Titan, Saturn’s icy moon, is an ideal planetary body to study prebiotic chemistry, origins of life, and the potential habitability of an extraterrestrial environment. It has a nitrogen-based atmosphere, complex organic chemistry fueled by radiation from the Sun and Saturn’s magnetosphere, hydrocarbon lakes, organic dunes on the equator, and seasonal evaporation and precipitation of hydrocarbons in a process notably similar to Earth’s hydrological cycle. In new research, planetary scientists recreated the Titan’s conditions in small glass cylinders, revealing fundamental properties of two simple nitrile molecules — acetonitrile and propionitrile — that are believed to exist as minerals on the surface of the icy moon.
Like Earth, Titan has a dense atmosphere and seasonal weather cycles, but the chemical and mineralogical makeup are significantly different. Image credit: Benjamin de Bivort, debivort.org / CC BY-SA 3.0.
Most of what we know now about Titan is thanks to the NASA/ESA Cassini-Huygens mission to Saturn and its moons.
From that mission, planetary researchers know that Titan is a compelling place to study how life came about.
Fueled by the Sun’s energy, Saturn’s magnetic field and cosmic rays, hydrocarbons react on Titan to produce organic molecules of various sizes and complexities.
Acetonitrile and propionitrile are believed to be present in the moon’s characteristic yellow haze as aerosols, and they rain down on the surface, settling as solid chunks of minerals.
The properties of these molecules on Earth are well known, but their characteristics under Titan-like conditions have not been studied until now.
“Simple organic molecules that are liquid on Earth are typically solid icy mineral crystals on Titan because of its extremely low temperatures, down to minus 180 degrees Celsius (minus 290 degrees Fahrenheit),” said Dr. Tomče Runčevski, a researcher at Southern Methodist University.
“In the lab, we recreated conditions on Titan in tiny glass cylinders.”
“We found that acetonitrile and propionitrile occur predominantly in one crystalline form that creates highly polar nanosurfaces, which could serve as templates for the self-assembly of other molecules of prebiotic interest.”
“Our research revealed a lot about the structures of planetary ices that was previously unknown,” he added.
“We found that one crystalline form of propionitrile 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.”
Dr. Runčevski and colleagues presented their results this week at the ACS Fall 2021 meeting of the American Chemical Society.
Tomče Runčevski et al. Simple nitriles as putative cryominerals on Titan, Saturn’s moon. ACS Fall 2021