Saturn has 82 moons. The largest is Titan, which aside from Earth is only other body in space known to maintain liquid pools on its surface. The moon has a dense atmosphere made up predominantly of nitrogen; there's also a bit a methane in the air. Titan is thought to be a good place to investigate how life arose on Earth. Even though the chemistry and mineralogy are different, it has seasonal weather cycles. Researchers have now been able to mimic the conditions on Titan in a tube here on Earth. The work has revealed new information about organic molecules that are thought to be minerals on Titan.
This work is being presented at the annual meeting of the American Chemical Society (ACS), which is both virtual and in-person this year.
“Simple organic molecules that are liquid on Earth are typically solid icy mineral crystals on Titan because of its extremely low temperatures, down to -290 F,” said the principle study investigator Tomče Runčevski, Ph.D. “We found that two of the molecules likely to be abundant on Titan: acetonitrile (ACN) and propionitrile (PCN) occur predominantly in one crystalline form that creates highly polar nano surfaces, which could serve as templates for the self-assembly of other molecules of prebiotic interest.”
The organic molecules on Titan are thought to be the product of reactions between nitrogen and methane that are powered by the magnetic field and cosmic rays emanating from Saturn, as well as energy from the Sun. Organic chemicals of various sizes complexity levels may be produced, including ACN and PCN, which may exist as aerosols that are showered onto the surface, forming solid chunks.
We know a lot about the characteristics of Earth-bund chemicals, but the properties of these molecules as they exist on Titan was a mystery. In this study, researchers modeled Titan's environment using little glass cylinders. Runčevski explained that “typically, we introduce water, which freezes into ice as we lower the temperature to simulate the Titan atmosphere. We top that with ethane, which becomes a liquid, mimicking the hydrocarbon lakes” that were found by the Cassini-Huygens mission that studied Saturn and its moons.
Nitrogen, and then ACN and PCN are added to the glass cylinders, simulating a shower of chemicals. The temperature is raised and lowered slightly to copy the fluctuating temperature on Titan. The researchers used various instruments to evaluate the crystals that formed.
“Our research revealed a lot about the structures of planetary ices that was previously unknown,” Runčevski said. “For example, we found that one crystalline form of PCN does not expand uniformly along its three dimensions. Titan goes through temperature swings, and if the thermal expansion of the crystals is not uniform in all directions, it may cause the moon’s surface to crack.”
Crystals of ACN, PCN and their mixtures are being generated so that they can be compared to a spectral library generated from data collected by Cassini-Huygens.
Source: American Chemical Society