artist's impression of Titan's topography.
An artist’s impression of Titan’s topography. (Credit: NASA / JPL-Caltech).

Because Titan’s topography is practically flat, most of these organic lakes do not form deep deposits. For this reason, many of these lakes and seas are quite dynamic.

Throughout the seasons, they disappear and only condense again in the winter. However, it is not that simple.

These phantom lakes were recently discovered thanks to observational data from the Cassini-Huygens space-research mission.

The problem is that the data does not span a very long period of time. To confirm the reappearance of such lakes on Titan’s surface, we would need an orbiter probe like the ones we have today orbiting the Moon and Mars.

However, the existence of these lakes shows not only Titan’s atmospheric complexity but also a possible interaction between atmosphere and geosphere in these hydrological cycles.

Inner layers of Titan. This artist's concept shows a possible model of Titan's internal structure that incorporates data from NASA's Cassini spacecraft.
Inner layers of Titan. This artist’s concept shows a possible model of Titan’s internal structure that incorporates data from NASA’s Cassini spacecraft.

Liquid-solid interaction promotes changes in Titan’s atmosphere

Even with lakes only a few centimeters deep, Cassini’s infrared data revealed seas up to 100 meters deep.

Such structures have the ability to change the climate across the moon and possibly even Titan’s geology.

Visual evidence of the disappearance of lakes on Titan produced by a VIMS infrared spectrometer.
Visual evidence of the disappearance of lakes on Titan produced by a VIMS infrared spectrometer. (Credit: NASA / Johns Hopkins Applied Physics Laboratory / University of Arizona / University of Idaho / JPL-Caltech / ASI / IPGP / CNRS).

This dynamic can promote the differentiation of rocks and minerals and perhaps even facilitate condensation reactions involving possible transition metals, metal alloys, and simple organic molecules.

This process gives rise to polycyclic compounds, potential energy carriers in prebiotic reactions.

The presence of an intricate hydrological cycle with a perennial dynamic on Titan is the best and only known example, with the exception of Earth, of a celestial body with lakes and seas in liquid form.

It is worth remembering that to this day, the Earth is the only celestial body with vast amounts of water that, throughout geological ages, has altered the planet’s atmosphere and geology.

Diameter comparison of Titan, Moon and Earth.
Diameter comparison of Titan, Moon and Earth. (Credit: NASA).

One of the current theories for the origin of life concerns condensation reactions promoted by molecular hydrogen, together with organic molecules such as carbon dioxide (CO2).

The fact that Titan already has compounds such as methane and ethane may be an indication of the presence of other intermediary compounds between these organics.

Even in small concentrations, these potential molecules can play a determining role in the formation of molecules important for life as we know it.

The seeds of life are scattered throughout the Cosmos

We already know that molecules like cyanomethanimine and ethanamine were found in a large dust cloud twenty-five thousand light-years from Earth in 2013.

The first molecule is a precursor to adenine, one of the four nitrogenous bases that make up the structure of DNA.

The second, in turn, has an important role in the formation of alanine, one of the most common amino acids found in proteins.

Therefore, it is quite clear that some important probiotic compounds can be found outside of Earth.

However, the discovery of structures so similar to the lakes and seas that we have on our planet is a big surprise that opens up countless possibilities with regard to extraterrestrial prebiotic chemistry.

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